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What is head of a bone?

What is head of a bone?


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For most of the long bones head is the proximal end, but for metacarpals and Ulna, head is the distal end. Why are their distal ends called as heads?

What's the criteria for calling an end as head end?


Here is a head and a neck:

Anatomy is fairly straightforward. regarding individual long bones, "heads" are curved ends of bones distal to a narrowing called a neck of a bone. Take the radius:

See how the radial head (curved) is just distal to a narrowing (neck)?

The ulnar head, though, is at the opposite end, because the proximal end isn't rounded, but the distal end is.

Metacarpal heads are distal (see blue area):

The humeral head is probably most obvious:

So, the head of a long bone is not determined by the position (it can be proximal or distal) but by the contiguous shapes.


Bones Edit

The head rests on the top part of the vertebral column, with the skull joining at C1 (the first cervical vertebra known as the atlas). The skeletal section of the head and neck forms the top part of the axial skeleton and is made up of the skull, hyoid bone, auditory ossicles, and cervical spine.

The skull can be further subdivided into:

  1. the cranium (8 bones: frontal, 2-parietal, occipital, 2-temporal, sphenoid, ethmoid), and
  2. the facial bones (14 bones: 2-zygomatic, 2-maxillary, 2-palatine, 2-nasal, 2-lacrimal, vomer, 2-inferior conchae, mandible).

The occipital bone joins with the atlas near the foramen magnum, a large hole (foramen) at the base of the skull. The atlas joins with the occipital condyle above and the axis below. The spinal cord passes through the foramen magnum.

Muscles Edit

Group Name Nerve Function
facial expression Epicranius: Frontalis and Occipitalis facial nerve eyebrows and scalp
facial expression Orbicularis oris facial nerve closes lips
facial expression Zygomaticus major facial nerve smiling
facial expression Zygomaticus minor facial nerve smiling
facial expression Levator labii superioris facial nerve upper lip
facial expression Levator labii superioris alaeque nasi facial nerve upper lip
facial expression Depressor labii inferioris facial nerve lower lip
facial expression Depressor anguli oris facial nerve frowning
facial expression Platysma facial nerve frowning (during fear or shock)
facial expression Buccinator facial nerve cheeks
facial expression Mentalis facial nerve chin
facial expression Platysma facial nerve frowning
facial expression Risorius facial nerve mouth angle
facial expression Orbicularis oculi facial nerve closes eye
facial expression Nasalis facial nerve flare nostrils
facial expression Corrugator supercilli facial nerve eyebrow
facial expression Levator palpebrae superioris oculomotor nerve upper eyelid
chewing – lower mandible Masseter Trigeminal nerve closing and protruding mandible,
chewing – lower mandible Temporalis Trigeminal nerve elevates and controls side to side movement of mandible
chewing – lower mandible Medial pterygoid Trigeminal nerve elevates mandible,
chewing – lower mandible Lateral pterygoid Trigeminal nerve protracts mandible, opens mouth.
tongue – extrinsic Genioglossus hypoglossal nerve protraction,
tongue – extrinsic Styloglossus hypoglossal nerve elevation and retraction,
tongue – extrinsic Hyoglossus hypoglossal nerve depresses tongue
tongue – extrinsic Palatoglossus Pharyngeal plexus, pharyngeal branch of vagus nerve elevates tongue while swallowing
oral cavity floor Digastric Trigeminal nerve and Facial nerve hyoid and mandible movement
oral cavity floor Stylohyoid Facial nerve elevates hyoid
oral cavity floor Mylohyoid Trigeminal nerve hyoid and mandible movement
oral cavity floor Geniohyoid Cervical nerve C-1 hyoid, tongue, and mandible movement
move head Sternocleidomastoid Accessory nerve nodding and turning
move head Semispinalis dorsal rami of cervical nerves extends head, supports turning
move head Splenius capitis dorsal rami of middle and lower cervical nerves extend head, supports turning
move head Longissimus capitis dorsal rami of middle and lower cervical nerves extends head, supports turning
move head Rectus capitis posterior major Suboccipital nerve C-1 extends head
move head Rectus capitis posterior minor Suboccipital nerve C-1 extends head

Skin Edit

The head and neck is covered in skin and its appendages, termed the integumentary system. These include hair, sweat glands, sebaceous glands, and sensory nerves. The skin is made up of three microscopic layers: epidermis, dermis, and hypodermis. The epidermis is composed of stratified squamous epithelium and is divided into the following five sublayers or strata, listed in order from outer to inner:

    , , , , also called stratum basale. The deepest layer is the miotic layer, stratum basale producing daughter cells by mitosis.

Mouth Edit

The mouth, also called the oral cavity, is the entranceway into the digestive system containing both primary and accessory organs of digestion.

Teeth Edit

Two rows of teeth are supported by facial bones of the skull, the maxilla above and the mandible below. Adults have 32 permanent teeth, and children have 20 deciduous teeth. There are various tooth shapes for different jobs. For example, when chewing, the upper teeth work together with the lower teeth of the same shape to bite, chew, and tear food. The names of these teeth are:

  • (1) Incisors, there are eight incisors located in the front of the mouth (four on the top and four on the bottom). They have sharp, chisel-shaped crowns that cut food.
  • (2) Cuspids (or canine tooth), the four cuspids are next to each incisor. Cuspids have a pointed edge to tear food.
  • (3) Premolars (or bicuspids), the four pairs of molars are located next to the cuspids. They crush and tear food.
  • (4) Molars, there are twelve molars, in sets of three, at the back of the mouth. They have wide surfaces that help to grind food.

The white visible part of a tooth is called the crown. The rounded upper projections of the back teeth are cusps. The hard white exterior covering of the tooth is the enamel. As the tooth tapers below the gumline, the neck is formed. Below the neck, holding the tooth into the bone, is the root of the tooth. The inner portions of the tooth consist of the dentin, a bonelike tissue, and the pulp. The pulp is a soft tissue area containing the nerve and blood vessels to nourish and protect the tooth, located within the pulp cavity.

A tooth sits in a specialized socket called the alveolus. The tooth is held in location by a periodontal ligament, with the assistance of cementum. Teeth are surrounded by gingiva, or gums, part of the periodontium, support tissue of oral cavity protection. The periodontium includes all of the support membranes of the dental structures surround and support the teeth such as the gums and the attachment surfaces and membranes. These include epithelial tissues (epithelium), connective tissues, (ligaments and bone), muscle tissue and nervous tissue.

Salivary glands Edit

There are three sets of salivary glands: the parotid, the submandibular and the sublingual glands. The (exocrine) glands secrete saliva for proper mixing of food and provides enzymes to start chemical digestion. Saliva helps to hold together the formed bolus which is swallowed after chewing. Saliva is composed primarily of water, ions, salivary amylase, lysozymes, and trace amounts of urea.

Tongue Edit

The tongue is a specialized skeletal muscle that is specially adapted for the activities of speech, chewing, developing gustatory sense (taste) and swallowing. The tongue contains two sets of muscles, the intrinsic- involved with shape of tongue, and the extrinsic- involved with tongue movement. It is attached to the hyoid bone. Terms meaning tongue include "glosso" (from Greek) and "lingual" ((from Latin).

Nose Edit

Microanatomy Edit

The outer surfaces of the head and neck are lined by epithelium. The protective tissues of the oral cavity are continuous with the digestive tract are called mucosa or mucous membranes. The cells of the inner oral cavity are called the buccal mucosa.

The oral cavity is lined by a stratified squamous epithelium containing about three layers of cells. [ citation needed ] They line the oral, nasal, and external auditory meatus, (ear), providing lubrication and protection against pathogens.

The lips are also protected by specialized sensory cells called Meissner's corpuscles.

Blood supply Edit

Blood circulates from the upper systemic loop originating at the aortic arch, and includes: the brachiocephalic artery, left common carotid artery and left subclavian artery. The head and neck are emptied of blood by the subclavian vein and jugular vein.

The brachiocephalic artery or trunk is the first and largest artery that branches to form the right common carotid artery and the right subclavian artery. This artery provides blood to the right upper chest, right arm, neck, and head, through a branch called right vertebral artery. The right and left vertebral artery feed into the basilar artery and upward to the Posterior cerebral artery, which provides most of the brain with oxygenated blood. The posterior cerebral artery and the posterior communicating artery are within the circle of Willis.

The left common carotid artery divides to form the: internal carotid artery (ICA) and an external carotid artery (ECA). The ICA supplies the brain. The ECA supplies the neck and face.

The left subclavian artery and the right subclavian artery, one on each side of the body form the internal thoracic artery, the vertebral artery, the thyrocervical trunk, and the costocervical trunk. The subclavian becomes the axillary artery at the lateral border of the first rib. The left subclavian artery also provides blood to the left upper chest and left arm.

Blood–brain barrier Edit

The Blood–brain barrier (BBB) is semi-permeable membrane that controls the capillary leak potential of the circulatory system. In most parts of the body, the smallest blood vessels, called capillaries, are lined with endothelial cells, which have small spaces between each individual cell so substances can move readily between the inside and the outside of the capillary. This is not in the case of brain. In the brain, the endothelial cells fit tightly together to create a tight junction and substances cannot pass out of the bloodstream.

Specialized glial cells called astrocytes form a tight junction or protective barrier around brain blood vessels and may be important in the development of the BBB. Astrocytes may also be responsible for transporting ions (electrolytes) from the brain to the blood.

Venous drainage Edit

Blood from the brain and neck flows from: (1) within the cranium via the internal jugular veins, a continuation of the sigmoid sinuses. The right and left external jugular veins drain from the parotid glands, facial muscles, scalp into the subclavian veins. The right and left vertebral veins drain the vertebrae and muscles into the right subclavian vein and into the superior vena cava, into the right atrium of the heart.

Lymphatic system Edit

The lymphatic system drains the head and neck of excess interstitial fluid via lymph vessels or capillaries, equally into the right lymphatic duct and the thoracic duct.

Lymph nodes line the cervical spine and neck regions as well as along the face and jaw.

The tonsils also are lymphatic tissue and help mediate the ingestion of pathogens.

Tonsils in humans include, from superior to inferior: nasopharyngeal tonsils (also known as adenoids), palatine tonsils, and lingual tonsils.

Together this set of lymphatic tissue is called the tonsillar ring or Waldeyer's ring.

Nerve supply Edit

The spinal nerves arise from the spinal column. The top section of the spine is the cervical section, which contains nerves that innervate muscles of the head, neck and thoracic cavity, as well as transmit sensory information to the CNS.

The cervical spine section contains seven vertebrae, C-1 through C-7, and eight nerve pairs, C-1 through C-8.

There is the formation of an extensive network of nerve groups or tracts attaching to the spinal cord in arrangements called rami or plexus.

The sensory branches of spinal nerves include: lesser occipital, C-2, great auricular, (C-2 and C-3) transverse cervical, C-2 and C-3 and supraclavicular, C-3 and C-4. These nerve groups transmit afferent (sensory) information from the scalp, neck, and shoulders to the brain.

The motor branches of spinal nerves include: ansa cervicalis, dividing into a superior root, C-1, and an inferior root, C-2 and C-3, and the phrenic nerve, C-3 to C-5, the segmental nerve branches, C-1 to C-5. These nerve groups transmit efferent nerve (motor) information from the brain to muscle groups of the scalp, neck, diaphragm (anatomy), and shoulders.

Additionally there are: (C5-C8, and T1) Brachial plexus, providing the entire nerve supply of the shoulder and upper limb and includes supraclavicular branches (dorsal scapular, suprascapular, long thoracic) lateral cord (musculocutaneous, lateral antibrachial cutaneous, lateral head of median nerve), medial cord (ulnar, medial head of median nerve, medial antibrachial cutaneous, medial brachial cutaneous), posterior cord (axillary, radial), controlling the arm.

Damage to a person's spinal cord above C-5 may result in respiratory arrest and death if medicinal aid does not intervene.

Cranial nerves Edit

Twelve pairs of cranial nerves emerge from the brain these affect movements and sensation, and some special organs such as hearing of parts of the head and neck.

Movements of the neck includes: flexion, extension, (nodding yes), and rotation (shaking head no).

The mouth has evolved to support chewing, (mastication) and swallowing (deglutition), and speech (phonation).

In addition to the teeth, other structures that aid chewing are the lips, cheeks, tongue, hard palate, soft palate, and floor of the mouth.

Endocrine glands Edit

Several glands of the endocrine system are found within the head and neck. Endocrine means that the secretion is used within the body. Endocrine glands are termed as ductless and release their secretions directly into the blood. The endocrine system is under the direct supervision of the nervous system, using the negative feedback principal of homeostasis, to create hormones which act as chemical instant messengers.

The hypothalamus connects directly to the pituitary gland, both through the circulatory system and by direct connection of neurons. Also, within the cranium, the pineal gland, which attaches to the thalamus, controls the body's 24-hour rhythms circadian rhythm through the release of melatonin.

The pituitary gland secretes hormones that directly impact the body as well as hormones that indirectly control body functions because they activate other endocrine glands, such as the adrenal cortex (ACTH) and the thyroid gland (TSH). These two glands when stimulated by pituitary hormones then release their own hormones. The pituitary gland has two lobes, the anterior lobe and the posterior lobe. The anterior lobe secretes: growth hormone (GH), Luteinizing hormone (LH), Follicle stimulating hormone (FSH), Adrenocorticotropic hormone (ACTH), Thyroid-stimulating hormone (TSH), Prolactin (PRL), and the posterior lobe secretes: Antidieuretic hormone (ADH), and Oxytocin. There is an intermediate lobe, in adult humans it is just a thin layer of cells between the anterior and posterior pituitary, nearly indistinguishable from the anterior lobe. The intermediate lobe produces melanocyte-stimulating hormone (MSH).

In the neck are the thyroid and parathyroid glands, that secrete hormones that control metabolism and blood calcium levels. The four parathyroid glands are situated upon the back surface of the thyroid gland.

Respiratory system Edit

The respiratory system begins in the head and neck, with air entering and leaving the body through the mouth and nose. The respiratory system involving the head and neck includes:

  1. the nasal cavity for filtering, moistening, and warming the air
  2. the pharynx or throat which is the combining point for respiratory and digestive system
  3. the larynx or voice box containing the epiglottis
  4. the trachea, or windpipe

These lead down into the lower respiratory tract. A critical junction between the respiratory and digestive systems is the epiglottis, a cartilage flap which shuts during swallowing to prevent aspiration. The epiglottis is normally open to support respiration and shuts during swallowing to prevent food and fluids from entering the trachea, activating the gag reflex or initiates the choking mechanism.

Central nervous system Edit

The nervous system is composed of a central nervous system (CNS), brain and spinal cord, and the peripheral nervous system (PNS), cranial nerves and spinal nerves. The CNS is located within the dorsal cavity, and the PNS extends through the ventral cavity. The central nervous system provides control and coordination of all eleven body systems and utilizes the endocrine system to form hormone chemical messengers that transport through the blood to influence the activity of individual cells of the body and their associated tissues, organs and systems.

The CNS receives sensory (afferent) input from the PNS and directs the flow of information to association neurons (interneurons) to create chemical synapse responses which in turn cause the formation of motor (efferent nerve) responses to stimulus. Association neurons are located in the grey matter of the spinal cord and the brain.

The CNS is protected by the cranium, vertebral column, meninges, cerebrospinal fluid. The spinal cord is an extension of the brain. The spinal cord and the brain stem are joined at the base of the cranium at the foramen magnum. Most of the functions of the head and neck are directly influenced by the brain and transmitted to the PNS via the cranial nerves and spinal nerves of the cervical portion of the spine.

The PNS has two subdivisions

    (SNS). The SNS is associated with the voluntary control of body movements through the action of skeletal muscles, and also the reception of external stimuli.
  • the autonomic nervous system (ANS). The ANS is divided into subsystems: the sympathetic nervous system (SNS) and the parasympathetic (PNS) nervous systems. The SNS and PNS often have opposing effects in the same organs or physiological systems, and the ANS is a major factor in maintaining homeostasis.

Bones Edit

The facial bones usually form into pairs and then fuse together. As the cranium fuses, sutures are formed that resemble stitching between bone plates. In a newborn, the junction of the parietal bones with the frontal and occipital bones, form the anterior (front) and posterior (back) fontanelle, or soft spots. The separation of the cranial bone plates at time of birth facilitate passage of the head of the fetus through the mother's birth canal, or pelvic girdle. The parietal bones, and occipital bone can overlap each other in the birth canal, and form the unusual looking "cone head" appearance in a newborn when delivered in a natural, or vaginal, delivery.

Teeth Edit

Humans normally will produce two sets of teeth called primary dentition, or deciduous teeth, and secondary dentition, or permanent teeth.

A tooth is the toughest known substance in the body exceeding bones in density and strength. Tooth enamel lends great strength to the tooth structure. The formation of a developing tooth includes the process of dentin formation, (see: Dentinogenesis) and enamel formation, (see: amelogenesis). The tooth breaks through the gum into the mouth in a process called eruption. The formation of teeth begins in early fetal development and goes through six stages:

  • (1) initiation stage, 6th - 7th week
  • (2) bud stage, 8th wk
  • (3) cap stage, 9th-10 wk
  • (4) bell stage, 11th-12th wk
  • (5) apposition
  • (6) maturation stage

Infection Edit

Severe viral infections that affect the mouth, lips, or the oral cavity include: Oral cancer may have a viral link.

  1. Minor viral infections include: Mumps is a viral infection of the parotid salivary glands. Chicken pox is a viral infection that can spread to the mouth.
  2. Thrush (Candidiasis) fungal infection. Tonsillitis is an inflammation of the tonsils and may cause a sore throat and fever. In chronic cases tonsillectomy may be required.

Infected teeth can on rare occasions cause infection to spread leading to cavernous sinus thrombosis, mediastinitis, or Ludwig's angina causing airway blockage.

Diseases may be transmitted by contact of the head, mouth, or body fluids, such as Herpes Simplex Virus Type I (HSV-1), Herpes Simplex Virus Type II (HSV-2) genital herpes, which may present as a lesion on the lips, and contactable via skin to skin contact

Other Edit

  1. Other diseases include: Gingivitis gum disease, periodontal disease, oral forms of syphilis and gonorrhea. Dental caries or dental cavities. diseases and disorders, commonly called TMJ.
  2. Autoimmune diseases such as: Crohn's disease of the oral cavity, see reference below.

Careful observation of the oral cavity, teeth and gums may reveal indicators of other medical conditions. For example, a person suffering from the eating disorder, Bulimia nervosa may show signs of excessive tooth and gum erosion.

Airway obstruction Edit

The airway in the head and neck may be obstructed with swelling associated with an enlarged tongue (macroglossia), tonsils, with swelling associated with anaphylactic shock, angiooedema, or a foreign body.

Anaphylactic shock requires advanced medical care immediately but other first aid measures include rescue breathing (part of CPR) and administration of epinephrine using an EpiPen for immediate administration of epinephrine (adrenaline) to reverse swelling and to keep the respiratory airway (trachea) open.


Bones

Bones from the skeleton of the body. There are more than 200 separate bones forming the skeleton. The study of bone is called “Osteology”. many blood cells — red blood cells, white blood cells, and platelets — are formed within your bones, This process is called hematopoiesis, and it occurs in the red marrow.

The skeleton

  1. Axial skeleton: Skull, Vertebra, Sternum, and Ribs.
  2. Appendicular skeleton: Bones of Upper limb: ( pectoral girdle, Bone of arm, Bones of the forearm, Bones of hand), Bones of the lower limb: ( Pelvic girdle, bone of the thigh, Bones of the leg, and bones of the foot).

Bones are divided according to their shape into:

  1. Long bones such as humerus, femur, and radius.
  2. Short bones such as metacarpal bones.
  3. Flat bones such as scapula or ilium.
  4. Irregular bones such as vertebrae.
  5. Pneumatic bones such as the skull.
  6. Sesamoid bones such as patella.

The humerus is the bone of the arm. It is one of the long bones. Each long bone has an upper end, shaft, and lower end. The metacarpal bones form the skeleton of the palm of the hand. They are examples of short bones as they have the same parts as the long bone but they are small in size. The patella in front of the knee joint is an example of the sesamoid bone.

Each long bone has a growing end (that ossifies later) and a non-growing end. The growing end of the humerus is the upper end. The growing ends of the radius and ulna are the lower ends. As for the bones of the lower limb is the opposite. This means that the growing end of the femur is the lower end whereas the growing ends of the tibia and the fibula are the upper ends.

Nutrient Artery

Each bone is capable of growth and repair. Thus, each bone receives its nutrient artery. It enters the bone at a certain place and in a certain direction. The nutrient artery in the long bones is directed towards the non-growing end. Thus in the humerus, it runs towards the lower end of the bone or the elbow.

Parts of a Growing Long Bone:

  • A long bone consists of two ends and a shaft.
  • Each end is called an epiphysis.
  • The shaft is called the diaphysis.
  • In a growing bone, the epiphysis is separated from the diaphysis by a plate of cartilage, an epiphyseal plate. This epiphyseal plate is the site of an increase in the length of the bone. The region of the shaft close to the epiphyseal plate is called metaphysis. At a certain age, when growth is completed, these plates ossify.
  • The shaft of a long bone is formed of compact bone enclosing a cavity which is filled with bone marrow. This cavity is called: a medullary cavity or a bone marrow cavity.
  • The epiphysis is formed of spongy, cancellous bone.
  • The shaft is covered by a fibrous membrane: the periosteum.
  • The parts of the bone that articulate are covered with hyaline articular cartilage.

Functions of Bones

  1. Bones form the supporting frame-work of the body.
  2. Bones protect the underlying structures, e.g. the skull protects the brain.
  3. Bones give attachments to the muscles and also act as levers for movement.
  4. Bones store calcium and phosphorus.
  5. The bone marrow acts as a factory for the formation of blood cells.

There are sex differences between male and female bones. Usually, the male bones are loner, heavier thicker, stronger, and possess prominent impressions for muscular attachments.

Applied Anatomy

Osteoporosis: It is the most common bone disease. It affects more the elderly white woman. The bones lose their mass and become brittle and subject to fracture. Milk and other calcium sources and moderate exercise can slow the progress of osteoporosis.

Bone fractures: Bone is a living tissue. When it is fractured it heals by callus formation. Fractures result from accidents. Patients with osteoporosis are more liable to fractures. The most common fracture in elderly is the fracture neck femur.

The vertebral column

The vertebral column (backbone or spine) is a midline column formed of 33 Vertebrae separated by intervertebral cartilaginous discs. It houses and protects the spinal cord in its spinal canal. In the side view, the vertebral column presents several curves, which correspond to the different regions of the column.

Curvature of the Spine in Adults

The shape of a normal adult human spine has 4 curves:

  1. Cervical curve: formed by 7 cervical vertebrae.
  2. Thoracic curve: formed by 12 thoracic vertebrae.
  3. Lumbar curve: formed by 5 lumbar vertebrae.
  4. Sacral curve: formed by 5 sacral vertebrae.

All vertebrae share a basic common structure. Each consists of a vertebral body, situated anteriorly, and a posterior vertebral arch.

Vertebral body

The vertebral body is the anterior part of the vertebrae. It is the weight-bearing component and its size increases as the vertebral column descends (having to support increasing amounts of weight.

Vertebral Arch

The vertebral arch refers to the lateral and posterior parts of the vertebrae. With the vertebral body, the vertebral arch forms an enclosed hole, called a vertebral foramen. The foramina of all vertebrae line up form the vertebral canal, which encloses the spinal cord. The vertebral arches have a number of bony prominences, which act as attachment sites for muscles and ligaments:

  • Pedicles: There are two of these, one left and one right. They point posteriorly, meeting the laminae.
  • Lamina: The bone between the transverse and spinous processes.
  • Transverse processes: These extend laterally and posteriorly away from the pedicles. In the thoracic vertebrae, the transverse processes articulate with the ribs.
  • Articular processes: At the junction of the lamina and the pedicles, superior and inferior processes arise. These articulate with the articular processes of the vertebrae above and below.
  • Spinous processes: Posterior and inferior projection of bone, a site of attachment for muscles and ligaments.

Thoracic Vertebrae

Sacrum and Coccyx

The sacrum is a collection of five fused vertebrae. It is described as an inverted triangle, with the apex pointing inferiorly. On the lateral walls of the sacrum are facets, for articulation with the pelvis at the sacroiliac joints.

The coccyx is a small bone, which articulates with the apex of the sacrum. It is recognized by its lack of vertebral arches. Due to the lack of vertebral arches, there is no vertebral canal, and so the coccyx does not transmit the spinal cord.


Microscopic Anatomy of The Compact Bone

Figure (PageIndex<4>): Macroscopic and microscopic structures of the compact bone tissue.

The basic microscopic unit of bone is an osteon (or Haversian system). Osteons are roughly cylindrical structures that can measure several millimeters long and around 0.2 mm in diameter. Each osteon consists of lamellae of compact bone tissue that surround a central canal (Haversian canal). The Haversian canal contains the bone's blood supplies. The boundary of an osteon is called the cement line. Osteons can be arranged into woven bone or lamellar bone. Osteoblasts make the matrix of bone which calcifies hardens. This entraps the mature bone cells, osteocytes, in a little chamber called lacunae. The osteocytes receive their nutrition from the central (Haversian) canal via little canals called canaliculi. All of these structures plus more are visible in Figure (PageIndex<4>).


Skeletal system 1: the anatomy and physiology of bones

The skeletal system is formed of bones and cartilage, which are connected by ligaments to form a framework for the remainder of the body tissues. This article, the first in a two-part series on the structure and function of the skeletal system, reviews the anatomy and physiology of bone. Understanding the structure and purpose of the bone allows nurses to understand common pathophysiology and consider the most-appropriate steps to improve musculoskeletal health.

Citation: Walker J (2020) Skeletal system 1: the anatomy and physiology of bones. Nursing Times [online] 116: 2, 38-42.

Author: Jennie Walker is principal lecturer, Nottingham Trent University.

  • This article has been double-blind peer reviewed
  • Scroll down to read the article or download a print-friendly PDF here (if the PDF fails to fully download please try again using a different browser)
  • Read part 2 of this series here

Introduction

The skeletal system is composed of bones and cartilage connected by ligaments to form a framework for the rest of the body tissues. There are two parts to the skeleton:

  • Axial skeleton – bones along the axis of the body, including the skull, vertebral column and ribcage
  • Appendicular skeleton – appendages, such as the upper and lower limbs, pelvic girdle and shoulder girdle.

Function

As well as contributing to the body’s overall shape, the skeletal system has several key functions, including:

  • Support and movement
  • Protection
  • Mineral homeostasis
  • Blood-cell formation
  • Triglyceride storage.

Support and movement

Bones are a site of attachment for ligaments and tendons, providing a skeletal framework that can produce movement through the coordinated use of levers, muscles, tendons and ligaments. The bones act as levers, while the muscles generate the forces responsible for moving the bones.

Protection

Bones provide protective boundaries for soft organs: the cranium around the brain, the vertebral column surrounding the spinal cord, the ribcage containing the heart and lungs, and the pelvis protecting the urogenital organs.

Mineral homoeostasis

As the main reservoirs for minerals in the body, bones contain approximately 99% of the body’s calcium, 85% of its phosphate and 50% of its magnesium (Bartl and Bartl, 2017). They are essential in maintaining homoeostasis of minerals in the blood with minerals stored in the bone are released in response to the body’s demands, with levels maintained and regulated by hormones, such as parathyroid hormone.

Blood-cell formation (haemopoiesis)

Blood cells are formed from haemopoietic stem cells present in red bone marrow. Babies are born with only red bone marrow over time this is replaced by yellow marrow due to a decrease in erythropoietin, the hormone responsible for stimulating the production of erythrocytes (red blood cells) in the bone marrow. By adulthood, the amount of red marrow has halved, and this reduces further to around 30% in older age (Robson and Syndercombe Court, 2018).

Triglyceride storage

Yellow bone marrow (Fig 1) acts as a potential energy reserve for the body it consists largely of adipose cells, which store triglycerides (a type of lipid that occurs naturally in the blood) (Tortora and Derrickson, 2009).

Bone composition

Bone matrix has three main components:

  • 25% organic matrix (osteoid)
  • 50% inorganic mineral content (mineral salts)
  • 25% water (Robson and Syndercombe Court, 2018).

Organic matrix (osteoid) is made up of approximately 90% type-I collagen fibres and 10% other proteins, such as glycoprotein, osteocalcin, and proteoglycans (Bartl and Bartl, 2017). It forms the framework for bones, which are hardened through the deposit of the calcium and other minerals around the fibres (Robson and Syndercombe Court, 2018).

Mineral salts are first deposited between the gaps in the collagen layers with once these spaces are filled, minerals accumulate around the collagen fibres, crystallising and causing the tissue to harden this process is called ossification (Tortora and Derrickson, 2009). The hardness of the bone depends on the type and quantity of the minerals available for the body to use hydroxyapatite is one of the main minerals present in bones.

While bones need sufficient minerals to strengthen them, they also need to prevent being broken by maintaining sufficient flexibility to withstand the daily forces exerted on them. This flexibility and tensile strength of bone is derived from the collagen fibres. Over-mineralisation of the fibres or impaired collagen production can increase the brittleness of bones – as with the genetic disorder osteogenesis imperfecta – and increase bone fragility (Ralston and McInnes, 2014).

Structure

Bone architecture is made up of two types of bone tissue:

Cortical bone

Also known as compact bone, this dense outer layer provides support and protection for the inner cancellous structure. Cortical bone comprises three elements:

The periosteum is a tough, fibrous outer membrane. It is highly vascular and almost completely covers the bone, except for the surfaces that form joints these are covered by hyaline cartilage. Tendons and ligaments attach to the outer layer of the periosteum, whereas the inner layer contains osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells) responsible for bone remodelling.

The function of the periosteum is to:

  • Protect the bone
  • Help with fracture repair
  • Nourish bone tissue (Robson and Syndercombe Court, 2018).

It also contains Volkmann’s canals, small channels running perpendicular to the diaphysis of the bone (Fig 1) these convey blood vessels, lymph vessels and nerves from the periosteal surface through to the intracortical layer. The periosteum has numerous sensory fibres, so bone injuries (such as fractures or tumours) can be extremely painful (Drake et al, 2019).

The intracortical bone is organised into structural units, referred to as osteons or Haversian systems (Fig 2). These are cylindrical structures, composed of concentric layers of bone called lamellae, whose structure contributes to the strength of the cortical bone. Osteocytes (mature bone cells) sit in the small spaces between the concentric layers of lamellae, which are known as lacunae. Canaliculi are microscopic canals between the lacunae, in which the osteocytes are networked to each other by filamentous extensions. In the centre of each osteon is a central (Haversian) canal through which the blood vessels, lymph vessels and nerves pass. These central canals tend to run parallel to the axis of the bone Volkmann’s canals connect adjacent osteons and the blood vessels of the central canals with the periosteum.

The endosteum consists of a thin layer of connective tissue that lines the inside of the cortical surface (Bartl and Bartl, 2017) (Fig 1).

Cancellous bone

Also known as spongy bone, cancellous bone is found in the outer cortical layer. It is formed of lamellae arranged in an irregular lattice structure of trabeculae, which gives a honeycomb appearance. The large gaps between the trabeculae help make the bones lighter, and so easier to mobilise.

Trabeculae are characteristically oriented along the lines of stress to help resist forces and reduce the risk of fracture (Tortora and Derrickson, 2009). The closer the trabecular structures are spaced, the greater the stability and structure of the bone (Bartl and Bartl, 2017). Red or yellow bone marrow exists in these spaces (Robson and Syndercombe Court, 2018). Red bone marrow in adults is found in the ribs, sternum, vertebrae and ends of long bones (Tortora and Derrickson, 2009) it is haemopoietic tissue, which produces erythrocytes, leucocytes (white blood cells) and platelets.

Blood supply

Bone and marrow are highly vascularised and account for approximately 10-20% of cardiac output (Bartl and Bartl, 2017). Blood vessels in bone are necessary for nearly all skeletal functions, including the delivery of oxygen and nutrients, homoeostasis and repair (Tomlinson and Silva, 2013). The blood supply in long bones is derived from the nutrient artery and the periosteal, epiphyseal and metaphyseal arteries (Iyer, 2019).

Each artery is also accompanied by nerve fibres, which branch into the marrow cavities. Arteries are the main source of blood and nutrients for long bones, entering through the nutrient foramen, then dividing into ascending and descending branches. The ends of long bones are supplied by the metaphyseal and epiphyseal arteries, which arise from the arteries from the associated joint (Bartl and Bartl, 2017).

If the blood supply to bone is disrupted, it can result in the death of bone tissue (osteonecrosis). A common example is following a fracture to the femoral neck, which disrupts the blood supply to the femoral head and causes the bone tissue to become necrotic. The femoral head structure then collapses, causing pain and dysfunction.

Growth

Bones begin to form in utero in the first eight weeks following fertilisation (Moini, 2019). The embryonic skeleton is first formed of mesenchyme (connective tissue) structures this primitive skeleton is referred to as the skeletal template. These structures are then developed into bone, either through intramembranous ossification or endochondral ossification (replacing cartilage with bone).

Bones are classified according to their shape (Box 1). Flat bones develop from membrane (membrane models) and sesamoid bones from tendon (tendon models) (Waugh and Grant, 2018). The term intra-membranous ossification describes the direct conversion of mesenchyme structures to bone, in which the fibrous tissues become ossified as the mesenchymal stem cells differentiate into osteoblasts. The osteoblasts then start to lay down bone matrix, which becomes ossified to form new bone.

Box 1. Types of bones

Long bones – typically longer than they are wide (such as humerus, radius, tibia, femur), they comprise a diaphysis (shaft) and epiphyses at the distal and proximal ends, joining at the metaphysis. In growing bone, this is the site where growth occurs and is known as the epiphyseal growth plate. Most long bones are located in the appendicular skeleton and function as levers to produce movement

Short bones – small and roughly cube-shaped, these contain mainly cancellous bone, with a thin outer layer of cortical bone (such as the bones in the hands and tarsal bones in the feet)

Flat bones – thin and usually slightly curved, typically containing a thin layer of cancellous bone surrounded by cortical bone (examples include the skull, ribs and scapula). Most are located in the axial skeleton and offer protection to underlying structures

Irregular bones – bones that do not fit in other categories because they have a range of different characteristics. They are formed of cancellous bone, with an outer layer of cortical bone (for example, the vertebrae and the pelvis)

Sesamoid bones – round or oval bones (such as the patella), which develop in tendons

Long, short and irregular bones develop from an initial model of hyaline cartilage (cartilage models). Once the cartilage model has been formed, the osteoblasts gradually replace the cartilage with bone matrix through endochondral ossification (Robson and Syndercombe Court, 2018). Mineralisation starts at the centre of the cartilage structure, which is known as the primary ossification centre. Secondary ossification centres also form at the epiphyses (epiphyseal growth plates) (Danning, 2019). The epiphyseal growth plate is composed of hyaline cartilage and has four regions (Fig 3):

Resting or quiescent zone – situated closest to the epiphysis, this is composed of small scattered chondrocytes with a low proliferation rate and anchors the growth plate to the epiphysis

Growth or proliferation zone – this area has larger chondrocytes, arranged like stacks of coins, which divide and are responsible for the longitudinal growth of the bone

Hypertrophic zone – this consists of large maturing chondrocytes, which migrate towards the metaphysis. There is no new growth at this layer

Calcification zone – this final zone of the growth plate is only a few cells thick. Through the process of endochondral ossification, the cells in this zone become ossified and form part of the ‘new diaphysis’ (Tortora and Derrickson, 2009).

Bones are not fully developed at birth, and continue to form until skeletal maturity is reached. By the end of adolescence around 90% of adult bone is formed and skeletal maturity occurs at around 20-25 years, although this can vary depending on geographical location and socio-economic conditions for example, malnutrition may delay bone maturity (Drake et al, 2019 Bartl and Bartl, 2017). In rare cases, a genetic mutation can disrupt cartilage development, and therefore the development of bone. This can result in reduced growth and short stature and is known as achondroplasia.

The human growth hormone (somatotropin) is the main stimulus for growth at the epiphyseal growth plates. During puberty, levels of sex hormones (oestrogen and testosterone) increase, which stops cell division within the growth plate. As the chondrocytes in the proliferation zone stop dividing, the growth plate thins and eventually calcifies, and longitudinal bone growth stops (Ralston and McInnes, 2014). Males are on average taller than females because male puberty tends to occur later, so male bones have more time to grow (Waugh and Grant, 2018). Over-secretion of human growth hormone during childhood can produce gigantism, whereby the person is taller and heavier than usually expected, while over-secretion in adults results in a condition called acromegaly.

If there is a fracture in the epiphyseal growth plate while bones are still growing, this can subsequently inhibit bone growth, resulting in reduced bone formation and the bone being shorter. It may also cause misalignment of the joint surfaces and cause a predisposition to developing secondary arthritis later in life. A discrepancy in leg length can lead to pelvic obliquity, with subsequent scoliosis caused by trying to compensate for the difference.

Remodelling

Once bone has formed and matured, it undergoes constant remodelling by osteoclasts and osteoblasts, whereby old bone tissue is replaced by new bone tissue (Fig 4). Bone remodelling has several functions, including mobilisation of calcium and other minerals from the skeletal tissue to maintain serum homoeostasis, replacing old tissue and repairing damaged bone, as well as helping the body adapt to different forces, loads and stress applied to the skeleton.

Calcium plays a significant role in the body and is required for muscle contraction, nerve conduction, cell division and blood coagulation. As only 1% of the body’s calcium is in the blood, the skeleton acts as storage facility, releasing calcium in response to the body’s demands. Serum calcium levels are tightly regulated by two hormones, which work antagonistically to maintain homoeostasis. Calcitonin facilitates the deposition of calcium to bone, lowering the serum levels, whereas the parathyroid hormone stimulates the release of calcium from bone, raising the serum calcium levels.

Osteoclasts are large multinucleated cells typically found at sites where there is active bone growth, repair or remodelling, such as around the periosteum, within the endosteum and in the removal of calluses formed during fracture healing (Waugh and Grant, 2018). The osteoclast cell membrane has numerous folds that face the surface of the bone and osteoclasts break down bone tissue by secreting lysosomal enzymes and acids into the space between the ruffled membrane (Robson and Syndercombe Court, 2018). These enzymes dissolve the minerals and some of the bone matrix. The minerals are released from the bone matrix into the extracellular space and the rest of the matrix is phagocytosed and metabolised in the cytoplasm of the osteoclasts (Bartl and Bartl, 2017). Once the area of bone has been resorbed, the osteoclasts move on, while the osteoblasts move in to rebuild the bone matrix.

Osteoblasts synthesise collagen fibres and other organic components that make up the bone matrix. They also secrete alkaline phosphatase, which initiates calcification through the deposit of calcium and other minerals around the matrix (Robson and Syndercombe Court, 2018). As the osteoblasts deposit new bone tissue around themselves, they become trapped in pockets of bone called lacunae. Once this happens, the cells differentiate into osteocytes, which are mature bone cells that no longer secrete bone matrix.

The remodelling process is achieved through the balanced activity of osteoclasts and osteoblasts. If bone is built without the appropriate balance of osteocytes, it results in abnormally thick bone or bony spurs. Conversely, too much tissue loss or calcium depletion can lead to fragile bone that is more susceptible to fracture. The larger surface area of cancellous bones is associated with a higher remodelling rate than cortical bone (Bartl and Bartl, 2017), which means osteoporosis is more evident in bones with a high proportion of cancellous bone, such as the head/neck of femur or vertebral bones (Robson and Syndercombe Court, 2018). Changes in the remodelling balance may also occur due to pathological conditions, such as Paget’s disease of bone, a condition characterised by focal areas of increased and disorganised bone remodelling affecting one or more bones. Typical features on X-ray include focal patches of lysis or sclerosis, cortical thickening, disorganised trabeculae and trabecular thickening.

As the body ages, bone may lose some of its strength and elasticity, making it more susceptible to fracture. This is due to the loss of mineral in the matrix and a reduction in the flexibility of the collagen.

Diet and lifestyle factors

Adequate intake of vitamins and minerals is essential for optimum bone formation and ongoing bone health. Two of the most important are calcium and vitamin D, but many others are needed to keep bones strong and healthy (Box 2).

Box 2. Vitamins and minerals needed for bone health

Key nutritional requirements for bone health include minerals such as calcium and phosphorus, as well as smaller qualities of fluoride, manganese, and iron (Robson and Syndercombe Court, 2018). Calcium, phosphorus and vitamin D are essential for effective bone mineralisation. Vitamin D promotes calcium absorption in the intestines, and deficiency in calcium or vitamin D can predispose an individual to ineffective mineralisation and increased risk of developing conditions such as osteoporosis and osteomalacia.

Other key vitamins for healthy bones include vitamin A for osteoblast function and vitamin C for collagen synthesis (Waugh and Grant, 2018).

Physical exercise, in particular weight-bearing exercise, is important in maintaining or increasing bone mineral density and the overall quality and strength of the bone. This is because osteoblasts are stimulated by load-bearing exercise and so bones subjected to mechanical stresses undergo a higher rate of bone remodelling. Reduced skeletal loading is associated with an increased risk of developing osteoporosis (Robson and Syndercombe Court, 2018).

Conclusion

Bones are an important part of the musculoskeletal system and serve many core functions, as well as supporting the body’s structure and facilitating movement. Bone is a dynamic structure, which is continually remodelled in response to stresses placed on the body. Changes to this remodelling process, or inadequate intake of nutrients, can result in changes to bone structure that may predispose the body to increased risk of fracture. Part 2 of this series will review the structure and function of the skeletal system.

Key points

  • Bones are key to providing the body with structural support and enabling movement
  • Most of the body’s minerals are stored in the bones
  • Diet and lifestyle can affect the quality of bone formation
  • After bones have formed they undergo constant remodelling
  • Changes in the remodelling process can result in pathology such as Paget’s disease of bone or osteoporosis

Bartl R, Bartl C (2017) Structure and architecture of bone. In: Bone Disorder: Biology, Diagnosis, Prevention, Therapy.

Danning CL (2019) Structure and function of the musculoskeletal system. In: Banasik JL, Copstead L-EC (eds) Pathophysiology. St Louis, MO: Elsevier.

Drake RL et al (eds) (2019) Gray’s Anatomy for Students. London: Elsevier.

Iyer KM (2019) Anatomy of bone, fracture, and fracture healing. In: Iyer KM, Khan WS (eds) General Principles of Orthopedics and Trauma. London: Springer.

Moini J (2019) Bone tissues and the skeletal system. In: Anatomy and Physiology for Health Professionals. Burlington, MA: Jones and Bartlett.

Ralston SH, McInnes IB (2014) Rheumatology and bone disease. In: Walker BR et al (eds) Davidson’s Principles and Practice of Medicine. Edinburgh: Churchill Livingstone.

Robson L, Syndercombe Court D (2018) Bone, muscle, skin and connective tissue. In: Naish J, Syndercombe Court D (eds) Medical Sciences. London: Elsevier

Tomlinson RE, Silva MJ (2013) Skeletal blood flow in bone repair and maintenance. Bone Research 1: 4, 311-322.

Tortora GJ, Derrickson B (2009) The skeletal system: bone tissue. In: Principles of Anatomy and Physiology. Chichester: John Wiley & Sons.

Waugh A, Grant A (2018) The musculoskeletal system. In: Ross & Wilson Anatomy and Physiology in Health and Illness. London: Elsevier.


Difference Between Diaphysis Epiphysis

Epiphysis meaning - It is the end part of a long bone, initially growing separate from the shaft.

Diaphysis meaning - It is the shaft or central part of a long bone.

It makes up the swollen rounded ends of the long bone.

It makes up the long and narrow region of the long bone.

Two epiphyses occur at the proximal and the distal end of the long bone

Single diaphysis occurs per long bone

Epiphysis of bone is made up of spongy bone

The diaphysis of bone is made of cortical bone

The functional unit is Trabecula

The functional unit is the osteon

Contains a red bone marrow

Contains a yellow bone marrow

Contains less amount of calcium

Contains a higher amount of calcium

Articulate with other bones forming joints

Provides sites for the attachment of bones

Do You Know?

What are the epiphyseal plate and epiphyseal line? Epiphyseal plate Definition - The epiphyseal plate (also known as the epiphysial plate, physic, or growth plate) is a hyaline cartilage plate found at either end of a long bone in the metaphysis. The growth plate is the portion of a long bone where new bone growth occurs the whole bone is alive, with maintenance remodeling occurring in its current bone tissue, but the growth plate is where the long bone grows larger (adds length).

Epiphyseal Line Definition - An ossified epiphyseal plate is referred to as an epiphyseal line. Epiphyseal closure is the process by which the formation of an epiphyseal layer takes place. It is the point of fusion between the Epiphysis and the Diaphysis in adult humans.


The Skeleton

The adult human skeleton has a total of 213 bones, excluding the sesamoid bones (1). The appendicular skeleton has 126 bones, axial skeleton 74 bones, and auditory ossicles six bones. Each bone constantly undergoes modeling during life to help it adapt to changing biomechanical forces, as well as remodeling to remove old, microdamaged bone and replace it with new, mechanically stronger bone to help preserve bone strength.

The four general categories of bones are long bones, short bones, flat bones, and irregular bones. Long bones include the clavicles, humeri, radii, ulnae, metacarpals, femurs, tibiae, fibulae, metatarsals, and phalanges. Short bones include the carpal and tarsal bones, patellae, and sesamoid bones. Flat bones include the skull, mandible, scapulae, sternum, and ribs. Irregular bones include the vertebrae, sacrum, coccyx, and hyoid bone. Flat bones form by membranous bone formation, whereas long bones are formed by a combination of endochondral and membranous bone formation.

The skeleton serves a variety of functions. The bones of the skeleton provide structural support for the rest of the body, permit movement and locomotion by providing levers for the muscles, protect vital internal organs and structures, provide maintenance of mineral homeostasis and acid-base balance, serve as a reservoir of growth factors and cytokines, and provide the environment for hematopoiesis within the marrow spaces (2).

The long bones are composed of a hollow shaft, or diaphysis flared, cone-shaped metaphyses below the growth plates and rounded epiphyses above the growth plates. The diaphysis is composed primarily of dense cortical bone, whereas the metaphysis and epiphysis are composed of trabecular meshwork bone surrounded by a relatively thin shell of dense cortical bone.

The adult human skeleton is composed of 80% cortical bone and 20% trabecular bone overall (3). Different bones and skeletal sites within bones have different ratios of cortical to trabecular bone. The vertebra is composed of cortical to trabecular bone in a ratio of 25:75. This ratio is 50:50 in the femoral head and 95:5 in the radial diaphysis.

Cortical bone is dense and solid and surrounds the marrow space, whereas trabecular bone is composed of a honeycomb-like network of trabecular plates and rods interspersed in the bone marrow compartment. Both cortical and trabecular bone are composed of osteons.

Cortical osteons are called Haversian systems. Haversian systems are cylindrical in shape, are approximately 400 mm long and 200 mm wide at their base, and form a branching network within the cortical bone (3). The walls of Haversian systems are formed of concentric lamellae. Cortical bone is typically less metabolically active than trabecular bone, but this depends on the species. There are an estimated 21 × 10 6 cortical osteons in healthy human adults, with a total Haversian remodeling area of approximately 3.5 m 2 . Cortical bone porosity is usually υ%, but this depends on the proportion of actively remodeling Haversian systems to inactive cortical osteons. Increased cortical remodeling causes an increase in cortical porosity and decrease in cortical bone mass. Healthy aging adults normally experience thinning of the cortex and increased cortical porosity.

Cortical bone has an outer periosteal surface and inner endosteal surface. Periosteal surface activity is important for appositional growth and fracture repair. Bone formation typically exceeds bone resorption on the periosteal surface, so bones normally increase in diameter with aging. The endosteal surface has a total area of approximately 0.5 m 2 , with higher remodeling activity than the periosteal surface, likely as a result of greater biomechanical strain or greater cytokine exposure from the adjacent bone marrow compartment. Bone resorption typically exceeds bone formation on the endosteal surface, so the marrow space normally expands with aging.

Trabecular osteons are called packets. Trabecular bone is composed of plates and rods averaging 50 to 400 mm in thickness (3). Trabecular osteons are semilunar in shape, normally approximately 35 mm thick, and composed of concentric lamellae. It is estimated that there are 14 × 10 6 trabecular osteons in healthy human adults, with a total trabecular area of approximately 7 m 2 .

Cortical bone and trabecular bone are normally formed in a lamellar pattern, in which collagen fibrils are laid down in alternating orientations (3). Lamellar bone is best seen during microscopic examination with polarized light, during which the lamellar pattern is evident as a result of birefringence. The mechanism by which osteoblasts lay down collagen fibrils in a lamellar pattern is not known, but lamellar bone has significant strength as a result of the alternating orientations of collagen fibrils, similar to plywood. The normal lamellar pattern is absent in woven bone, in which the collagen fibrils are laid down in a disorganized manner. Woven bone is weaker than lamellar bone. Woven bone is normally produced during formation of primary bone and may also be seen in high bone turnover states such as osteitis fibrosa cystica, as a result of hyperparathyroidism, and Paget's disease or during high bone formation during early treatment with fluoride.

The periosteum is a fibrous connective tissue sheath that surrounds the outer cortical surface of bone, except at joints where bone is lined by articular cartilage, which contains blood vessels, nerve fibers, and osteoblasts and osteoclasts. The periosteum is tightly attached to the outer cortical surface of bone by thick collagenous fibers, called Sharpeys’ fibers, which extend into underlying bone tissue. The endosteum is a membranous structure covering the inner surface of cortical bone, trabecular bone, and the blood vessel canals (Volkman's canals) present in bone. The endosteum is in contact with the bone marrow space, trabecular bone, and blood vessel canals and contains blood vessels, osteoblasts, and osteoclasts.


Cell Types in Bones

Bone consists of four types of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor cells. Osteoblasts are bone cells that are responsible for bone formation. Osteoblasts synthesize and secrete the organic part and inorganic part of the extracellular matrix of bone tissue, and collagen fibers. Osteoblasts become trapped in these secretions and differentiate into less active osteocytes. Osteoclasts are large bone cells with up to 50 nuclei. They remove bone structure by releasing lysosomal enzymes and acids that dissolve the bony matrix. These minerals, released from bones into the blood, help regulate calcium concentrations in body fluids. Bone may also be resorbed for remodeling, if the applied stresses have changed. Osteocytes are mature bone cells and are the main cells in bony connective tissue these cells cannot divide. Osteocytes maintain normal bone structure by recycling the mineral salts in the bony matrix. Osteoprogenitor cells are squamous stem cells that divide to produce daughter cells that differentiate into osteoblasts. Osteoprogenitor cells are important in the repair of fractures.


What is head of a bone? - Biology

To fully understand movement, artists need to become familiar with the mechanics of the joints. While muscles are important because they are responsible for moving the bones, the joints play a vital role in the movement of the human figure&mdashits limitations as well as its capabilities. This chapter focuses on the various joints and their movements.

Basic Joint Types

The are three basic types of joints&mdashfibrous, cartilaginous, and synovial. Of these, the synovial joints are of the greatest interest to artists, but let’s take a brief look at the other two types before turning our attention to the several different categories of synovial joints.

Fibrous Joints

Fibrous joints are held together with fibrous connective tissue. There are three different types of fibrous joints, shown in the drawing at right: suture joints, gomphosis joints, and syndesmosis joints. Suture joints are fused, immovable joints with a zigzag appearance examples are the suture joints of the cranium. Gomphosis joints (pron., gom-FOH-sis) are immovable joints in which a peglike structure fits into a socket examples are the gomphosis joints of the teeth, each of which is individually rooted in a tooth socket. Syndesmosis joints (pron., SIN-dez-MOH-sis) are capable of slight movement because the fibrous connective tissue (interosseous membrane) that binds the bones together is slightly longer than that of the other two fibrous joints. Syndesmosis joints are found between the ulna and radius bones of the lower arm and the tibia and fibula bones of the lower leg.

FIBROUS JOINTS&mdashTHREE TYPES

Cartilaginous Joints

Cartilaginous joints (pron., KAR-tih-LAAJ-ih-nuss) are connected together with a cartilage-like connective tissue, usually in the form of a fibrocartilaginous disc. There are two different types of cartilaginous joints: synchondrosis joints and symphysis joints. Synchondrosis joints (pron., sin-kon-DROH-sis) are immovable an example is the joint between the first costal cartilage of a rib and the sternum. Symphysis joints (pron., SIM-fih-sis) are slightly movable and are located on the midline (medial line) of the body. Examples are the joints between the vertebrae (intervertebral disc joints), which have small fibrocartilage pads called intervertebral discs, and the joint between the pubic bones, called the pubic symphysis.

CARTILAGINOUS JOINTS&mdashTWO TYPES

Synovial Joints

Also called movable joints, synovial joints (pron., sih-NO-vee-al) are essential for artists to know because of the tremendous variety of movement possibilities they enable. The outer ends of the bones that articulate with each other in synovial joints have a protective coating of articular cartilage to reduce friction and minimize wear and tear during movement. These joints are also encapsulated in an outer layer of fibrous tissue (mainly ligaments) and an inner layer called the synovial membrane. The synovial membrane contains synovial fluid, which functions as a lubricant for the joint. This entire structure is called the joint capsule. Joint capsules are found only at the synovial joints.

Each of the various types of synovial joints&mdashball-and-socket, hinge, pivot, saddle, gliding/plane, and ellipsoid/condyloid&mdashproduces a distinctive kind of movement, as can be seen in the drawings here.

In a ball-and-socket joint, a ball-shaped head on one bone fits into a cuplike socket on another bone.

A ball-and-socket joint is just what the term says: a spherelike structure fitting into a cuplike structure. Examples include the shoulder joint (glenohumeral joint) and hip joint (femoroacetabular joint). Of all the types of synovial joints, ball-and-socket joints have the greatest ability to move bones in many different directions.

In a hinge joint, a convex surface on one bone fits into a concave surface on another bone.

A hinge joint produces more limited movement, in that it can only move a bone in one direction and then return the bone back to its original position, much like the opening and closing of a door (hence the name). Hinge joints include the lower-jaw joint (temporomandibular joint, or TMJ), elbow joint (humeroulnar joint), knee joint (tibiofemoral joint), ankle joint (talocrural joint), and the finger and toe joints (interphalangeal joints). Some anatomists consider the TMJ and knee joint to be modified hinge joints rather than true hinge joints because subtle subsidiary movements, such as rolling and gliding of the bones, occur within these joints.

In a pivot joint, the rounded end of one bone rotates within a ringlike structure formed by another bone or a ligament.

A pivot joint has the ability to swivel a bone on its own axis&mdashas when you shake your head “no” or turn your hand from an upward to a downward position. Joints of this type are found at the upper neck (alanto-axial joint), elbow (proximal radioulnar joint), and wrist (distal radioulnar joint).

In a saddle joint, the two articulating ends of bones are shaped somewhat like saddles, with convex and concave surfaces, and are positioned perpendicularly, one overtop the other.

A saddle joint has slightly more movement than a hinge joint because of its saddlelike concave and convex articulating surfaces. The best-known saddle joint is the carpometacarpal joint at the base of the thumb, which helps move the thumb forward and back as well as across the palm, back to its normal position, and then out to the side. Some anatomists also consider the sternoclavicular (SC) joint between the inner end of the clavicle and the manubrium of the sternum to be a saddle joint.

In a gliding joint, two bones with flat or slightly curved surfaces glide across each other.

A gliding joint, or plane joint, has the least movement capability of all the synovial joints. As the name implies, the bones simply glide against each other. Gliding joints include the carpal joints (intercarpal joints), the tarsal joints (intertarsal joints), the carpal and metacarpal joints (CMC joints), and the pelvis joint (sacroiliac joint) they also occur between the ribs and vertebral column (costovertebral joints), the sternum and ribs (sternocostal joints), and the acromion process and clavicle (acromioclavicular joint).

In an ellipsoid joint, the end of one bone, shaped like an elongated oval, fits into the elongated, oval-shaped cavity of another bone.

An ellipsoid joint, or condyloid joint, is similar to a ball-and-socket joint, but the shapes of the head of one bone and the socket of the other bone are more elongated&mdashoval rather than round. Movements produced by ellipsoid joints are therefore slightly more limited than those enabled by ball-and-socket joints. Ellipsoid joints are located at the connection of the head and neck (atlanto-occipital joint), wrist (radiocarpal joint), and knuckles of the hand (metacarpophalangeal joints).

In addition to the joints described previously, there is what is called a functional joint. For example, the articulation between the scapula bone and the posterior portion of the rib cage is not a true joint because the scapula and rib cage are not held together with connective tissues such as ligaments, nor does it have a joint capsule. However, this articulation does function as a joint, hence the term.

Basic Joint Movements

Muscles contract to move bones at the joints. Movements include forward and backward motions, side-to-side motions, and rotational motions of bones or body parts. Each of these movements has a name identifying the direction of the movement. For every basic action there is a reverse action, so the terms are usually paired. For example, the torso can bend forward at the waist in the movement called flexion, then return to its original upright position in the movement called extension. In addition, most movements can be characterized as angular, rotational, circular, or gliding.

An angular movement changes the angle between two bones (increasing or decreasing the joint angle). Angular movements include flexion and extension as well as abduction and adduction.

In a rotational movement, a bone rotates on its own axis without changing its position spatially. These movements include medial and lateral rotation as well as pronation and supination.

In a circular movement (circumduction), a bone or body part produces a movement in a cone-shaped configuration, with the apex of the imaginary cone located at the joint initiating the action. In other words, one end of the bone (within the joint) is somewhat stationary while the other end of the bone moves in a circular fashion.

In gliding movements, one bone glides over another bone to produce a limited action. These movements include protraction and retraction as well as eversion and inversion.

Note that the overall movement of a joint can also include subsidiary movements in which one bone surface slides over, rolls over, or spins around another. A combination of these three types of motions can be found, to a greater or lesser degree, in all synovial-joint movements.

Anatomical Planes

To help classify the different directions of bodily movements, anatomists have formalized a system of three basic anatomical planes in relation to the body standing in the anatomical position&mdashwhich, again, is the position of a standing figure whose head and palms of the hands are facing forward and whose weight is evenly distributed on both feet. The anatomical planes&mdashcalled the sagittal, coronal, and transverse planes&mdashare used for reference when identifying the various angular and rotational movements of the joints. Think of these imaginary planes as flat, two-dimensional spatial fields or as sheets of transparent glass slicing through the body perpendicularly to each other. Certain movements can take place only within certain planes.

The sagittal plane divides the body vertically into equal right and left halves. Movements within the sagittal plane are flexion and extension&mdashforward and backward movements of the head, spine, and limbs.

The coronal plane divides the body vertically into equal front (anterior) and back (posterior) portions. Movements within the coronal plane are abduction and adduction (side-to-side movements of the arms and legs), as well as lateral flexion (a side-to-side movement of the head, neck, or torso).

A transverse plane divides the body horizontally into upper (superior) and lower (inferior) portions. Movements within a transverse plane include the rotation of the head, spine, or limbs.

Although, as I say above, certain movements are restricted within the boundaries of one of these planes, many complex actions occur in two or three planes: think of a baseball pitcher moving the whole arm in a circular manner to pitch the ball, or a martial arts master executing a powerful kick.

Anterior three-quarter view of a figure in the anatomical position

Sagittal plane
Movements in this plane are forward and backward movements of the head, spine, and limbs.

Coronal plane
Movements in this plane are side-to-side movements of the head, neck, torso, and limbs.

Transverse plane
Movements in this plane are rotations of the head, spine, and limbs.

The Individual Joints of the Skeleton

We will now move through the whole skeleton and examine the main joints of each section of the body. The description of the joint will be followed by the kind or kinds of movement it produces. Locations of the most important joints and the category to which each belongs are identified in the following drawings.

LOCATION OF MAIN JOINTS OF SKELETON&mdashANTERIOR VIEW

LOCATION OF MAIN JOINTS OF SKELETON&mdashPOSTERIOR VIEW

Mandible Joint

All the joints of the cranium, with one exception, are suture (fused) joints, incapable of any movement. These joints are seen on skulls as zigzagging lines on the dome of the cranium and a few of the facial bones. The only moveable joint of the cranium is the temporomandibular joint, or TMJ.

The TMJ is the articulation between the condylar process (a pronglike structure on the lower jaw) and the condylar fossa (a depression) of the temporal bone of the skull. Located directly in front of the ear, the TMJ cannot be seen on the surface, as it is covered with ligaments, muscles, and soft-tissue forms. The TMJ’s appearance is similar to that of an ellipsoid/condyloid joint, but it is classified as a modified hinge joint.

The mandible is capable of three types of movement: depression and elevation (opening and closing of the lower jaw), protraction and retraction (forward and backward movement of the lower jaw), and lateral excursion (the side-to-side movements of the lower jaw, also known as left and right deviation). These jaw movements are utilized mainly for chewing and grinding food, but also in certain vocalizations when the jaw is open.

The next drawing, Depression and Elevation of Mandible at the TMJ (Temporomandibular Joint), shows the hinge-like movement of the jaw. Depression is the lowering of the jaw, opening the mouth wide. Elevation is the movement of returning the jaw back to its normal position. These movements are seen in various facial expressions and in vocalizations in which the jaw is dropped and mouth opened to project the voice when singing or calling out.

DEPRESSION AND ELEVATION OF MANDIBLE AT THE TMJ (TEMPOROMANDIBULAR JOINT)

Modified hinge joint action

Neutral position of mandible

Joints of the Vertebral Column, Rib Cage, and Pelvis

This section covers the cervical joints of the neck, the thoracic vertebral joints of the rib cage, the lumbar joints between the rib cage and pelvis, and the lumbosacral joint of the pelvis, as well as several additional joints of the rib cage and pelvis. We will see how the joints of the cervical (neck) vertebrae move the cranium and how the joints of the thoracic and lumbar region help move the rib cage and pelvis in different directions as whole units.

The Joints of the Vertebral Column

Most of the movement in the vertebral column occurs in the neck region (cervical vertebrae) and the small of the back (lumbar vertebrae), with minor movements occurring in the rib cage (thoracic vertebrae). The range of motion of the vertebral column depends on many factors: An individual’s level of fitness can make a difference in the motion capability of his or her vertebral column. Athletically trained people have more flexibility in their spines than people who are sedentary. Other contributing factors include the flexibility or resistance of the muscles and ligaments of the back and the condition of the various vertebral bones and joints. Age plays a factor, with elderly people tending to lose flexibility of the vertebral column due to bone and disc degeneration.

The joints of the vertebrae, shown in the next drawing, include both cartilaginous and synovial joints. Let’s look at the two basic vertebral joint types: intervertebral joints and vertebral facet joints.

JOINTS OF VERTEBRAL COLUMN&mdashLATERAL VIEW

Intervertebral joints (pron., in-ter-VER-teh-brul), also called disc joints, are cartilaginous joints located between the drumlike shapes of the vertebrae. A fibrocartilaginous pad called the intervertebral disc is positioned between every two vertebrae with the exception of C1 and C2. These discs serve as protective cushions, reducing the friction between bones during joint action, and also act as shock absorbers and weight-bearing structures.

Vertebral facet joints are synovial joints located on the vertebral arches. A facet on one vertebral arch articulates with a facet of the adjacent vertebral arch. These joints are considered gliding, or plane, joints.

The cervical, or neck, vertebrae play an important role not only in supporting the weight of the cranium but in allowing the head to move in different directions. The two primary joints of this region are the atlanto-occipital joint and the atlanto-axial joint.

The atlanto-occipital joint (pron., at-LAN-toe ock-SIP-ih-tal), or AOJ, is the joint between the occipital bone of the cranium and the first cervical vertebra (atlas, or C1). It is classified as an ellipsoid/condyloid joint. The main actions at the AOJ are flexion and extension&mdashrocking the head back and forth, as when nodding “yes.” Other actions include lateral flexion and circumduction of the head and neck.

The atlanto-axial joint (pron., at-LAN-toe AXE-see-al), or AAJ, is the joint between the first cervical vertebra (atlas, or C1) and second cervical vertebra (axis, or C2). The articulation occurs between the odontoid process (or dens), a small bony projection on the axis vertebra, and the inner surface of the atlas vertebra. The atlanto-axial joint, classified as a pivot joint, allows rotational movement of the head and neck, as when the head swivels to the right and left in shaking the head “no.” The drawing below shows the atlanto-occiptal and atlanto-axial joints.

ATLANTO-OCCIPITAL AND ATLANTO-AXIAL JOINTS

Lateral view of cranium and upper cervical vertebrae

Names of Vertebral Joints

The names of vertebral joints provide clues to their location:

·&emspOccipital pertains to the occipital region of the cranium.

·&emspAtlanto pertains to the first cervical (atlas) vertebra.

·&emspAxial pertains to the second cervical (axis) vertebra.

·&emspVertebral pertains to the body of a vertebra.

·&emspTransverse pertains to the transverse processes of a vertebra.

·&emspLumbo pertains to the lumbar vertebrae.

·&emspSacral pertains to the sacrum bone.

Now let’s look at how the whole neck participates in moving the head. Movements of the neck and head include flexion and extension (bending the head and neck forward and back), lateral flexion (bending the head and neck to the side), and rotation (horizontal swiveling of the head and neck). The next drawing, Flexion and Extension of Head and Neck at Cervical Vertebral Joints, shows the head and neck moving in a forward and back direction. Flexion is the action of bending the head forward and downward toward a stationary rib cage, and extension is the return of the head and neck to its normal position. Bending the head back with the chin lifting upward is sometimes called hyperextension&mdashthat is, extending the body part beyond the normal limit.

FLEXION AND EXTENSION OF HEAD AND NECK AT CERVICAL VERTEBRAL JOINTS

Head bends forward with chin pulling in.

Extension of head and neck

Head bends back with chin pulling up.

In the drawing Lateral Flexion of Head and Neck at Cervical Vertebral Joints, we see the head and neck moving sideways. Lateral flexion is the bending of the head toward either the right or left shoulder. This action causes one side of the neck to stretch while the other side contracts.

LATERAL FLEXION OF HEAD AND NECK AT CERVICAL VERTEBRAL JOINTS

Head and neck tilt toward right shoulder. (Head can also tilt toward the left shoulder, in left lateral flexion.)

LEFT: Neutral position of head and neck

RIGHT: Right lateral flexion

Finally, in the drawing Rotation of Head and Neck at Cervical Vertebral Joints, shown next, we see how the head and neck swivel or turn. When the rib cage is stationary, the head and neck can rotate either to the right or to the left. There is, however a limitation in the rotational movement because of the configuration of the cervical vertebrae and the ligaments attaching to them. Ordinarily, the chin cannot move past the shoulder line however, if the head tilts dramatically back and rotates, then the chin can move slightly past the shoulder.

ROTATION OF HEAD AND NECK AT CERVICAL VERTEBRAL JOINTS

Pivot and gliding joint action

The head and neck can also rotate toward the right (right rotation).

LEFT: Neutral position of head and neck, posterior view

RIGHT: Left position of head and neck, posterior view

The Joints of the Rib Cage

The rib cage consists of twelve pairs of ribs that connect to two primary bony structures: the thoracic vertebrae (positioned in the posterior region of the rib cage), and the sternum (positioned in the anterior region of the rib cage). Note that the three pairs of false ribs do not connect directly to the sternum, and that the two pairs of floating ribs at the bottom of the rib cage do not connect to the sternum at all. Let’s look first at the connections between the ribs and the vertebral column, as shown in the drawing Joints of Rib Cage and Vertebral Column.

JOINTS OF RIB CAGE AND VERTEBRAL COLUMN

Throughout the vertebral column we see the numerous intervertebral joints and vertebral facet joints, as discussed above. Additional joints occur as the ribs connect into the vertebral column. These are called the costotransverse joints and the costovertebral joints. A costovertebral joint (pron., CO-sto-VER-teh-brul) connects a rib to the drumlike body of a vertebra this type of joint can be seen in the drawing of the anterior region of the rib cage on this page. A costotransverse (CO-sto-TRANS-verse) joint connects a rib to the transverse process of a vertebra (the horizontal bony protrusion). The term costo means “rib,” and this prefix helps clarify that these particular joints occur only when the ribs attach directly into the thoracic vertebrae.

Names of Rib Cage Joints

The names of rib cage joints provide clues to their locations:

·&emspCosto or costal pertains to the ribs.

·&emspVertebral pertains to the vertebrae.

·&emspSterno pertains to the sternum (breastbone).

·&emspChondral pertains to cartilage.

Now, let’s look at the placement of the joints connecting the ribs to another primary bony structure&mdashthe sternum (breastbone), positioned in the anterior portion of the rib cage. As shown in the next drawing Joints of Rib Cage and Sternum, these joints are the sternocostal joints (located between cartilage and sternum), the costochondral joints (between rib and cartilage), and the interchondral joints (between cartilage sections in the thoracic arch). The sternum itself has two separate joints: the manubriosternal joint and the xiphisternal joint.

The joints between the costal cartilages of the first seven ribs and sternum are called the sternocostal joints (pron., STER-no-CO-stol). The articulation of the first rib and the sternum produces no movement because it is a cartilaginous joint. The joints between the sternum and ribs numbers 2 through 7 are gliding/plane joints that produce minimal gliding movements, usually not noticeable on the surface.

JOINTS OF RIB CAGE AND STERNUM

The costochondral joints (pron., co-sto-CON-drul) are between the ribs and the costal cartilage. Since there are no joint capsules, there is very little motion at these joints.

The interchondral joints (pron., in-ter-CON-drul) are small fibrous connections between the costal cartilage in the thoracic arch region. They are considered gliding/plane joints.

The first of the sternum joints is the manubriosternal joint (pron., maa-NEW-bree-oh-STERN-ul), which is between the manubrium of the sternum and the body of the sternum. It is a symphysis type of cartilaginous joint but often fuses together in middle age or later. The other sternum joint, the xiphisternal joint (pron., ZIF-ih-STERN-ul), is between the xiphoid process and the body of the sternum. It is a synchondrosis type of cartilaginous joint but also fuses together in middle age or later.

Movement is minimal at the rib cage joints, activated mainly during breathing. During inhalation the diaphragm contracts and moves downward to allow the lungs to expand, filling with air the ribs are pulled slightly upward and out, much like levers, to widen the rib cage. In exhalation, the ribs, diaphragm, and lungs return to their normal position. Although these movements are subtle and hard to detect during normal breathing, you can clearly see them when watching the rib cage of an athlete after an exhausting event, such as a sprint.

In the drawing Rib Cage Movement during Respiration, we see the rib cage on the left in the normal state. The middle drawing shows the rib cage immediately after inhalation, when the lungs are filled with air. On the right we see how the rib cage returns back to normal position immediately after exhalation.

RIB CAGE MOVEMENT DURING RESPIRATION

Arrows indicate directional movement within rib cage.

Normal position of rib cage.

Air is expelled from the lungs, and the position of the rib cage returns to normal.

Movements of the Vertebral Column with the Rib Cage

Because the ribs connect into the thoracic vertebrae, restricting movement, the thoracic joints are not as flexible as the cervical or lumbar joints. Whenever there is movement of the vertebral column, the rib cage generally moves as a single unit, in a forward or backward direction (flexion and extension), bending sideways (lateral flexion), or twisting or swiveling (rotation).

In the drawing Flexion and Extension of Rib Cage at the Vertebral Joints, we see how the rib cage moves in a forward and back direction. Flexion is the movement of bending the torso (rib cage and vertebral column) forward from a stationary pelvis. Extension is returning the torso to its normal position or bending the torso back, which is sometimes called hyperextension.

FLEXION AND EXTENSION OF RIB CAGE AT THE VERTEBRAL JOINTS

LEFT: Flexion of torso and vertebral column

CENTER: Neutral position of vertebral column, lateral view

RIGHT: Extension of torso and vertebral column

In the following drawing, Lateral Flexion of the Rib Cage at the Vertebral Joints, we see the torso bending in a side direction, called lateral flexion, from a stationary pelvis. The torso can, of course, bend toward either the right or left.

LATERAL FLEXION OF THE RIB CAGE AT THE VERTEBRAL JOINTS

The vertebral column is in neutral position.

LATERAL FLEXION OF THE RIB CAGE AT THE VERTEBRAL JOINTS (CONTINUED)

The figure leans toward the right from a stationary pelvis. (Movement can also be of the figure leaning toward the left.)

The drawing Rotation of the Rib Cage at the Vertebral Joints, shows how the rib cage can turn on the axis of the vertebral column, rotating the torso (cranium, rib cage, and vertebral column) toward either the right or left (right rotation, left rotation) from a stationary pelvis.

ROTATION OF THE RIB CAGE AT THE VERTEBRAL JOINTS

Pivotal and gliding joint action

The torso, head, and neck are shown rotating toward the right. The torso, neck, and head can also rotate toward the left. Vertebral column in neutral position shown here.

Positions of the spinous processes of the vertebral column

Pivotal movements of the head, neck, and rib cage from the vertebral column

The Joints of the Pelvis

As we move down the vertebral column beyond the rib cage, we encounter the lumbar vertebrae. These large forms help support the weight of the head, neck, and rib cage. The lumbar joints help move the rib cage when the pelvis is more or less stationary, but they also assist in moving the pelvis to various positions.

The joint between the last lumbar vertebra (L5) and the sacrum is called the lumbosacral joint (pron., LUM-bo-SAY-krul). This gliding/plane joint, along with the assistance of the other lumbar joints and the hip joint, allows the pelvis to move in slightly different directions as a whole unit.

Anterior three-quarter view of pelvis

The pelvis contains two other types of joints&mdashthe two sacroiliac joints (pron., SAY-kro-IL-ee-ak located between the sacrum and ilium) and the pubic symphysis joint (pron., PYOO-bic SIM-fih-sis located between the two pubic bones). The sacroiliac and pubic symphysis joints are capable of small, limited gliding motions (interpelvic motions), too subtle to detect on the surface. Artists should think of the pelvis as a single structure that moves as a unit and not as individual bones shifting up or down.

Movements of the whole pelvis as a single unit include anterior and posterior pelvis tilts (tilting forward and backward), lateral flexion (bending of the pelvis to the side), and rotation of the whole pelvis toward either the right or left. The lumbar joints and hip joint (femoroacetabular joint) participate in these movements.

The drawing Anterior and Posterior Pelvic Tilts, shows the pelvis tilting in forward and backward directions. Anterior pelvic tilt (APT) is the tilting of the upper part of the pelvis in a forward and downward direction. The buttocks are lifted upward during this movement, and the vertebral column is usually arched. Posterior pelvic tilt (PPT) is the tilting of the upper part of the pelvis backward. The buttocks are tucked in during this movement.

ANTERIOR AND POSTERIOR PELVIC TILTS

Neutral position of pelvis, lateral view

From a lateral view, the ASIS appears to be positioned somewhat vertically over the pubic bone.

ANTERIOR AND POSTERIOR PELVIC TILTS (CONTINUED)

Anterior pelvic tilt (APT), lateral view

The upper part of the pelvis tilts in a forward and downward direction. Each ASIS is in a lower position than when the pelvis is in neutral position.

ANTERIOR AND POSTERIOR PELVIC TILTS (CONTINUED)

Posterior pelvic tilt (PPT), lateral view

The upper part of the pelvis tilts back. Eash ASIS is in a higher position than when the pelvis is in neutral position.

In the drawing Lateral Flexion of Pelvis at the Lumbosacral Joint, we see the pelvis tilting sideways. Lateral flexion is tilting the whole pelvis sideways, either toward the right (right lateral flexion) or left (left lateral flexion).

LATERAL FLEXION OF PELVIS AT THE LUMBOSACRAL JOINT

Right lateral flexion, posterior view

Pelvis tilts toward the right side.

LATERAL FLEXION OF PELVIS AT THE LUMBOSACRAL JOINT (CONTINUED)

Neutral position of pelvis, posterior view

LATERAL FLEXION OF PELVIS AT THE LUMBOSACRAL JOINT (CONTINUED)

Left lateral flexion, posterior view

Pelvis tilts toward the left side.

The drawing Rotation of Pelvis at the Lumbosacral Joint and Lumbar Vertebrae Joints, shows the action of swiveling the hips as the pelvis rotates toward the right and left.

ROTATION OF PELVIS AT THE LUMBOSACRAL JOINT AND LUMBAR VERTEBRAE JOINTS

Pivotal and gliding joint action

LEFT: Rotation of pelvis toward the right, anterior view

CENTER: Neutral position of pelvis, anterior view

RIGHT: Rotation of pelvis toward left, anterior view

Joints of the Upper Limb and Shoulder Girdle

The main joints of the upper limb are the shoulder joint, elbow joint, wrist joint, and joints of the hand (including finger joints and thumb joints). The drawing shows their locations, identifying the type of each joint.

MAIN JOINTS OF THE UPPER LIMB

Anterior view of right arm in anatomical position

The shoulder girdle, or pectoral girdle, comprises the clavicles (collarbones) and the scapula bones (shoulder blades) and is the supportive framework to which the upper limbs connect. The shoulder girdle has three main joints: the scapulothoracic joint, sternoclavicular joint, and acromioclavicular joint. These joints and the associated bones are shown in the following drawing.

JOINTS OF THE SHOULDER GIRDLE

Rib cage and shoulder girdle, anterior view

The scapulothoracic joint (pron., SKAP-pah-low-thoh-RAS-ik) is the articulation between the scapula bone and the posterior portion of the thorax (rib cage). Anatomically, this is not a true joint, but it is considered a functional joint because of the way the scapula moves in relation to the rib cage.

Names of Shoulder-Girdle Joints

The names of shoulder-girdle joints provide clues to their location:

·&emspScapulo pertains to the scapula bone.

·&emspThoracic pertains to the thorax, or rib cage.

·&emspSterno pertains to the sternum.

·&emspClavicular pertains to the clavicle.

·&emspAcromio pertains to the acromion process of the spine of the scapula.

Movements of the Scapula

It is very beneficial for artists to learn about the scapula bones and how they move. Several muscles attach into these bones, and when the various muscles contract, they move the scapula to slightly different positions on the back. This can noticeably change the topography of the back, with the bulges and valleys of the muscular forms changing from pose to pose. The best way to understand what is occurring on the back is to look for three basic skeletal structures: the rib cage, the vertebral column, and the position of the scapula bones. The presence of the scapula can most easily be detected at the scapula’s medial/vertebral border. You can quickly assess where the scapula bones are by observing the action of the arms, then looking for the medial border, which will enable you to see the approximate location of the scapula bones in that particular pose. From there you can locate the general muscular forms.

In the next drawing, Movements of the Scapula at the Scapulothoracic Joint, we see the many possible positions of the scapula. Since the humerus connects into the scapula, these two bones work as a team in movements of the upper arm. When the humerus moves to different positions, the scapula bone will also move, unless it is intentionally stabilized by certain muscles. The movements of the scapula, shown in the drawing include the following:

·&emspElevation of the scapula: The shoulders lift upward, as in the action of shrugging the shoulders.

·&emspDepression of scapula: The scapula returns to its normal position or slightly lower, which occurs when lifting a heavy weight, such as a barbell.

·&emspAdduction (or protraction) of the scapula: As the upper arm moves back, the scapula moves back toward the vertebral column. This action can be seen in the military stance of attention or when someone is “jabbing” his or her elbows.

·&emspAbduction (or retraction) of the scapula: As the arm reaches forward, the scapula moves away from the vertebral column. This action can be seen when a person crosses both arms in front of the torso or is hunched over. It can also be seen when someone dynamically thrusts the arms forward when reaching for something.

·&emspDownward rotation of the scapula: The scapula tilts, with the bottom tip (inferior angle) moving slightly inward while the acromion process moves downward. The bottom tip of the scapula can also lift slightly away from the rib cage, creating tension in this region. This action can be seen when someone reaches into a back trouser pocket.

·&emspUpward rotation of the scapula: The scapula tilts, with the bottom tip moving slightly outward and the acromion process tilting upward. This action can be seen when the whole arm is lifted upward.

MOVEMENTS OF THE SCAPULA AT THE SCAPULOTHORACIC JOINT

Posterior view of the torso

Left scapula and bones of arms are in normal position

ARROWS: Directional movements of the scapula

RED LINES: Medial/vertebral border of the scapula

The Joints of the Clavicle

Each clavicle (collarbone) attaches to two different bones&mdashthe sternum and the acromion process of the scapula (the outer end of the spine of the scapula)&mdashthus creating two separate clavicular joints: the sternoclavicular joint and the acromioclavicular joint. The clavicle, scapula, and humerus (which attaches into the scapula) are all interconnected, so if one bone moves, the other bones usually move as well.

The sternoclavicular joint (pron., STER-no-cla-VICK-yoo-lar), or SC joint, is the joint between the inner end of the clavicle and the upper portion (manubrium) of the sternum (breastbone). It is usually classified as a gliding/plane joint, but some experts consider it a saddle joint. Movements at the SC joint are elevation and depression of the clavicle and protraction and retraction of the clavicle.

The acromioclavicular joint (pron., ah-CROW-mee-oh-cla-VICK-yoo-lar), or AC joint, is the joint between the outer end of the clavicle and the acromion process of the scapula. It, too, is a gliding/plane joint. Movements at the AC joint are upward and downward rotation of the clavicles and scapula.

To keep things simple, only the clavicles and the sternum are shown in each of the movements depicted in the drawing Movements of Clavicle at the Sternoclavicular (SC) and Acromioclavicular (AC) Joints, below. Remember, however, that when the clavicle moves, the scapula and humerus move, as well. (Note that downward rotation of the clavicle is not shown in the drawing.)

MOVEMENTS OF CLAVICLE AT THE STERNOCLAVICULAR (SC) AND ACROMIOCLAVICULAR (AC) JOINTS

Gliding joint actions, anterior view of the torso

ARROWS: Directional movements of the clavicle

The movements of the clavicle include the following:

·&emspElevation of the clavicle (at the SC joint): The shoulders are shrugged or one shoulder is lifted higher than the other.

·&emspDepression of the clavicle (at the SC joint): The shoulder returns to its normal position from an elevated position, or the outer end of the clavicle drops even lower, as when a person is holding a heavy weight, such as a barbell.

·&emspRetraction of the clavicle (at the SC joint): The shoulders are thrown back, as in the military stance of attention.

·&emspProtraction of the clavicle (at the SC joint): The shoulders roll forward, as when hunching over or folding the arms in front of the torso.

·&emspUpward rotation of the clavicle (at the AC joint): The upper arm (humerus) is lifted up over the head as in the action of abduction, producing an upward rotation of the scapula that results in the outer end of the clavicle lifting upward and slightly rotating (posterior rotation).

(Note that the clavicle appears to be performing the same upward-tilting action in both the elevation of the clavicle and the upward rotation of the clavicle. The difference is that when the clavicle elevates&mdashas when shrugging the shoulders&mdashthe scapula also elevates, with both bones moving in an upward direction, although the inner end of the clavicle at the SC joint remains fixed. In the movement of upward rotation of the clavicle, however, the scapula tilts while the clavicle elevates and rotates.)

The Shoulder Joint

The shoulder joint, known anatomically as the glenohumeral joint (pron., GLEN-o-HYOO-mer-al or GLEE-no-HYOOM-er-al) is the articulation between the head of the humerus (upper arm) and a small, shallow socket on the scapula called the glenoid fossa. This joint, shown in the drawing below, cannot be seen on the surface because it is covered by layers of cartilage, ligaments, and muscles. A ball-and-socket joint, it produces a wide range of movements of the humerus bone, including flexion and extension, abduction and adduction, medial and lateral rotation, and circumduction of the humerus.

SHOULDER (GLENOHUMERAL) JOINT

Posterior lateral view of right scapula and humerus bone

The drawing Flexion and Extension of Humerus at Shoulder Joint, shows the humerus performing a forward-and-back movement. Flexion is the action of moving the humerus in a forward direction and can continue until the whole arm is above the head. Extension is the reverse of this action, in which the humerus is returned to its neutral position at the side of the torso. A continuing movement of the humerus toward the back is sometimes referred as hyperextension of the humerus.

FLEXION AND EXTENSION OF HUMERUS AT SHOULDER JOINT

Ball-and-socket joint action

Lateral view of torso and left arm

MAROON HALF-CIRCLE: Arclike directional movement of the humerus bone as it swings upward or downward

In the drawing Abduction and Adduction of Humerus at Shoulder Joint,, we see the humerus moving sideways away from the torso. Abduction is the action of moving the humerus away from the side of the body and can continue upward until the whole arm is above the head. Adduction is the return of the humerus back to the side of the torso. Adduction of the humerus can continue farther, as when the upper arm is moved across the chest.

ABDUCTION AND ADDUCTION OF HUMERUS AT SHOULDER JOINT

Ball-and-socket joint action

RED LINES: Medial border of the scapula, showing how it changes position as the humerus moves

MAROON HALF-CIRCLE: Arclike directional movement of humerus bone as it swings upward or downward

Next, in the drawing Lateral and Medial Rotation of Humerus at Shoulder Joint, we see the humerus pivoting on its own axis. When the humerus rotates in an outward direction, the action is called lateral rotation because the bone is turning away from the midline of the body. When the humerus rotates in an inward direction, this action is called medial rotation because it is turning toward the midline of the body.

LATERAL AND MEDIAL ROTATION OF HUMERUS AT SHOULDER JOINT

Ball-and-socket joint action

Anterior view of the right upper limb

Finally, in the drawing Circumduction of Humerus at Shoulder Joint, we see the circular movement of the humerus. This movement is often confused with the rotation of the humerus, but the difference is that, in circumduction, the whole humerus (or upper arm) is moving in a circular motion while the head of the humerus at the shoulder joint remains somewhat stabilized. The movement is essentially “drawing a circle” with the hand (with both the upper and lower arm involved) or with the elbow (with the circular movement restricted to the upper arm). Circumduction circles can be broad or narrow and can be executed in a clockwise or counterclockwise direction.

CIRCUMDUCTION OF HUMERUS AT SHOULDER JOINT

Ball-and-socket joint action

Anterior view of right arm and partial torso

The Elbow Joint

The elbow joint actually consists of three joints: the humeroulnar joint, the humeroradial joint, and the proximal radioulnar joint. Although the functions of these three joints are separate, they share the same joint capsule and are grouped together anatomically as a single joint complex.

Posterior three-quarter view of left arm

Names of Elbow-Complex Joints

The names of elbow-complex joints provide clues to their location:

·&emspHumero pertains to the humerus bone.

·&emspRadial or radio pertains to the radius bone.

·&emspUlnar pertains to the ulna bone.

·&emspProximal refers to the area closest to the body part’s point of attachment.

·&emspDistal refers to the area farthest from the body part’s point of attachment.

The humeroulnar joint (pron., HYOO-mer-o-ULL-nar) occurs between the humerus of the upper arm and the ulna of the lower arm. At the base of the humerus is a smooth surface called the trochlea of the humerus, shaped somewhat like a horizontally positioned sewing spool. At the upper part of the ulna, a bony surface called the trochlear notch of the ulna is shaped like a crescent wrench. The crescent-wrench shape of the ulna fits around the spool-like shape of the humerus.

In the drawing Flexion and Extension of Lower Arm at Elbow Joint, we see that the articulation between the humerus and ulna is a hinge joint that produces a back and forth movement of the ulna bone. Flexion is when the lower arm moves toward the upper arm extension is the straightening of the lower arm.

FLEXION AND EXTENSION OF LOWER ARM AT ELBOW JOINT

Lateral view of upper and lower right arm (radius bone of lower arm not shown)

The humeroradial joint (pron., HYOO-mer-oh-RAY-dee-ul) is located between the lower portion of the humerus and the upper portion of the radius bone. At the base of the humerus, positioned next to the trochlea of the humerus, is a spherical form called the capitulum of the humerus. At the upper part of the radius is a small wheel-shaped structure called the head of the radius (or radial head). The top surface of the radial head is slightly concave, and this is where it articulates with the round capitulum. The humeroradial joint is classified as a pivot joint and passively participates in the rotational movements of supination and pronation of the lower arm. This joint does not participate in the hinge movement of the elbow.

The proximal radioulnar joint (pron., PROCKS-sih-mal RAY-dee-oh-ULL-nar) occurs between the head of the radius and a small indentation on the ulna called the radial notch. A small ligament band (annular ligament) attaches from the ulna and encircles the neck and head of the radius bone, acting like a supportive strap keeping the head of the radius in place as it swivels or rotates. The proximal radioulnar joint is anatomically considered part of the elbow joint since it shares the same joint capsule, but the function of this joint is distinct from that of the elbow joint.

The drawing Supination and Pronation of Lower Arm and Hand at Elbow Joint Region, shows rotational movements occurring at the elbow joint and wrist. The humeroradial and proximal radioulnar joints are both pivot joints, and both participate in the actions of supination and pronation. When the lower arm is in the anatomical position, the two bones (radius and ulna) are parallel. Pronation is the rotational movement of the lower arm in which the radius bone pivots or swivels over the relatively stationary ulna bone. When it does this, the hand flips from facing upward or toward the front to facing downward or toward the back. Supination is the reverse of this action, moving the radius back to a position parallel to the ulna. The pivot movement actually takes place on both ends of the radius and ulna bones&mdashat the proximal radioulnar joint, located in the upper region of the radius and ulna bones (and assisted by the humeroradial joint), as well as at the distal radioulnar joint, which is located at the lower region of the radius and ulna bones. (The distal radioulnar joint shares the joint capsule of the wrist joint and is considered by some experts to be part of the wrist joint.)

SUPINATION AND PRONATION OF LOWER ARM AND HAND AT ELBOW JOINT REGION

LEFT: Supination
Palm faces toward the front (right arm in anatomical position).

RIGHT: Pronation
Palm faces toward the back (right arm in anatomical position, pronating).

The Joints of the Wrist Region

At the wrist region are three main joints or groups of joints: the intercarpal joints, the midcarpal joint, and the radiocarpal joint. Of the three, only the radiocarpal joint is (somewhat) detectable on the surface, because it is the transitional region between the lower arm and the hand. It is the main joint involved in the movements of bending the hand at the wrist in different directions.

Wrist region of right hand, dorsal surface

GREEN LINES: Intercarpal joints (joints between all the carpal bones)

DARK PURPLE LINE: Midcarpal joint (joint between the proximal and distal rows of carpal bones)

DOTTED RED LINE: Radiocarpal joint (between the radius bone and the scaphoid, lunate, and triquetral carpal bones)

LIGHT PURPLE AREA: Proximal row of carpal bones

YELLOW AREA: Distal row of carpal bones

The intercarpal joints, also known as carpal joints, are the joints between the eight carpal bones. The midcarpal joint is the joint between the proximal and distal rows of carpal bones. Gliding and slight rotational movements occur between the carpal bones during the movements of flexion, extension, abduction, and adduction of the hand at the wrist joint.

The radiocarpal joint (pron., RAY-dee-o-KAR-poll), also known as the wrist joint, is between the lower end of the radius bone of the lower arm and three of the carpal bones (scaphoid, lunate, and triquetral) of the wrist. These three carpal bones are positioned side by side in a convex alignment that articulates with the concave surface of the end of the radius bone. Because of the overall shape of the articulating surfaces, the radiocarpal joint is classified as an ellipsoid/condyloid joint and is capable of moving the hand at the wrist in many ways, including flexion and extension, abduction adduction, and circumduction (the circular movement of the hand at the wrist).

Movements of the wrist joint include flexion and extension (moving the hand up and down from the wrist) and radial abduction and ulnar adduction (side-to-side movements of hand at the wrist). (The wrist can also perform a circular action called circumduction, but this is not shown in the drawings.)

In the drawing Flexion and Extension of Hand at the Wrist Joint, below, we see the downward and upward movement of the hand from the wrist. Flexion is the action of bending the palm side of the hand toward the anterior region of the lower arm, no matter what position the lower arm is in. Extension is the reverse of this action, returning the hand to its neutral position. Extension can go farther, bending the dorsal part of the hand toward the posterior side of the lower arm, no matter what position the lower arm is in. This action of bending the back of the hand from the wrist is also known as hyperextension.

FLEXION AND EXTENSION OF HAND AT THE WRIST JOINT

Ellipsoid/condyloid joint actions

Lateral view of right hand

In the drawing Ulnar Adduction and Radial Abduction of Hand at the Wrist Joint, we see the movement of tilting the hand sideways from the wrist. Ulnar adduction (also called ulnar deviation) is the sideways tilting of the hand on the side of the lower arm containing the ulna bone. Radial abduction (radial deviation) is the sideways tilting of the hand on the side of the lower arm containing the radius bone this movement is limited by the radial styloid process (a small projection of bone on the radius), which comes into close contact with the scaphoid carpal bone.

ULNAR ADDUCTION AND RADIAL ABDUCTION OF HAND AT THE WRIST JOINT

Ellipsoid/condyloid joint actions, palmar view of the right hand

Ulnar adduction (ulnar deviation)
Hand tilts sideways over ulna.

ULNAR ADDUCTION AND RADIAL ABDUCTION OF HAND AT THE WRIST JOINT (CONTINUED)

Ellipsoid/condyloid joint actions, palmar view of the right hand

ULNAR ADDUCTION AND RADIAL ABDUCTION OF HAND AT THE WRIST JOINT (CONTINUED)

Ellipsoid/condyloid joint actions, palmar view of the right hand

Radial abduction (radial deviation)
Hand tilts sideways over radius.

The Joints of the Hand

The bones of the hand comprise eight carpal bones at the wrist, five metacarpal bones, and fourteen phalanges (twelve finger bones and two thumb bones). Joints between the bones, shown in the next drawing, include the carpometacarpal joints (CMC joints), metacarpophalangeal joints (MCP joints), and interphalangeal joints (IP joints).

Right hand, dorsal surface

IP JOINT: Interphalangeal joint

DIP JOINT: Distal interphalangeal joint

PIP JOINT: Proximal interphalangeal joint

MCP JOINT: Metacarpophalangeal joint

CMC JOINT: Carpometacarpal joint

The carpometacarpal joints (pron., KAR-poe-met-tah-KAR-poll), or CMC joints, are the joints between the carpal and metacarpal bones. All are classified as gliding/plane joints with the exception of the joint between the metacarpal of the thumb and the trapezium carpal bone, which is a saddle joint. There is very little movement at the CMC joints at the second and third metacarpals. Gliding movement occurs in the fourth and fifth metacarpals.

The CMC joint of the thumb has much greater movement capability than the other CMC joints because of the articulating ends on both the trapezium carpal bone and the metacarpal bone of the thumb. Thumb movements include flexion and extension, which are the bending and straightening of the thumb, and abduction and adduction, which are the moving of the thumb away from the palm in a forward direction and the return of the thumb to the side of the hand. These movements are shown in the drawings Abduction and Adduction of Thumb at the CMC Joint and Flexion and Extension of Thumb at the CMC Joint. Other thumb movements, not shown here, are opposition and reposition, in which the thumb moves across the palm to touch the tips of the fingers and then returns to its neutral position, circumduction, which is the circular movement of the entire thumb.

ABDUCTION AND ADDUCTION OF THUMB AT THE CMC JOINT

Neutral position of thumb

Circle indicates the CMC joint of thumb and the saddle joint.

ABDUCTION AND ADDUCTION OF THUMB AT THE CMC JOINT (CONTINUED)

Lateral view of right hand

FLEXION AND EXTENSION OF THUMB AT THE CMC JOINT

In the action of flexion, the thumb is pulled across the palm. The reversal of this action is extension.

Circle indicates the CMC joint of the thumb and the saddle joint.

LEFT: Palmar view of left hand

RIGHT: Thumb moving from the CMC joint

The metacarpophalangeal joints (pron., MET-ah-KAR-poe-fah-LAN-jee-ul), or MCP joints, are the joints between the metacarpal bones and the phalanges (finger bones and thumb bone) and are classified as ellipsoid/condyloid joints. The heads of the metacarpals (commonly referred to as the knuckles of the hand) appear near the surface when the fingers and thumb bend at the MCP joints. When the fingers or thumb extend or straighten, the knuckles are no longer visible on the surface.

The movements of the fingers at the MCP joints are flexion and extension (bending and straightening of the fingers at the MCP joint), abduction and adduction (the spreading of fingers and the return of the spread fingers to normal position), and circumduction, which is the circular movement of a whole finger (not shown in drawing).

In the drawing Abduction and Adduction of Fingers at the MCP Joints, we see the action of spreading the fingers apart and back. The third finger (middle finger) remains stabilized in the movements of abduction and adduction and is considered the midline of the hand. The second finger moves sideways away from the third finger, and the fourth and fifth fingers move sideways away from the third finger in the other direction.

ABDUCTION AND ADDUCTION OF FINGERS AT THE MCP JOINTS

Ellipsoid/condyloid joint actions

Circles indicate MCP joints.

LEFT: Fingers in straight alignment to the palm&mdashpalmer view of the left hand

RIGHT: Fingers spreading outward from the midline is abduction the reverse of this action is adduction

The movements of the thumb at the MCP joint, not shown here, are flexion and extension. Flexion is the bending together of the two phalanges of the thumb at the MCP joint extension returns the two thumb phalanges back to their normal position. The thumb can also slightly rotate from its CMC joint because this joint is a saddle joint, allowing more movement than the ellipsoid/condyloid joint at the MCP.

The interphalangeal joints (pron., in-ter-fah-LAN-jee-ul), or IP joints, are the joints between the phalanges they are classified as hinge joints. They are also referred to as the knuckles of the fingers. The proximal interphalangeal joint (PIP joint) is located between the proximal phalanx (closer to wrist) and the middle (or intermediate) phalanx. The distal interphalangeal joint (DIP joint) is located between the distal phalanx (farther from wrist) and the middle (or intermediate) phalanx. The only movements the fingers can produce at the IP joints (PIP and DIP) are flexion and extension&mdashthe bending and straightening of the phalanges (finger bones).

In the drawing Flexion and Extension of Finger at the IP Joints, we see a lateral view of the straight index finger and, below it, the movements of flexion and extension. In the movement of flexion the finger bones (phalanges) can either bend slightly or tightly curl the whole finger. Extension is the action of straightening the bones of the fingers from a flexed position. As mentioned, flexion and extension also occur at the knuckles (MCP joints) of the hand. The thumb (not shown) has only one IP joint, which also flexes and extends.

FLEXION AND EXTENSION OF FINGER AT THE IP JOINTS

Lateral view of index finger of right hand

Joints of the Lower Limb

The main joints of the lower limb, shown in the drawing next, include the hip joint, knee joint, ankle joint, and the joints of the foot and toes. The pelvic girdle is considered to be an important component of this region because it is the supportive framework into which the lower limbs connect. Since we have already looked at the joints of the pelvis, we focus here on the joints of the lower limb to see how they function in various movements.

MAIN JOINTS OF THE LOWER LIMB

The Hip Joint

The hip joint, also called the femoroacetabular joint (pron., FEM-er-oh-ah-see-TAB-byoo-lar), consists of the golf ball–shaped head of the femur and the cup-shaped socket (acetabulum) within the pelvis. The femur of the upper leg has the capability of moving in a wide variety of directions because of the shape of this ball-and-socket joint. The hip joint itself is hidden under ligaments and muscular forms and so cannot be seen on the surface however, landmarks such as the greater trochanter of the femur can be detected, helping locate the general placement of the hip joint.

HIP JOINT (FEMOROACETABULAR JOINT)

Anterior view of left side of pelvis and upper portion of femur

Movements produced at the hip joint include flexion and extension (moving the femur in forward-and-back directions), abduction and adduction (moving the femur sideways), lateral and medial rotation of the femur (rotating the femur outward or inward), and circumduction (circular motion of entire femur). In the drawing Flexion and Extension of Femur at the Hip Joint, we see the forward-and-back movements of the femur. In flexion, the upper leg can move forward with the lower leg bent or with the lower leg in the same straight alignment as the upper leg. This action is seen in many dance movements and in sports actions such as kicking a ball. Extension is the return of the femur back to its normal position, or it can extend farther back, which is sometimes referred as hyperextension of the femur.

FLEXION AND EXTENSION OF FEMUR AT THE HIP JOINT

Ball-and-socket joint action

Lateral view of pelvis and left upper and lower leg

The drawing Abduction and Adduction of Femur at the Hip Joint, shows the side-to-side movements of the femur. Abduction is the action of moving the femur away from the medial line (midline) of the body. Adduction is the action of returning the femur back to its normal position. Adduction can go farther, moving the femur past the medial line, as in the action of crossing one leg past the other seen in many dance and sports movements.

ABDUCTION AND ADDUCTION OF FEMUR AT THE HIP JOINT

Ball-and-socket joint action

Posterior view of the pelvis and upper and lower legs

Next, in the drawing Lateral and Medial Rotation of Femur at the Hip Joint, we see the rotation of the whole femur, which means the bone is rotating or twisting on its own axis. Medial rotation is rotating the femur toward the midline of the torso lateral rotation is rotating the femur away from the midline. Both medial and lateral rotation can be combined with other movements.

LATERAL AND MEDIAL ROTATION OF FEMUR AT THE HIP JOINT

Ball-and-socket joint action

Anterior view of the pelvis and upper and lower legs
Medial and lateral rotation of left leg with a stationary pelvis

Finally, the drawing Circumduction of Femur at the Hip Joint, shows the circular action of the femur. Circumduction is often confused with the rotation of the femur. The difference is that, in circumduction, the whole femur (or thigh) is moving in a circular manner while the head of the femur remains somewhat stabilized in the hip joint, while in rotation the femur is turning on its own axis. The movement of circumduction is essentially that of drawing an imaginary circle with the foot or knee. It can be performed in either a clockwise or counterclockwise direction, and the circular motion can be broader or narrower.

CIRCUMDUCTION OF FEMUR AT THE HIP JOINT

Ball-and-socket joint action

Anterior view of the pelvis and upper and lower legs

The knee, which is the largest synovial joint in the body, actually consists of two different joints: the tibiofemoral joint, located between the condyles of the femur bone and the condyles of the tibia, and the patellofemoral joint, which is the joint between the lower anterior portion of the femur bone and the patella. The bones of the knee joint are encased in and connected together by strong cartilages and ligaments.

Names of Knee Joints

The names of knee joints provide clues to their location:

·&emspTibio pertains to the tibia bone of the lower leg.

·&emspFemoral pertains to the femur bone of the upper leg.

·&emspPatello pertains to the patella (kneecap).

The tibiofemoral joint (pron., TIB-ee-o-FEM-or-al) consists of the condyles of the femur and the condyles of the tibia. In the drawing Movement of the Tibia or Femur at the Tibiofemoral Joint of the Knee, we see the knee movements of flexion and extension, in which the femur condyles roll and glide on top of the tibia condyles. These actions occur when bending and straightening the lower leg, as when kicking a ball, or when bending and straightening the upper leg over a fixed lower leg, as in the actions of sitting down and standing up. In the action of sitting, the hip joint is also activated. During flexion and extension, there is also a slight lateral rotation or medial rotation of the femur condyles because of these additional minimal movements, the tibiofemoral joint is considered a modified hinge joint.

MOVEMENT OF THE TIBIA OR FEMUR AT THE TIBIOFEMORAL JOINT OF THE KNEE

Modified hinge joint action between the condyles of the femur and tibia

Lateral view of the pelvis and left leg

CENTER: Sitting down and standing up

RIGHT: Lifting and lowering lower leg

The second articulation of the knee joint is the patellofemoral joint (pron., puh-TELL-o-FEM-or-al). This joint between the femur and the patella is considered a gliding/plane joint. The quadriceps tendon runs along a smooth, slightly indented surface on the femur called the patellar surface of the femur, which is located between the two anterior femoral condyles. The tendon attaches into the patella, embedding it in its fibers. The patellar ligament, a straplike form, continues from the lower portion of the patella to attach on the tibial tuberosity, which is a noticeable small protrusion on the upper part of the tibia. The quadriceps tendon, patella, and the patellar ligament act like a cable moving between the large condyles of the femur, which are shaped somewhat like a pulley.

The drawing Movement of the Patella at the Patellofemoral Joint of the Knee, shows how the patella (kneecap) moves during flexion and extension of the knee region. The kneecap moves in slightly upward and downward directions during flexion and extension. Various ligaments attach into the patella to keep it from moving side to side. When the quadriceps muscle contracts on a standing leg, the patella is pulled upward from its normal position.

MOVEMENT OF THE PATELLA AT THE PATELLOFEMORAL JOINT OF THE KNEE

Gliding joint action between the patella and femoral condyles

Lateral view of left knee joint

CENTER: Upper leg bending with fixed lower leg

RIGHT: Lower leg bending with fixed upper leg

When knee is bent (as shown in CENTER and RIGHT images), the patella glides on the patellar surface of the femur, moving slightly downward.

The Ankle Joint

The ankle joint, also called the talocrural joint (pron., TAY-lo-KROO-rul) joins three bones: the lower portions of both the tibia and the fibula bones and the upper portion of the talus bone of the foot. These bones help support the weight of the body and also play an important role in locomotion. The ankle joint is classified as a hinge joint.

As shown in the drawing, the upper portion of the talus (the trochlear portion or talar dome) is smooth and somewhat dome-shaped and is wedged between, or gripped by, the two ankle bones&mdashthe lateral malleolus of the fibula (outer ankle) and medial malleolus of the tibia (inner ankle).

ANKLE JOINT (TALOCRURAL JOINT)

Three-quarter anterior view of the left foot and ankle region

In the drawing Dorsiflexion and Plantar Flexion at the Ankle Joint, we see how the foot moves in up and down directions at the ankle joint. Dorsiflexion is lifting or swinging the front part of the foot upward and pushing the heel downward. In this particular movement, the toes tend to spread apart slightly. This movement occurs in walking and running, preventing the toes from scraping the ground when the foot moves forward in a stride. Plantar flexion is the pointing of the front portion of the foot downward and lifting the heel upward. In this action, the toes tend to push together, as can be seen in many ballet movements. This hingelike action propels the body forward in movements such as walking, running, and leaping.

DORSIFLEXION AND PLANTAR FLEXION AT THE ANKLE JOINT

Non-weight-bearing positions (foot suspended above ground)

DORSIFLEXION AND PLANTAR FLEXION AT THE ANKLE JOINT (CONTINUED)

Weight-bearing positions (foot placed on the ground)

LEFT: Lower leg leans forward, with arch pressed lower to the ground

CENTER: The foot is in neutral position, with normal arch

RIGHT: Lower leg leans back, with arch raised higher

The Joints of the Foot

As Leonardo da Vinci noted, the human foot is a masterpiece of engineering. It is not only capable of supporting the weight of the entire body but also serves as a biomechanical structure helping propel the body in various movements, both horizontally (walking, running) and vertically (jumping).

The bones of the foot comprise seven tarsal bones, five metatarsal bones, and fourteen phalanges (toe bones). The joints of the foot, shown in the drawing on this page, are organized into several groups. The first consists of the joints of the tarsal bones: the subtalar joint, tranverse tarsal joint, tarsometatarsal joints (TMT joints), and various small intertarsal joints. Then there are the joints between the metatarsals and toe bones (the metatarsophalangeal joints, or MTP joints) and the joints of the toes (the interphalangeal joints, or IP joints). Most of the joints between the tarsal bones are considered gliding joints.

Superior view of left foot

Intertarsal joints is the collective name for the many joints between the tarsal bones of the foot. Most important are the subtalar joint, tranverse tarsal joints, and tarsometatarsal joints, but there are also numerous little joints between the three cuneiform tarsal bones and the cuboid and navicular tarsal bones. Each of these smaller joints has its own name, but they are identified in the drawings simply as intertarsal joints.

The subtalar joint (pron., SUB-TAL-ar) is the primary tarsal joint of the foot. This is the joint between the lower portion of the talus bone and the upper portion of the calcaneus bone. It is classified as a gliding joint.

The transverse tarsal joint (pron., TAR-sal) is a combination of two joints: One joint is between the talus and navicular tarsal bones and is classified by some experts as a modified ball-and-socket joint because of its convex and concave surfaces. Its movements, however, are limited. The other is between the calcaneus and cuboid tarsal bones and is considered a gliding joint. This combination of joints travels across the foot, hence the term transverse.

The tarsometatarsal joints (pron., TAR-so-MET-a-tar-sal) are the joints between the tarsal bones (cuneiform #1–3 and cuboid) and the proximal ends of the metatarsal bones. They are gliding joints. In weight-bearing movements such as walking, running, and jumping, these joints can alter the general shape of the arches by flattening the foot or “cupping” the foot, depending on the action.

Names of Foot Joints

The names of foot joints provide clues to their location:

·&emspTarso pertains to the tarsal bones.

·&emspTalo or talar pertains to the talus (a tarsal bone).

·&emspMetatarso pertains to the metatarsal bones.

·&emspPhalangeal pertains to the phalanges (toe bones).

·&emspCalcaneo pertains to the calcaneus (heel bone).

·&emspTransverse means “lying across the long axis of a body part” (in this case, the foot).

·&emspSub means “beneath” (a prefix to other terms).

The movements of eversion and inversion of the foot are produced by gliding and sliding movements between the tarsal and metatarsal bones, combined with movements of dorsiflexion and plantar flexion. These subtle movements are necessary to keep the body balanced when walking on unstable ground, such as a rocky path or sandy terrain. They are also implemented in sports actions such as cupping the foot when hitting a soccer ball or turning the flattened foot outward in martial-arts kicking maneuvers. In the drawing Eversion and Inversion of Foot at the Tarsal and Metatarsal Joints, we see how the foot can bend slightly outward or inward. Eversion is turning the sole or bottom of the foot outward, away from the midline of the body, as when hitting a hacky sack with the outer edge of the foot. Inversion is turning the sole or bottom of the foot toward the midline of the body, as when you look at the bottom of your foot with the sole curling toward you. Inversion can also often be seen in soccer, when a player lifts the ball with the inner edge of the foot.

EVERSION AND INVERSION OF FOOT AT THE TARSAL AND METATARSAL JOINTS

LEFT: Inversion of left foot

RIGHT: Eversion of left foot

The two main types of toe joints are the metatarsophalangeal joints (MTP joints) and the interphalangeal joints (IP joints). The movements of the toes, while not as dynamic as those of the fingers, are nonetheless important in the gait mechanics of walking, running, and other actions. When, in walking, the foot moves off the ground and swings in a forward direction, the toes extend upward and spread slightly to avoid being dragged against the ground. As the foot lands, the toes flex or bend and then “grip” the ground as a stabilizing maneuver.

The metatarsophalangeal joints (pron., MET-a-TAR-so-fa-lan-GEE-al), or MTP joints, are the joints between the heads of the metatarsals and the bases of the phalanges (toe bones). They are considered ellipsoid/condyloid joints.

The interphalangeal joints of the foot (pron., IN-ter-fa-lan-GEE-al), or IP joints, are the joints between the toe bones (phalanges) and are considered hinge joints.

Movements at these joints include abduction and adduction (spreading the toes away from the midline of the foot and then bringing them back together) and flexion and extension (bending and straightening the toes). These actions are shown in the drawings Abduction and Adduction of Toes at the MTP Joint and Flexion and Extension of Toes at the MTP and IP Joints.

ABDUCTION AND ADDUCTION OF TOES AT THE MTP JOINT

Ellipsoid/condyloid joint action

Superior view of left foot

Circles indicate the MTP joints and the ellipsoid/condyloid joints

LEFT: Neutral position of toes

RIGHT: Toes moving at the MTP joint
Abduction is the movement of the great toe and the third, fourth, and fifth toes away from the second toe (midline). Adduction is the reverse of this action.


What is a headache?

Narrowly defined, headache is pain in the head or face, and sometimes also includes pain in the upper neck. Pain sensitive structures in the head and face include the skin, bone and structures in the eyes, ears, nose and mouth. Also, the large blood vessels of the head are exquisitely sensitive and these are the principal organs causing pain in vascular headaches, such as migraines. The jaw hinge (called the temporomandibular joint) and the teeth can also generate headache. The brain itself is not pain sensitive and is not a source of head pain.

The most common type of headache is the tension or muscle contraction type, which is frequently caused by spasms in the neck muscles and the muscles of mastication (chewing). This type of headache is usually treated easily by over-the-counter medications. More intense headaches are caused by unknown mechanisms. Most theories of vascular headache involve the relationship between the nerves and the blood vessels, both of which can be sensitive.

In people who are prone to migraine, these headaches can be triggered by a multitude of causes, including diet, stress, lights, strong smells and other environmental conditions (either external or internal). Once the migraine process has started, it usually requires medication to stop the headache. There are many other specific, less common headache diagnoses, such as cluster headaches and neuralgia, or nerve damage headaches.

All of these headaches have specific treatments, both pharmacological and non-pharmacological (for instance, relaxation or biofeedback techniques). Additionally, there are new medications being developed on an almost monthly basis, all of which hold promise for treating these most painful of headaches. Anyone who suffers from headaches and who has given up on medical treatments should return to his or her family physician and inquire about the new prospects for substantial relief.


What is the medical term for toward the head?

superior or cephalic. Directional term meaning toward the head, or above. inferior or caudal. Directional term meaning toward the feet or tail, or below. anterior or ventral.

Also, which body Direction term means toward the head or pertaining to the head? SUPERIOR (CEPHALIC OR CRANIAL) TOWARD THE HEAD OR TOWARD THE UPPER PART OF A STRUCTURE. INFERIOR (CAUDAL)

Also, what is the medical term for top of head?

Human. Crown can mean the top of the head and it can also mean the whole head. In the study of human anatomy the terms "Calvaria, "skullcap", "skull cap", or the "roof of the cranial cavity" are used for the top part of the head.

What is posterior in medical terms?

Posterior comes from the Latin word posterus, meaning "coming after". Posterior is often used as a technical term in biology and medicine to refer to the back side of things, and is the opposite of anterior, which refers to the front side. When used as a noun, posterior simply means "buttocks".



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