Chapter 16: The musculoskeletal system

Question 1

Functions of the bones

Answer 1

The functions of bones include:

• providing the body framework
• giving attachment to muscles and tendons
• allowing movement of the body as a whole and of parts of the body, by forming joints that are moved by muscles
• forming the boundaries of the cranial, thoracic and pelvic cavities, and protecting the organs they contain
• hemopoiesis, the production of blood cells in red bone marrow
• mineral storage, especially calcium phosphate – the mineral reservoir within bone is essential for maintenance of blood calcium levels, which must be tightly controlled.

Question 2

Types of bones

Answer 2

Bones are classified as long, short, irregular, flat, and sesamoid.

Question 3

Long bones

Answer 3

• These consist of a shaft and two extremities. As the name suggests, these bones are longer than they are wide. Most long bones are found in the limbs; examples include the femur, tibia, and fibula.
• These have a diaphysis (shaft) and two epiphyses (extremities). The diaphysis is composed mainly of compact bone with a central medullary canal, containing fatty yellow bone marrow. The epiphyses consist of an outer covering of compact bone with the spongy (cancellous) bone inside. The diaphysis and epiphyses are separated by epiphyseal cartilages, which ossify when growth is complete.
• Long bones are almost completely covered by a vascular membrane, the periosteum, which has two layers. The outer layer is tough and fibrous and protects the bone underneath. The inner layer contains osteoblasts and osteoclasts, the cells responsible for bone production and the breakdown, and is important in the repair and remodeling of the bone. The periosteum covers the whole bone except within joint cavities, allows attachments of tendons, and is continuous with the joint capsule. Hyaline cartilage replaces the periosteum on bone surfaces that form joints. Thickening of a bone occurs by the deposition of new bone tissue under the periosteum.

Question 4

Short, Irregular, flat, and sesamoid bones

Answer 4

•These have no shafts or extremities and are diverse in shape and size. Examples include:
-short bones – carpals (wrist)
-irregular bones – vertebrae and some skull bones
-flat bones – sternum, ribs, and most skull bones
-sesamoid bones – patella (kneecap).
•These have a relatively thin outer layer of compact bone, with the spongy bone inside containing red bone marrow. They are enclosed by the periosteum except for the inner layer of the cranial bones where it is replaced by the dura mater.

Question 5

Blood and nerve supply

Answer 5

One or more nutrient arteries supply the bone shaft; the epiphyses have their own blood supply, although in the mature bone the capillary networks arising from the two are heavily interconnected. The sensory nerve supply usually enters the bone at the same site as the nutrient artery, and branches extensively throughout the bone. Bone injury is, therefore, usually very painful.

Question 6

The microscopic structure of bone

Answer 6

Bone is a strong and durable type of connective tissue. Its major constituent (65%) is a mixture of calcium salts, mainly calcium phosphate. This inorganic matrix gives bone great hardness, but on its own would be brittle and prone to shattering. The remaining third is an organic material, called osteoid, which is composed mainly of collagen. Collagen is very strong and gives bone slight flexibility. The cellular component of bone contributes less than 2% of bone mass.

Question 7

Bone cells

Answer 7

• There are three types of bone cell:

• osteoblast
• osteocyte
• osteoclast

Question 8

Osteoblasts

Answer 8

•These bone-forming cells are responsible for the deposition of both inorganic salts and osteoid in bone tissue. They are therefore present at sites where the bone is growing, repairing, or remodeling, e.g.:
-in the deeper layers of periosteum
-in the centers of ossification of immature bone
-at the ends of the diaphysis adjacent to the epiphyseal cartilages of long bones
-at the site of a fracture.
•As they deposit new bone tissue around themselves, they eventually become trapped in tiny pockets (lacunae) in the growing bone and differentiate into osteocytes.

Question 9

Osteocytes

Answer 9

These are mature bone cells that monitor and maintain bone tissue and are nourished by tissue fluid in the canali­culi that radiate from the central canals.

Question 10

Osteoclasts

Answer 10

These cells break down bone, releasing calcium and phosphate. They are very large cells with up to 50 nuclei, which have formed from the fusion of many monocytes. The continuous remodeling of healthy bone tissue is the result of the balanced activity of the bone’s osteoblast and osteoclast populations. Osteoclasts are found in areas of the bone where there is active growth, repair, or remodeling, e.g:

• under the periosteum, maintaining bone shape during growth and removing excess callus formed during the healing of fractures
• round the walls of the medullary canal during growth and canalize callus during healing.

Question 11

Compact (cortical) bone

Answer 11

Cortical bone is the dense outer surface of bone that forms a protective layer around the internal cavity. This type of bone also known as compact bone makes up nearly 80% of skeletal mass and is imperative to body structure and weight-bearing because of its high resistance to bending and torsion.

Question 12

Spongy (cancellous trabecular) bone

Answer 12

To the naked eye, spongy bone looks like a honeycomb. Microscopic examination reveals a framework formed from trabeculae (meaning ‘little beams’), which consist of a few lamellae and osteocytes interconnected by canaliculi. Osteocytes are nourished by interstitial fluid diffusing into the bone through the tiny canaliculi. The spaces between the trabeculae contain red bone marrow. In addition, spongy bone is lighter than compact bone, reducing the weight of the skeleton.

Question 13

Development of bone tissue

Answer 13

• Also called osteogenesis or ossification, this begins before birth and is not complete until about the 21st year of life. Long, short and irregular bones develop in the fetus from rods of cartilage, cartilage models. Flat bones develop from membrane models and sesamoid bones from tendon models.
• During ossification, osteoblasts secrete osteoid, which gradually replaces the initial model; then this osteoid is progressively calcified, also by osteoblast action. As the bone grows, the osteoblasts become trapped in the matrix of their own making and become osteocytes.
• In mature bone, a fine balance of osteoblast and osteoclast activity maintains normal bone structure. If osteoclast activity exceeds osteoblast activity, the bone becomes weaker. On the other hand, if osteoblast activity outstrips osteoclast activity, the bone becomes stronger and heavier.

Question 14

Development of long bones

Answer 14

• In long bones the focal points from which ossification begins are small areas of osteogenic cells or centers of ossification in the cartilage model. This is accompanied by the development of a bone collar at about 8 weeks of gestation. Later the blood supply develops, and bone tissue replaces cartilage as osteoblasts secrete osteoid in the shaft. The bone lengthens as ossification continues and spreads to the epiphyses. Around birth, secondary centers of ossification develop in the epiphyses, and the medullary canal forms when osteoclasts break down the central bone tissue in the middle of the shaft. During childhood, long bones continue to lengthen because the epiphyseal plate at each end of the bone, which is made of cartilage, continues to produce new cartilage on its diaphyseal surface (the surface facing the shaft of the bone).
• This cartilage is then turned to bone. If cartilage production matches the rate of ossification, the bone continues to lengthen. At puberty, under the influence of sex hormones, the epiphyseal plate growth slows down and is overtaken by bone deposition. Once the whole epiphyseal plate is turned to bone, no further lengthening of the bone is possible.

Question 15

Hormonal regulation of bone growth

Answer 15

Growth hormone and the thyroid hormones, thyroxine, and triiodothyronine are especially important during infancy and childhood, deficient or excessive secretion of these results in abnormal development of the skeleton.

Question 16

Exercise and bone

Answer 16

• Although bone growth lengthways permanently ceases once the epiphyseal plates have ossified, thickening of bone is possible throughout life. This involves the laying down of new osteons at the periphery of the bone through the action of osteoblasts in the inner layer of the periosteum. Weight-bearing exercise stimulates the thickening of bone, strengthening it and making it less liable to fracture. Lack of exercise reverses these changes, leading to lighter, weaker bones.
• Testosterone and estrogens influence the physical changes that occur at puberty and help maintain bone structure throughout life. Rising levels of these hormones are responsible for the growth spurt of puberty, but later stimulate closure of the epiphyseal plates, so that bone growth lengthways stops (although bones can grow in thickness throughout life). Average adult male height is usually greater than female because male puberty tends to occur at a later age than female puberty, giving a male child’s bones longer to keep growing.
• Calcitonin and parathyroid hormone control blood levels of calcium by regulating its uptake into and release from bone. Calcitonin increases calcium uptake into bone (reducing blood calcium), and parathormone decreases it (increasing blood calcium).

Question 17

Diet and bone

Answer 17

Healthy bone tissue requires adequate dietary calcium and vitamins A, C, and D. Calcium, and smaller amounts of other minerals such as phosphate, iron, and manganese, are essential for adequate mineralization of bone. Vitamin A is needed for osteoblast activity. Vitamin C is used in collagen synthesis, and vitamin D is required for calcium and phosphate absorption from the intestinal tract.

Question 18

Bone markings

Answer 18

Most bones have rough surfaces, raised protuberances, and ridges that give attachment to muscle tendons and ligaments. These are not included in the following descriptions of individual bones unless they are of note, but many are marked on illustrations.

Question 19

Healing of bone

Answer 19

•There are several terms used to classify bone fractures, including:
-simple: the bone ends do not protrude through the skin
-compound: the bone ends protrude through the skin
-pathological: fracture of a bone weakened by disease.
•1: A hematoma (collection of clotted blood) forms between the ends of the bone and in surrounding soft tissues.
•2: There follows the development of acute inflammation and accumulation of inflammatory exudate, containing macrophages that phagocytose the hematoma and small dead fragments of bone (this takes about 5 days). Fibroblasts migrate to the site; granulation tissue and new capillaries develop.
•3: New bone forms as large numbers of osteoblasts secrete spongy bone, which unites the broken ends, and is protected by an outer layer of bone and cartilage; the new deposits of bone and cartilage is called a callus. Over the next few weeks, the callus matures, and the cartilage is gradually replaced with new bone.
•4: Reshaping of the bone continues and gradually the medullary canal is reopened through the callus (in weeks or months). In time the bone heals completely with the callus tissue completely replaced with mature compact bone. Often the bone is thicker and stronger at the repair site than originally, and a second fracture is more likely to occur at a different site.

Question 20

Tissue fragments between cone ends

Answer 20

Splinters of dead bone (sequestrate) and soft tissue fragments not removed by phagocytosis delay healing.

Question 21

Deficient blood supply

Answer 21

This delays growth of granulation tissue and new blood vessels. Hypoxia also reduces the number of osteoblasts and increases the number of chondrocytes that develop from their common parent cells. This may lead to the cartilaginous union of the fracture, which results in a weaker repair. The most vulnerable sites, because of their normally poor blood supply, are the neck of the femur, the scaphoid, and the shaft of the tibia.

Question 22

Poor alignment of bone ends

Answer 22

This may result in the formation of a large and irregular callus that heals slowly and often results in permanent disability.

Question 23

Continued mobility f bone ends

Answer 23

Continuous movement results in fibrosis of the granulation tissue followed by the fibrous union of the fracture.

Question 24

Miscellaneous

Answer 24

These include infection, systemic illness, malnutrition, drugs, e.g., corticosteroids and aging.

Question 25

Infections

Answer 25

Pathogens enter through broken skin, although they may occasionally be blood-borne. Healing will not occur until the infection resolves.

Question 26

Fat embolism

Answer 26

Emboli consisting of fat from the bone marrow in the medullary canal may enter the circulation through torn veins. They are most likely to lodge in the lungs and block blood flow through the pulmonary capillaries.

Question 27

axial skeleton

Answer 27

* The bones of the skeleton are divided into two groups: the axial skeleton and the appendicular skeleton. * The axial skeleton consists of the skull, vertebral column, ribs, and sternum. Together the bones forming these structures constitute the central bony core of the body, the axis. The appendicular skeleton consists of the shoulder and pelvic girdles and the limb bones.

Question 28

Skull

Answer 28

The skull rests on the upper end of the vertebral column and its bony structure is divided into two parts: the cranium and the face.

Question 29

Sinuses

Answer 29

Sinuses containing air are present in the sphenoid, ethmoid, maxillary, and frontal bones. They all communicate with the nasal cavity and are lined with ciliated mucous membrane. They give resonance to the voice and reduce the weight of the skull, making it easier to carry.

Question 30

Cranium

Answer 30

•The cranium is formed by several flat and irregular bones that protect the brain. It has a base upon which the brain rests and a vault that surrounds and covers it. The periosteum lining the inner surface of the skull bones forms the outer layer of the dura mater. In the mature skull, the joints (sutures) between the bones are immovable. The bones have numerous perfo­rations (e.g., foramina, fissures) through which nerves, blood, and lymph vessels pass. The bones of the cra­nium are: - 1 frontal bone - 2 parietal bones - 2 temporal bones - 1 occipital bone - 1 sphenoid bone - 1 ethmoid bone

Question 31

Frontal bone

Answer 31

* This is the bone of the forehead. It forms part of the orbital cavities (eye sockets) and the prominent ridges above the eyes, the supraorbital margins. Just above the supraorbital margins, within the bone, are two air-filled cavities or sinuses lined with ciliated mucous membrane, which open into the nasal cavity. * The coronal suture joins the frontal and parietal bones and other sutures are formed with the sphenoid, zygomatic, lacrimal, nasal, and ethmoid bones. The frontal bone originates in two parts joined in the midline by the frontal suture

Question 32

Parietal bones

Answer 32

•These bones form the sides and roof of the skull. They articulate with each other at the sagittal suture, with the frontal bone at the coronal suture, with the occipital bone at the lambdoidal suture, and with the temporal bones at the squamous sutures. The inner surface is concave and is grooved to accommodate the brain and blood vessels.

Question 33

Temporal bones

Answer 33

* These bones lie one on each side of the head and form sutures with the parietal, occipital, sphenoid, and zygomatic bones. The squamous part is the thin fan-shaped area that articulates with the parietal bone. The zygomatic process articulates with the zygomatic bone to form the zygomatic arch (cheekbone). * The mastoid part contains the mastoid process, a thickened region easily felt behind the ear. It contains many very small air sinuses that communicate with the middle ear and are lined with squamous epithelium. * The petrous portion forms part of the base of the skull and contains the organs of hearing (the spiral organ) and balance. * The temporal bone articulates with the mandible at the temporomandibular joint, the only movable joint of the skull. Immediately behind this articulating surface is the external acoustic meatus (auditory canal), which passes inwards towards the petrous portion of the bone. * The styloid process projects from the lower process of the temporal bone and supports the hyoid bone and muscles associated with the tongue and pharynx.

Question 34

Occipital bone

Answer 34

This bone forms the back of the head and part of the base of the skull. It forms sutures with the parietal, temporal, and sphenoid bones. Its inner surface is deeply concave, and the concavity is occupied by the occipital lobes of the cerebrum and by the cerebellum. The occiput has two articular condyles that form condyloid joints with the first bone of the vertebral column, the atlas. This joint permits nodding movements of the head. Between the condyles is the foramen magnum (meaning ‘large hole’) through which the spinal cord passes into the cranial cavity.

Question 35

Sphenoid bone

Answer 35

This bone occupies the middle portion of the base of the skull, and it articulates with the occipital, temporal, parietal, and frontal bones. It links the cranial and facial bones and cross-braces the skull. On the superior surface in the middle of the bone is a little saddle-shaped depression, the hypophyseal fossa (Sella turcica) in which the pituitary gland rests. The body of the bone contains some large air sinuses lined with ciliated mucous membrane with openings into the nasal cavity. The optic nerves pass through the optic foramina on their way to the brain.

Question 36

Ethmoid bone

Answer 36

The ethmoid bone occupies the anterior part of the base of the skull and helps to form the orbital cavity, the nasal septum, and the lateral walls of the nasal cavity. On each side are two projections into the nasal cavity, the superior and middle conchae or turbinated processes. It is a very delicate bone containing many air sinuses lined with ciliated epithelium and with openings into the nasal cavity. The horizontal flattened part, the cribriform plate, forms the roof of the nasal cavity and has numerous small foramina through which nerve fibers of the olfactory nerve (sense of smell) pass upwards from the nasal cavity to the brain.

Question 37

Face

Answer 37

``` The skeleton of the face is formed by 13 bones in addition to the frontal bone already described. -2 zygomatic (cheek) bones -1 maxilla -2 nasal bones -2 lacrimal bones -1 vomer -2 palatine bones -2 inferior conchae 1 mandible ```

Question 38

Zygomatic (cheek) bone

Answer 38

The zygomatic bone originates as two bones that fuse before birth. They form the prominences of the cheeks and part of the floor and lateral walls of the orbital cavities.

Question 39

Maxilla (upper jawbone)

Answer 39

This originates as two bones that fuse before birth. The maxilla forms the upper jaw, the anterior part of the roof of the mouth, the lateral walls of the nasal cavity, and part of the floor of the orbital cavities. The alveolar ridge, or process, projects downwards and carries the upper teeth. On each side is a large air sinus, the maxillary sinus, lined with a ciliated mucous membrane and with openings into the nasal cavity.

Question 40

Nasal bone

Answer 40

These are two small flat bones that form the greater part of the lateral and superior surfaces of the bridge of the nose.

Question 41

Lacrimal bones

Answer 41

These two small bones are posterior and lateral to the nasal bones and form part of the medial walls of the orbital cavities. Each is pierced by a foramen for the passage of the nasolacrimal duct that carries the tears from the medial canthus of the eye to the nasal cavity.

Question 42

Vomer

Answer 42

The vomer is a thin flat bone that extends upwards from the middle of the hard palate to form most of the inferior part of the nasal septum. Superiorly it articulates with the perpendicular plate of the ethmoid bone.

Question 43

Palatine bones

Answer 43

These are two small L-shaped bones. The horizontal parts unite to form the posterior part of the hard palate and the perpendicular parts project upwards to form part of the lateral walls of the nasal cavity. At their upper extremities, they form part of the orbital cavities.

Question 44

Inferior conchae

Answer 44

Each concha is a scroll-shaped bone, which forms part of the lateral wall of the nasal cavity and projects into it below the middle concha. The superior and middle conchae are parts of the ethmoid bone. The conchae collectively increase the surface area in the nasal cavity, allowing inspired air to be warmed and humidified more effectively.

Question 45

Mandible (lower jawbone)

Answer 45

This is the lower jaw, the only movable bone of the skull. It originates as two parts that unite at the midline. Each half consists of two main parts: a curved body with the alveolar ridge containing the lower teeth and a ramus, which projects upwards almost at right angles to the posterior end of the body. •At the upper end, the ramus divides into the condylar process which articulates with the temporal bone to form the temporomandibular joint, and the coronoid process, which gives attachment to muscles and ligaments that close the jaw. The point where the ramus joins the body is the angle of the jaw.

Question 46

hyoid bone

Answer 46

This is an isolated horseshoe-shaped bone lying in the soft tissues of the neck just above the larynx and below the mandible. It does not articulate with any other bone but is attached to the styloid process of the temporal bone by ligaments. It supports the larynx and gives attachment to the base of the tongue.

Question 47

Fontanelles of the skull

Answer 47

At birth, ossification of the cranial sutures is incomplete. The skull bones do not fuse earlier to allow for molding of the baby's head during childbirth. Where three or more bones meet there are distinct membranous areas or fontanelles. The two largest are the anterior fontanelle, not fully ossified until the child is between 12 and 18 months old, and the posterior fontanelle, usually ossified 2–3 months after birth.

Question 48

Functions of the skull

Answer 48

The various parts of the skull have specific and different functions: - the cranium protects the brain - the bony eye sockets protect the eyes and give attachment to the muscles that move them - the temporal bone protects the delicate structures of the inner ear - the sinuses in some face and skull bones give resonance to the voice - the bones of the face form the walls of the posterior part of the nasal cavities and form the upper part of the air passages - the maxilla and the mandible provide alveolar ridges in which the teeth are embedded - the mandible, controlled by muscles of the lower face, allows chewing.

Question 49

Vertebral column

Answer 49

* There are 26 bones in the vertebral column. Twenty-four separate vertebrae extend downwards from the occipital bone of the skull; then there is the sacrum, formed from five fused vertebrae, and lastly, the coccyx, or tail, which is formed from between three and five small, fused vertebrae. The vertebral column is divided into different regions. The first seven vertebrae, in the neck, form the cervical spine; the next 12 vertebrae are the thoracic spine, and the next five are the lumbar spine, the lowest vertebra of which articulates with the sacrum. Each vertebra is identified by the first letter of its region in the spine, followed by a number indicating its position. For example, the topmost vertebra is C1, and the third lumbar vertebra is L3. * The movable vertebrae have many characteristics in common, but some groups have distinguishing features

Question 50

The body

Answer 50

This is the broad, flattened, largest part of the vertebra. When the vertebrae are stacked together in the vertebral column, it is the flattened surfaces of the body of each vertebra that articulate with the corresponding surfaces of adjacent vertebrae. However, there is no direct bone-to-bone contact since between each pair of bones is a tough pad of fibrocartilage called the intervertebral disc. The bodies of the vertebrae lie to the front of the vertebral column, increasing greatly in size towards the base of the spine, as the lower spine must support much more weight than the upper regions.

Question 51

The vertebral (neural) arch

Answer 51

This encloses a large vertebral foramen. It lies behind the body and forms the posterior and lateral walls of the vertebral foramen. The lateral walls are formed from plates of bone called pedicles, and the posterior walls are formed from laminae. Projecting from the regions where the pedicle meets the lamina is a lateral prominence, the transverse process, and where the two laminae meet at the back is a process called the spinous process. These bony prominences can be felt through the skin along the length of the spine. The vertebral arch has four articular surfaces: two articulate with the vertebra above and two with the one below. The vertebral foramina form the vertebral (neural) canal that contains the spinal cord.

Question 52

Cervical vertebrae

Answer 52

* These are the smallest vertebrae. The transverse processes have a foramen through which a vertebral artery passes upwards to the brain. The first two cervical vertebrae, the atlas, and the axis are atypical. * The first cervical vertebra (C1), the atlas, is the bone on which the skull rests. Below the atlas is the axis, the second cervical vertebra (C2). * The atlas is essentially a ring of bone, with no distinct body or spinous process, although it has two short transverse processes. It possesses two flattened facets that articulate with the occipital bone; these are condyloid joints, and they permit nodding of the head. * The axis sits below the atlas and has a small body with a small superior projection called the odontoid process (also called the dens, meaning tooth). This occupies part of the posterior foramen of the atlas above and is held securely within it by the transverse ligament. The head pivots (i.e., turns from side to side) on this joint. * The 7th cervical vertebra, C7, is also known as the vertebra prominins. It possesses a long spinous prominence terminating in a swollen tubercle, which is easily felt at the base of the neck.

Question 53

Thoracic vertebrae

Answer 53

The 12 thoracic vertebrae are larger than the cervical vertebrae because this section of the vertebral column must support more bodyweight. The bodies and transverse processes have facets for articulation with the ribs.

Question 54

Lumbar vertebrae

Answer 54

These are the largest of the vertebrae because they must support the weight of the upper body. They have substantial spinous processes for attachment of the muscles of the lower back.

Question 55

Sacrum

Answer 55

This consists of five rudimentary vertebrae fused to form a triangular or wedge-shaped bone with a concave anterior surface. The upper part, or base, articulates with the 5th lumbar vertebra. On each side, it articulates with the ilium to form a sacroiliac joint, and at its inferior tip, it articulates with the coccyx. The anterior edge of the base, the promontory, protrudes into the pelvic cavity. The vertebral foramina are present, and on each side of the bone, there is a series of foramina for the passage of nerves.

Question 56

Coccyx

Answer 56

This consists of the four-terminal vertebrae fused to form a very small triangular bone, the broad base of which articulates with the tip of the sacrum.

Question 57

Intervertebral discs

Answer 57

The bodies of adjacent vertebrae are separated by intervertebral discs, consisting of an outer rim of fibrocartilage (annulus fibrosus) and a central core of soft gelatinous material (nucleus pulposus). They are thinnest in the cervical region and become progressively thicker towards the lumbar region, as spinal loading increases. The posterior longitudinal ligament in the vertebral canal helps to keep them in place. They have a shock-absorbing function and the cartilaginous joints they form contribute to the flexibility of the vertebral column.

Question 58

Intervertebral discs

Answer 58

* When two adjacent vertebrae are viewed from the side, a foramen formed by a gap between adjacent vertebral pedicles can be seen. * Throughout the length of the column there is an intervertebral foramen on each side between every pair of vertebrae, through which the spinal nerves, blood vessels, and lymph vessels pass

Question 59

Intervertebral foramina

Answer 59

* When two adjacent vertebrae are viewed from the side, a foramen formed by a gap between adjacent vertebral pedicles can be seen. * Throughout the length of the column there is an intervertebral foramen on each side between every pair of vertebrae, through which the spinal nerves, blood vessels, and lymph vessels pass

Question 60

Ligaments of the vertebral column

Answer 60

* These ligaments hold the vertebrae together and keep the intervertebral discs in position. * The transverse ligament holds the odontoid process of the axis in the correct position in relation to the atlas. * The anterior longitudinal ligament extends the whole length of the column and lies in front of the vertebral bodies. * The posterior longitudinal ligament lies inside the vertebral canal and extends the whole length of the vertebral * Column in close contact with the posterior surface of the bodies of the bones. * The ligament Flava connects the laminae of adjacent vertebrae. * The ligament nuchae and the supraspinous ligament connect the spinous processes, extending from the occiput to the sacrum.

Question 61

Curves of the vertebral column

Answer 61

* When viewed from the side, the vertebral column presents four curves: two primary and two secondaries. * The fetus in the uterus lies curled up so that the head and the knees are touching. This position shows the primary curvature. The secondary cervical curve develops when the child can hold up their head (after about 3 months) and the secondary lumbar curve develops when able to stand (after 12–15 months). The thoracic and sacral primary curves are retained.

Question 62

movement of the vertebral column

Answer 62

Movement between the individual bones of the vertebral column is very limited. However, the movements of the column are quite extensive and include flexion (bending forward), extension (bending backward), lateral flexion (bending to the side), and rotation. There is more movement in the cervical and lumbar regions than elsewhere.

Question 63

Functions of the vertebral column

Answer 63

These include: - collectively the vertebral foramina form the vertebral canal, which provides strong bony protection for the delicate spinal cord lying within it - the pedicles of adjacent vertebrae form intervertebral foramina, one on each side, providing access to the spinal cord for spinal nerves, blood vessels, and lymph vessels - the numerous individual bones with their intervertebral discs allow movement of the whole column - support of the skull - the intervertebral discs act as shock absorbers, protecting the brain - formation of the axis of the trunk, giving attachment to the ribs, shoulder girdle, and upper limbs, and the pelvic girdle and lower limbs.

Question 64

Thoracic cage

Answer 64

The thorax (thoracic cage) is formed by the sternum anteriorly, twelve pairs of ribs forming the lateral bony cages, and the twelve thoracic vertebrae.

Question 65

Sternum (breastbone)

Answer 65

* This flat bone can be felt just under the skin in the middle of the front of the chest. * The manubrium is the uppermost section and articulates with the clavicles at the sternoclavicular joints and with the first two pairs of ribs. * The body or middle portion gives attachment to the ribs. * The xiphoid process is the inferior tip of the bone. It gives attachment to the diaphragm, muscles of the anterior abdominal wall, and the Linea alba (literally ‘white line’)

Question 66

Ribs

Answer 66

* The 12 pairs of ribs form the lateral walls of the thoracic cage. They are elongated curved bones that articulate posteriorly with the vertebral column. Anteriorly, the first seven pairs of ribs articulate directly with the sternum and are known as the true ribs. The next three pairs articulate only indirectly. In both cases, costal cartilages attach the ribs to the sternum. The lowest two pairs of ribs, referred to as floating ribs, do not join the sternum at all, their anterior tips being free. * Each rib forms up to three joints with the vertebral column. Two of these joints are formed between facets on the head of the rib and facets on the bodies of two vertebrae, the one above the rib and the one below. Ten of the ribs also form joints between the tubercle of the rib and the transverse process of (usually) the lower vertebra. * The inferior surface of the rib is deeply grooved, providing a channel along which intercostal nerves and blood vessels run. Between each rib and the one below are the intercostal muscles, which move the rib cage during breathing. * Because of the arrangement of the ribs, and the quantity of cartilage present in the ribcage, it is a flexible structure that can change its shape and size during breathing. The first rib is firmly fixed to the sternum and to the 1st thoracic vertebra and does not move during inspiration. Because it is a fixed point, when the intercostal muscles contract, they pull the entire ribcage upwards towards the first rib.

Question 67

Shoulder girdle

Answer 67

The shoulder girdle consists of two clavicles and two scapulae.

Question 68

Clavicle (collar bone)

Answer 68

The clavicle is an S-shaped long bone. It articulates with the manubrium of the sternum at the sternoclavicular joint and forms the acromioclavicular joint with the acromion process of the scapula. The clavicle provides the only bony link between the upper limb and the axial skeleton.

Question 69

Scapula (shoulder blade)

Answer 69

* The scapula is a flat triangular-shaped bone, lying on the posterior chest wall superficial to the ribs and separated from them by muscles. * At the lateral angle is a shallow articular surface, the glenoid cavity, which, with the head of the humerus, forms the shoulder joint. * On the posterior surface runs a rough ridge called the spine, which extends beyond the lateral border of the scapula and overhangs the glenoid cavity. The prominent overhang, which can be felt through the skin as the highest point of the shoulder, is called the acromion process and forms a joint with the clavicle, the acromioclavicular joint, a slightly movable synovial joint that contributes to the mobility of the shoulder girdle. The coracoid process, a projection from the upper border of the bone, gives attachment to muscles that move the shoulder joint.

Question 70

Homarus

Answer 70

* This is the bone of the upper arm. The head sits within the glenoid cavity of the scapula, forming the shoulder joint. Distal to the head are two roughened projections of bone, the greater and lesser tubercles, and between them there is a deep groove, the bicipital groove or intertubercular sulcus, occupied by one of the tendons of the biceps muscle. * The distal end of the bone presents two surfaces that articulate with the radius and ulna to form the elbow joint.

Question 71

Ulna and radius

Answer 71

•These are the two bones of the forearm. The ulna is longer than and medial to the radius and when the arm is in the anatomical position, i.e., with the palm of the hand facing forward, the two bones are parallel. They articulate with the humerus at the elbow joint, the carpal bones at the wrist joint, and with each other at the proximal and distal radioulnar joints. In addition, an interosseous membrane, a fibrous joint, connects the bones along their shafts, stabilizing their association and maintaining their relative positions despite forces applied from the elbow or wrist.

Question 72

Carpal (wrist bones)

Answer 72

•There are eight carpal bones arranged in two rows of four. From outside inwards they are: -proximal row: scaphoid, lunate, triquetrum, pisiform -distal row: trapezium, trapezoid, capitate, hamate. •These bones are closely fitted together and held in position by ligaments that allow a limited amount of movement between them. The bones of the proximal row are associated with the wrist joint and those of the distal row form joints with the metacarpal bones. Tendons of muscles lying in the forearm cross the wrist and are held close to the bones by strong fibrous bands called retinacula

Question 73

Metacarpal bone (Bones of the hand)

Answer 73

These five bones form the palm of the hand. They are numbered from the thumb side inwards. The proximal ends articulate with the carpal bones and the distal ends with the phalanges.

Question 74

Phalanges (Fingers bones0

Answer 74

There are 14 phalanges, three in each finger and two in the thumb. They articulate with the metacarpal bones and with each other, by hinge joints.

Question 75

The pelvic girdle

Answer 75

The pelvic girdle is formed from two innominate (hip) bones. The pelvis is the term given to the basin-shaped structure formed by the pelvic girdle and its associated sacrum.

Question 76

Innominate (hip) bones

Answer 76

* Each hip bone consists of three fused bones: the ilium, ischium, and pubis. On its lateral surface is a deep depression, the acetabulum, which forms the hip joint with the almost spherical head of the femur. * The ilium is the upper flattened part of the bone, and it presents the iliac crest, the anterior curve of which is called the anterior superior iliac spine. The ilium forms a synovial joint with the sacrum, the sacroiliac joint, a strong joint capable of absorbing the stresses of weight-bearing and which tends to become fibrosed in later life. * The pubis is the anterior part of the bone, and it articulates with the pubis of the other hip bone at a cartilaginous joint, the symphysis pubis. * The ischium is the inferior and posterior parts. The rough inferior projections of the ischia, the ischial tuberosities, bear the weight of the body when seated. * The union of the three parts takes place in the acetabulum.

Question 77

The pelvis bones

Answer 77

The pelvis is formed by the hip bones, the sacrum and the coccyx. It is divided into upper and lower parts by the brim of the pelvis, consisting of the promontory of the sacrum and the iliopectineal lines of the innominate bones.

Question 78

Differences between the male and female pelvis

Answer 78

The shape of the female pelvis allows for the passage of the baby during childbirth. In comparison with the male pelvis, the female pelvis has lighter bones, is shallower and more rounded, and is generally roomier.

Question 79

The femur (thigh bone)

Answer 79

* The femur is the longest and heaviest bone of the body. The head is almost spherical and fits into the acetabulum of the hip bone to form the hip joint. The neck extends outwards and slightly downwards from the head to the shaft and most of it is within the capsule of the hip joint. * The posterior surface of the lower third forms a flat triangular area called the popliteal surface. The distal extremity has two articular condyles, which, with the tibia and patella, form the knee joint. The femur transmits the weight of the body through the bones below the knee to the foot.

Question 80

Tibia (shin bone)

Answer 80

* The tibia is the medial of the two bones of the lower leg. The proximal extremity is broad and flat and presents two condyles for articulation with the femur at the knee joint. The head of the fibula articulates with the inferior aspect of the lateral condyle, forming the proximal tibio­fibular joint. * The distal extremity of the tibia forms the ankle joint with the talus and the fibula. The medial malleolus is a downward projection of bone medial to the ankle joint.

Question 81

Fibula

Answer 81

The fibula is the long slender lateral bone in the leg. The head or upper extremity articulates with the lateral condyle of the tibia, forming the proximal tibiofibular joint, and the lower extremity articulates with the tibia and projects beyond it to form the lateral malleolus. This helps to stabilize the ankle joint.

Question 82

Patella (kneecap)

Answer 82

This is a roughly triangular-shaped sesamoid bone associated with the knee joint. Its posterior surface articulates with the patellar surface of the femur in the knee joint and its anterior surface is in the patellar tendon, i.e., the tendon of the quadriceps femoris muscle.

Question 83

Tarsal (ankle bones)

Answer 83

The seven tarsal bones forming the posterior part of the foot (ankle) are the talus, calcaneus, navicular, cuboid, and three cuneiform bones. The talus articulates with the tibia and fibula at the ankle joint. The calcaneus forms the heel of the foot. The other bones articulate with each other and with the metatarsal bones.

Question 84

Metatarsals (bones of the foot)

Answer 84

These are five bones, numbered from inside out, which form the greater part of the dorsum (sole) of the foot. At their proximal ends, they articulate with the tarsal bones and at their distal ends, with the phalanges. The enlarged distal head of the 1st metatarsal bone forms the ‘ball’ of the foot.

Question 85

Phalanges (toe bones)

Answer 85

There are 14 phalanges arranged in a similar manner to those in the fingers, i.e. two in the great toe (the hallux) and three in each of the other toes.

Question 86

Arches of the foot

Answer 86

The arrangement of bones in the foot, supported by associated ligaments and action of associated muscles, gives the sole of the foot an arched or curved shape. The curve running from heel to toe is called the longitudinal arch, and the curve running across the foot is called the transverse arch.

Question 87

Posterior tibialis muscle

Answer 87

This is the most important muscular support of the longitudinal arch. It lies on the posterior aspect of the lower leg, originates from the middle third of the tibia and fibula and its tendon passes behind the medial malleolus to be inserted into the navicular, cuneiform, cuboid, and metatarsal bones. It acts as a sling or ‘suspension apparatuses for the arch.

Question 88

Short muscles of the foot

Answer 88

The flexor hallucis brevis and adductor hallucis are associated with movements of the great toe. The remaining muscle, the flexor digiti minimi brevis, moves the little toe. The flexor hallucis brevis muscle is located on the medial side of the foot. It originates from two places on the sole of the foot.

Question 89

Plantar calcaneonavicular ligament (‘spring’ ligament)

Answer 89

* This is a very strong thick ligament stretching from the calcaneus to the navicular bone. It plays an important part in supporting the medial longitudinal arch. * Plantar ligaments and interosseous membranes structures support the lateral and transverse arches.

Question 90

Joints

Answer 90

A joint is a site at which any two or more bones articulate or come together. Joints allow flexibility and movement of the skeleton and allow attachment between bones.

Question 91

Fibrous joints

Answer 91

The bones forming these joints are linked with tough, fibrous material. Such an arrangement often permits no movement. For example, the joints between the skull bones, the sutures, are completely immovable, and the healthy tooth is cemented into the mandible by the periodontal ligament. The tibia and fibula in the leg are held together along their shafts by a sheet of fibrous tissue called the interosseous membrane. This fibrous joint allows a limited amount of movement and stabilizes the alignment of the bones.

Question 92

Cartilaginous joints

Answer 92

These joints are formed by a pad of tough fibrocartilage that acts as a shock absorber. The joint may be immovable, as in the cartilaginous epiphyseal plates, which in the growing child links the diaphysis of a long bone to the epiphysis. Some cartilaginous joints permit limited movement, as between the vertebrae, which are separated by the intervertebral discs, or at the symphysis pubis, which is softened by circulating hormones during pregnancy to allow for expansion during childbirth.

Question 93

Synovial joints

Answer 93

• Synovial joints are characterized by the presence of a space or capsule between the articulating bones. The ends of the bones are held close together by a sleeve of fibrous tissue and lubricated with a small amount of fluid. Synovial joints are the most moveable of the body.

Question 94

Articular or hyaline cartilage

Answer 94

The parts of the bones in contact with each other are coated with hyaline cartilage. This provides a smooth articular surface, reduces friction, and is strong enough to absorb compression forces and bear the weight of the body. The cartilage lining, which is up to 7 mm thick in young people, becomes thinner and less compressible with age. This leads to increased stress on other structures in the joint. Cartilage has no blood supply and receives its nourishment from synovial fluid.

Question 95

Capsule or capsular ligament

Answer 95

The joint is surrounded and enclosed by a sleeve of fibrous tissue which holds the bones together. It is sufficiently loose to allow freedom of movement but strong enough to protect it from injury.

Question 96

Synovial membrane

Answer 96

This epithelial layer lines the capsule and covers all non-weight-bearing surfaces inside the joint. It secretes synovial fluid.

Question 97

Synovial fluid

Answer 97

This is a thick sticky fluid, of egg-white consistency, which fills the synovial cavity. It: -nourishes the structures within the joint cavity -contains phagocytes, which remove microbes and cellular debris -acts as a lubricant -maintains joint stability -prevents the ends of the bones from being separated, as does a little water between two glass surfaces. • Little sacs of synovial fluid or bursae are present in some joints, e.g., the knee. They act as cushions to prevent friction between a bone and a ligament or tendon, or skin where a bone in a joint is near the surface.

Question 98

Extracapsular structures

Answer 98

* Ligaments that blend with the capsule stabilize the joint. * Muscles or their tendons also provide stability and stretch across the joints they move. When the muscle contracts it shortens, pulling one bone towards the other.

Question 99

Nerve and blood supply

Answer 99

Nerves and blood vessels crossing a joint usually supply the capsule and the muscles that move it.

Question 100

Types of synovial joint

Answer 100

Synovial joints are classified according to the range of movement possible or to the shape of the articulating parts of the bones involved.

Question 101

Ball and socket joints

Answer 101

The head of one bone is ball-shaped and articulates with a cup-shaped socket of another. The joint allows for a wide range of movement, including flexion, extension, adduction, abduction, rotation, and circumduction. Examples include the shoulder and hip.

Question 102

Hinge joints

Answer 102

The articulating ends of the bones fit together like a hinge on a door, and movement is therefore restricted to flexion and extension. The elbow joint is one example, permitting only flexion and extension of the forearm. Other hinge joints include the knee, ankle, and the joints between the phalanges of the fingers and toes (interphalangeal joints).

Question 103

Gliding joints

Answer 103

The articular surfaces are flat or very slightly curved and glide over one another, but the amount of movement possible is very restricted; this group of joints is the least movable of all the synovial joints. Examples include the joints between the carpal bones in the wrist, the tarsal bones in the foot, and between the processes of the spinal vertebrae (note that the joints between the vertebral bodies are the cartilaginous discs.

Question 104

Pivot joints

Answer 104

These joints allow a bone or a limb to rotate. One bone fits into a hoop-shaped ligament that holds it close to another bone and allows it to rotate in the ring thus formed. For example, the head rotates on the pivot joint formed by the dens of the axis held within the ring formed by the transverse ligament and the odontoid process of the atlas

Question 105

Condyloid joints

Answer 105

A condyle is a smooth, rounded projection on a bone and in a condyloid joint, it sits within a cup-shaped depression on the other bone. Examples include the joint between the condylar process of the mandible and the temporal bone, and the joints between the metacarpal and phalangeal bones of the hand, and between the metatarsal and phalangeal bones of the foot. These joints permit flexion, extension, abduction, adduction, and circumduction.

Question 106

Saddle joints

Answer 106

The articulating bones fit together like a man sitting on a saddle. The most important saddle joint is at the base of the thumb, between the trapezium of the wrist and the first metacarpal bone. The range of movement is like that at a condyloid joint but with additional flexibility; opposition of the thumb, the ability to touch each of the fingertips on the same hand, is due to the nature of the thumb joint.

Question 107

Shoulder joint

Answer 107

This ball and socket joint is the most mobile in the body and consequently is the least stable and prone to dislocation, especially in children. It is formed by the glenoid cavity of the scapula and the head of the humerus and is well padded with protective bursae. The capsular ligament is very loose inferiorly to allow for the free movement normally possible at this joint. The glenoid cavity is deepened by a rim of fibrocartilage, the glenoidal labrum, which provides additional stability without limiting movement. The tendon of the long head of the biceps muscle is held in the intertubercular (bicipital) groove of the humerus by the transverse humeral ligament. It extends through the joint cavity and attaches to the upper rim of the glenoid cavity.

Question 108

Elbow joint

Answer 108

* This hinge joint is formed by the trochlea and the capitulum of the humerus, and the trochlear notch of the ulna, and the head of the radius. It is an extremely stable joint because the humeral and ulnar surfaces interlock and the capsule are very strong. * Extracapsular structures consist of anterior, posterior, medial, and lateral strengthening ligaments, which contribute to joint stability. * Because of the structure of the elbow joint, the only two movements it allows are flexion and extension. The biceps is the main flexor of the forearm, aided by the brachialis; the triceps extends it.

Question 109

Proximal ad distal radioulnar joints

Answer 109

* The proximal radioulnar joint is a pivot joint formed by the rim of the head of the radius rotating in the radial notch of the ulna and is in the same capsule as the elbow joint. The annular ligament is a strong extracapsular ligament that encircles the head of the radius and keeps it in contact with the radial notch of the ulna. * The distal radioulnar joint is a pivot joint between the distal end of the radius and the head of the ulna. * Note, in addition, the presence of a fibrous membrane linking the bones along their shafts; this interosseous membrane is a type of fibrous joint and prevents separation of the bones when force is applied at either end, i.e., at the wrist or elbow. * The forearm may be pronated (turned palm down) or supinated (turned palm up). Pronation is caused by the action of the pronator teres and supination by the supinator and biceps muscles

Question 110

Wrist joint

Answer 110

* This is a condyloid joint between the distal end of the radius and the proximal ends of the scaphoid, lunate and triquetrum. A disc of white fibrocartilage separates the ulna from the joint cavity and articulates with the carpal bones. It also separates the inferior radioulnar joint from the wrist joint. * Extracapsular structures consist of medial and lateral ligaments and anterior and posterior radiocarpal ligaments.

Question 111

Joints of the hands and fingers

Answer 111

There are synovial joints between the carpal bones, between the carpal and metacarpal bones, between the metacarpal bones and proximal phalanges, and between the phalanges. Movement at the hand and finger joints is controlled by muscles in the forearm and smaller muscles within the hand. There are no muscles in the fingers; finger movements are produced by tendons extending from muscles in the forearm and the hand.

Question 112

Hip joint

Answer 112

* This ball and socket joint is formed by the cup-shaped acetabulum of the innominate (hip) bone and the almost spherical head of the femur. The capsular ligament encloses the head and most of the neck of the femur. The cavity is deepened by the acetabular labrum, a ring of fibrocartilage attached to the rim of the acetabulum, which stabilizes the joint without limiting its range of movement. The hip joint is necessarily a sturdy and powerful joint since it bears all body weight when standing. It is stabilized by its surrounding musculature, but its ligaments are also important. The three main external ligaments are the iliofemoral, pubofemoral, and sociomoral ligaments. * The lower limb can be extended, flexed, abducted, adducted, rotated, and circumducted at the hip joint.

Question 113

Knee joint

Answer 113

* This is the body's largest and most complex joint. It is a hinge joint formed by the condyles of the femur, the condyles of the tibia, and the posterior surface of the patella. The anterior part of the capsule is formed by the tendon of the quadriceps femoris muscle, which also supports the patella. Intracapsular structures include two cruciate ligaments that cross each other, extending from the intercondylar notch of the femur to the intercondylar eminence of the tibia. They help to stabilize the joint. * Semilunar cartilages or menisci are incomplete discs of white fibrocartilage lying on top of the articular condyles of the tibia. They are wedge-shaped, being thicker at their outer edges, and provide stability. They prevent lateral displacement of the bones and cushion the moving joint by shifting within the joint space according to the relative positions of the articulating bones. * Possible movements at this joint are flexion, extension, and a rotatory movement that ‘locks’ the joint when it is fully extended. When the joint is locked, it is possible to stand upright for long periods of time without tiring the knee extensors. The main muscles extending the knee are the quadriceps femoris, and the principal flexors are the gastrocnemius and hamstrings.

Question 114

Ankle joint

Answer 114

* This hinge joint is formed by the distal end of the tibia and its malleolus (medial malleolus), the distal end of the fibula (lateral malleolus), and the talus. Four important ligaments strengthen this joint: the deltoid and the anterior, posterior, medial, and lateral ligaments. * The movements of inversion and eversion occur between the tarsal bones and not at the ankle joint.

Question 115

Joints of the feet and toes

Answer 115

There are several synovial joints between the tarsal bones, between the tarsal and metatarsal bones, between the metatarsals and proximal phalanges, and between the phalanges. Movements are produced by muscles in the leg with long tendons that cross the ankle joint and by muscles of the foot. The tendons crossing the ankle joint are wrapped in synovial sheaths and held close to the bones by strong transverse ligaments. They move smoothly within their sheaths as the joints move. In addition to moving the joints of the foot, these muscles support the arches of the foot and help to maintain balance.

Question 116

Skeletal muscle

Answer 116

Muscle cells are specialized contractile cells, also called fibers. The three types of muscle tissue, smooth, cardiac, and skeletal, each differ in structure, location, and physiological function. Smooth muscle and cardiac muscle are not under voluntary control and are discussed elsewhere (smooth muscle and cardiac muscle). Skeletal muscles, which are under voluntary control, are attached to bones via their tendons and move the skeleton. Like a cardiac (but not smooth) muscle, skeletal muscle is striated (striped), and the stripes are seen in a characteristic banded pattern when the cells are viewed under the microscope.

Question 117

Organization of skeletal muscle

Answer 117

A skeletal muscle may sometimes contain hundreds of thousands of muscle fibers as well as blood vessels and nerves. Throughout the muscle, providing internal structure and scaffolding is an extensive network of connective tissue. The entire muscle is covered in a connective tissue sheath called the epimysium. Within the muscle, the cells are collected into separate bundles called fascicles, and each fascicle is covered in its own connective tissue sheath called the perimysium. Within the fascicles, the individual muscle cells are each wrapped in a fine connective tissue layer called the endomysium. •Each of these connective tissue layers runs the length of the muscle. They bind the fibers into a highly organized structure and blend together at each end of the muscle to form the tendon, which secures the muscle to bone. Often the tendon is rope-like, but sometimes it forms a broadsheet called an aponeurosis, e.g., the occipitofrontalis muscle. The multiple connective tissue layers throughout the muscle are important for transmitting the force of contraction from each individual muscle cell to its points of attachment to the skeleton.

Question 118

Skeletal muscle cells

Answer 118

* Contraction of a whole skeletal muscle occurs because of the coordinated contraction of its individual fibers. * Under the microscope, skeletal muscle cells are seen to be roughly cylindrical in shape, lying parallel to one another, with a distinctive banded appearance consisting of alternate dark and light stripes

Question 119

Actin, myosin, and sarcomeres

Answer 119

* There are two types of contractile myofilament within the muscle fiber, called thick and thin, arranged in repeating units called sarcomeres. The thick filaments, which are made of the protein myosin, correspond to the dark bands seen under the microscope. The thin filaments are made of the protein actin. Where only these are present, the bands are lighter in appearance. * Each sarcomere is bounded at each end by a dense stripe, the Z line, to which the actin fibers are attached, and lying in the middle of the sarcomere is the myosin filaments, overlapping with the actin.

Question 120

Contraction

Answer 120

The skeletal muscle cell contracts in response to stimulation from a nerve fiber, which supplies the muscle cell usually about halfway along its length. The name given to a synapse between a motor nerve and a skeletal muscle fiber is the neuromuscular junction. When the action potential spreads from the nerve along the sarcolemma, it is conducted deep into the muscle cell through a special network of channels that run through the sarcoplasm and releases calcium from the intracellular stores. Calcium triggers the binding of myosin to the actin filament next to it, forming so-called cross-bridges. ATP then provides the energy for the two filaments to slide over each other, pulling the Z lines at each end of the sarcomere closer to one another, shortening the sarcomere. This is called the sliding filament theory. If enough fibers are stimulated to do this at the same time, the whole muscle will shorten (contract)

Question 121

Motor units

Answer 121

The axons of motor neurons, carrying impulses to skele­tal muscle to produce contraction, divide into several fine filaments terminating in minute pads called synaptic knobs. The space between the synaptic knob and the muscle cell is called the synaptic cleft. Stimulation of the motor neuron releases the neurotransmitter acetylcholine, which diffuses across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic membrane on the motor endplate (the area of the muscle membrane directly across the synaptic cleft. Acetylcholine causes contraction of the muscle cell.

Question 122

The action of skeletal muscle

Answer 122

When individual muscle cells in a muscle shorten, they pull on the connective tissue framework running through the whole muscle, and the muscle develops a degree of tension (tone).

Question 123

Muscle tone

Answer 123

When a muscle fiber contracts, it obeys the all-or-none law, i.e., the whole fiber either contracts completely or not at all. The degree of contraction achieved by a whole muscle depends therefore on the number of fibers within it that are contracting at any one time, as well as how often they are stimulated. Powerful contractions involve a larger proportion of available fibers than weaker ones; to lift a heavyweight, more active muscle fibers are required than to lift a lighter one. Muscle tone is a sustained, partial muscle contraction that allows posture to be maintained without fatiguing the muscles involved.

Question 124

Muscle fatigue

Answer 124

* To work at sustained levels, muscles need an adequate supply of oxygen and fuel such as glucose. Fatigue occurs when a muscle works at a level that exceeds these supplies. The muscle response decreases with fatigue. * The chemical energy (ATP) that muscles require is usually derived from the breakdown of carbohydrates and fat; protein may be used if supplies of fat and carbohydrate are exhausted. An adequate oxygen supply is needed to fully release all the energy stored within these fuel molecules; without it, the body uses anaerobic metabolic pathways that are less efficient and lead to lactic acid production. Fatigue (and muscle pain) resulting from inadequate oxygen supply, as in strenuous exercise, occurs when lactic acid accumulates in working muscles. Fatigue may also occur because energy stores are exhausted, or due to physical injury to a muscle, which may occur after prolonged episodes of strenuous activity, e.g., marathon running.

Question 125

Muscle recovery

Answer 125

After exercise, muscle needs a period to recover, to replenish its ATP and glycogen stores, and repair any damaged fibers. For some time following exercise, depending on the degree of exertion, the oxygen debt remains (an extended period of increased oxygen demand), as the body converts lactic acid to pyruvic acid and replaces its energy stores.

Question 126

Factors affecting skeletal muscle performance

Answer 126

Skeletal muscle performs better when it is regularly exercised. Training improves endurance and power. Anaerobic training, such as weightlifting, increases muscle bulk because it increases the size of individual fibers within the muscle (hypertrophy).

Question 127

The action of skeletal muscles

Answer 127

* In order to move a body part, the muscle or its tendon must stretch across at least one joint. When it contracts, the muscle then pulls one bone towards another. For example, when the elbow is bent during flexion of the forearm, the main mover is the biceps brachii, which is anchored on the scapula at one end and on the radius at the other. When it contracts, its shortening pulls on the radius, moving the forearm up toward the upper arm and bending the elbow. * This example also illustrates another feature of muscle arrangement: that of antagonistic pairs. Many muscles/muscle groups of the body are arranged so that their actions oppose one another. Using the example of bending the elbow, when the main flexors on the front of the upper arm contract, the muscles at the back of the upper arm must simultaneously relax to prevent injury.

Question 128

Isometric and isotonic contraction

Answer 128

* In order to move a body part, the muscle or its tendon must stretch across at least one joint. When it contracts, the muscle then pulls one bone towards another. For example, when the elbow is bent during flexion of the forearm, the main mover is the biceps brachii, which is anchored on the scapula at one end and on the radius at the other. When it contracts, its shortening pulls on the radius, moving the forearm up toward the upper arm and bending the elbow. * This example also illustrates another feature of muscle arrangement: that of antagonistic pairs. Many muscles/muscle groups of the body are arranged so that their actions oppose one another. Using the example of bending the elbow, when the main flexors on the front of the upper arm contract, the muscles at the back of the upper arm must simultaneously relax to prevent injury.

Question 129

Occipitofrontalis

Answer 129

This consists of a posterior muscular part over the occipital bone (occipitalis), an anterior part over the frontal bone (frontalis), and an extensive flat tendon or aponeurosis that stretches over the dome of the skull and joins the two muscular parts. It raises eyebrows.

Question 130

Levator palpebrae superioris

Answer 130

This muscle extends from the posterior part of the orbital cavity to the upper eyelid. It raises the eyelid.

Question 131

Orbicularis oculi

Answer 131

This muscle surrounds the eye, eyelid, and orbital cavity. It closes the eye and when strongly contracted ‘screws up’ the eyes.

Question 132

Buccinator

Answer 132

This flat muscle of the cheek draws the cheeks in towards the teeth in chewing and in forcible expulsion of air from the mouth (‘the trumpeter’s muscle’).

Question 133

Orbicularis Oris

Answer 133

This muscle surrounds the mouth and blends with the muscles of the cheeks. It closes the lips and, when strongly contracted, shapes the mouth for whistling.

Question 134

Masseter

Answer 134

This broad muscle extends from the zygomatic arch to the angle of the jaw. In chewing it draws the mandible up to the maxilla, closing the jaw, exerting considerable pressure on the food.

Question 135

Temporalis

Answer 135

This muscle covers the squamous part of the temporal bone. It passes behind the zygomatic arch to be inserted into the coronoid process of the mandible. It closes the mouth and assists with chewing.

Question 136

Pterygoid

Answer 136

This muscle extends from the sphenoid bone to the mandible. It closes the mouth and pulls the lower jaw forward.

Question 137

Sternocleidomastoid

Answer 137

This muscle arises from the manubrium of the sternum and the clavicle and extends upwards to the mastoid process of the temporal bone. It assists in turning the head from side to side and is also an accessory muscle in respiration. When the muscle on one side contracts it draws the head towards the shoulder. When both contract at the same time they flex the cervical vertebrae or draw the sternum and clavicles upwards when the head is maintained in a fixed position, e.g., in forced respiration.

Question 138

Trapezius

Answer 138

This muscle covers the shoulder and the back of the neck. The upper attachment is to the occipital protuberance, the medial attachment is to the transverse processes of the cervical and thoracic vertebrae and the lateral attachment is to the clavicle and to the spinous and acromion processes of the scapula. It pulls the head backward, squares the shoulders, and controls the movements of the scapula when the shoulder joint is in use.

Question 139

Muscles of the trunk

Answer 139

These muscles stabilize the association between the appendicular and axial skeletons at the pectoral girdle and stabilize and allow movement of the shoulders and upper arms.

Question 140

Muscles of the back

Answer 140

There are six pairs of large muscles in the back, in addition to those forming the posterior abdominal wall. The arrangement of these muscles is the same on each side of the vertebral column. They are: - trapezius - latissimus dorsi - teres major - psoas - quadratus lumborum - Sacro spinalis

Question 141

Latissimus dorsi

Answer 141

This arises from the posterior part of the iliac crest and the spinous processes of the lumbar and lower thoracic vertebrae. It passes upwards across the back then under the arm to be inserted into the bicipital groove of the humerus. It adducts, medially rotates, and extends the arm.

Question 142

Teres major

Answer 142

This originates from the inferior angle of the scapula and is inserted into the humerus just below the shoulder joint. It extends, adducts, and medially rotates the arm.

Question 143

Quadratus lumborum

Answer 143

This muscle originates from the iliac crest, then it passes upwards, parallel, and close to the vertebral column and is inserted into the 12th rib. Together the two muscles fix the lower rib during respiration and cause extension of the vertebral column (bending backward). If one muscle contracts, it causes lateral flexion of the lumbar region of the vertebral column.

Question 144

Sacro spinalis (erector spinae)

Answer 144

This is a group of muscles lying between the spinous and transverse processes of the vertebrae. They originate from the sacrum and are finally inserted into the occipital bone. Their contraction causes extension of the vertebral column.

Question 145

Muscles of the abdominal wall

Answer 145

•Five pairs of muscles form the abdominal wall. From the surface inwards they are: -rectus abdominis -external oblique -internal oblique -transversus abdominis -quadratus lumborum •The main function of these paired muscles is to form the strong muscular anterior wall of the abdominal cavity. When the muscles contract together, they: -compress the abdominal organs -flex the vertebral column in the lumbar region •Contraction of the muscles on one side only bends the trunk towards that side. Contraction of the oblique muscles on one side rotates the trunk. •The anterior abdominal wall is divided longitudinally by a very strong midline tendinous cord, the linea alba (meaning ‘white cord’) which extends from the xiphoid process of the sternum to the symphysis pubis.

Question 146

Rectus abdominals

Answer 146

This is the most superficial muscle. It is broad and flat, originating from the transverse part of the pubic bone then passing upwards to be inserted into the lower ribs and the xiphoid process of the sternum. Medially the two muscles are attached to the linea alba.

Question 147

External oblique

Answer 147

This muscle extends from the lower ribs downwards and forward to be inserted into the iliac crest and, by an aponeurosis, to the linea alba.

Question 148

Internal oblique

Answer 148

This muscle lies deep to the external oblique. Its fibers arise from the iliac crest and by a broad band of fascia from the spinous processes of the lumbar vertebrae. The fibers pass upwards towards the midline to be inserted into the lower ribs and, by an aponeurosis, into the linea alba. The fibers are at right angles to those of the external oblique.

Question 149

Transverse abdominals

Answer 149

This is the deepest muscle of the abdominal wall. The fibers arise from the iliac crest and the lumbar vertebrae and pass across the abdominal wall to be inserted into the linea alba by an aponeurosis. The fibers are at right angles to those of the rectus abdominis.

Question 150

Inguinal canal

Answer 150

•This canal is 2.5–4 cm long and passes obliquely through the abdominal wall. It runs parallel to and immediately in front of the transversal fascia and part of the inguinal ligament. In the male, it contains the spermatic cord and, in the female, the round ligament. It constitutes a weak point in the otherwise strong abdominal wall through which herniation may occur.

Question 151

Muscles of the pelvic floor

Answer 151

* The pelvic floor is divided into two identical halves that unite along the midline. Each half consists of fascia and muscle. The muscles are the Levator ani and the coccygeus. * The pelvic floor supports the organs of the pelvis and maintains continence, i.e., it resists raised intrapelvic pressure during micturition and defecation.

Question 152

Levator ani

Answer 152

This is a pair of broad flat muscles, forming the anterior part of the pelvic floor. They originate from the inner surface of the true pelvis and unite in the midline. Together they form a sling that supports the pelvic organs.

Question 153

Coccygeus

Answer 153

This is a paired triangular sheet of muscle and tendinous fibers situated behind the Levator ani. They originate from the medial surface of the ischium and are inserted into the sacrum and coccyx. They complete the formation of the pelvic floor, which is perforated in the male by the urethra and anus, and in the female by the urethra, vagina, and anus.

Question 154

Deltoid

Answer 154

These muscle fibers originate from the clavicle, acromion process, and spine of the scapula and radiate over the shoulder joint to be inserted into the deltoid tuberosity of the humerus. It forms the fleshy and rounded contour of the shoulder, and its main function is the movement of the arm. The anterior part causes flexion, the middle or main part abduction and the posterior part extends and laterally rotates the shoulder joint.

Question 155

Pectoralis major

Answer 155

This lies on the anterior thoracic wall. The fibers originate from the middle third of the clavicle and from the sternum and are inserted into the lip of the intertubercular groove of the humerus. It draws the arm forward and towards the body, i.e., flexes and adducts.

Question 156

Coracobrachialis

Answer 156

This lies on the upper medial aspect of the arm. It arises from the coracoid process of the scapula, stretches across in front of the shoulder joint, and is inserted into the middle third of the humerus. It flexes the shoulder joint.

Question 157

Biceps

Answer 157

This lies on the anterior aspect of the upper arm. At its proximal end, it is divided into two parts (heads), each of which has its own tendon. The short head arises from the coracoid process of the scapula and passes in front of the shoulder joint to the arm. The long head originates from the rim of the glenoid cavity and its tendon passes through the joint cavity and the bicipital groove of the humerus to the arm. It is retained in the bicipital groove by a transverse humeral ligament that stretches across the groove. The distal tendon crosses the elbow joint and is inserted into the radial tuberosity. It helps to stabilize and flex the shoulder joint and at the elbow joint, it assists with flexion and supination.

Question 158

Brachialis

Answer 158

This lies on the anterior aspect of the upper arm deep to the biceps. It originates from the shaft of the humerus, extends across the elbow joint, and is inserted into the ulna just distal to the joint capsule. It is the main flexor of the elbow joint.

Question 159

Triceps

Answer 159

•This lies on the posterior aspect of the humerus. It arises from three heads, one from the scapula and two from the posterior surface of the humerus. The insertion is by a common tendon to the olecranon process of the ulna. It helps to stabilize the shoulder joint, assists in adduction of the arm, and extends the elbow joint.

Question 160

Brachioradialis

Answer 160

The brachioradialis spans the elbow joint, originating on the distal end of the humerus and inserts on the lateral epicondyle of the radius. Contraction flexes the elbow joint.

Question 161

Prontor teres

Answer 161

This lies obliquely across the upper third of the front of the forearm. It arises from the medial epicondyle of the humerus and the coronoid process of the ulna and passes obliquely across the forearm to be inserted into the lateral surface of the shaft of the radius. It rotates the radioulnar joints, changing the hand from the anatomical to the writing position, i.e., pronation.

Question 162

Supinator

Answer 162

This lies obliquely across the posterior and lateral aspects of the forearm. Its fibers arise from the lateral epicondyle of the humerus and the upper part of the ulna and are inserted into the lateral surface of the upper third of the radius. It rotates the radioulnar joints, often with help from the biceps, changing the hand from the writing to the anatomical position, i.e., supination.

Question 163

Flexor carpi radialis

Answer 163

This lies on the anterior surface of the forearm. It originates from the medial epicondyle of the humerus and is inserted into the second and third metacarpal bones. It flexes the wrist joint, and when acting with the extensor carpi radialis, abducts the joint.

Question 164

Pronator quadratus

Answer 164

This square-shaped muscle is the main muscle causing pronation of the hand and has attachments on the lower sections of both the radius and the ulna.

Question 165

Flexor carpi ulnaris

Answer 165

This lies on the medial aspect of the forearm. It originates from the medial epicondyle of the humerus and the upper parts of the ulna and is inserted into the pisiform, the hamate, and the fifth metacarpal bones. It flexes the wrist, and when acting with the extensor carpi ulnaris, adducts the joint.

Question 166

Extensor carpi radialis longus and brevis

Answer 166

These lie on the posterior aspect of the forearm. The fibers originate from the lateral epicondyle of the humerus and are inserted by a long tendon into the second and third metacarpal bones. They extend and abduct the wrist.

Question 167

Extensor carpi ulnaris

Answer 167

This lies on the posterior surface of the forearm. It originates from the lateral epicondyle of the humerus and is inserted into the fifth metacarpal bone. It extends and adducts the wrist.

Question 168

Palmaris longus

Answer 168

This muscle resists shearing forces that might pull the skin and fascia of the palm away from the underlying structures and flexes the wrist. Its origin is on the medial epicondyle of the humerus, and it inserts on tendons on the palm of the hand.

Question 169

Extensor digitorum

Answer 169

This muscle originates on the lateral epicondyle of the humerus and spans both the elbow and wrist joints; in the wrist, it divides into four tendons, one for each finger. The action of this muscle can extend any of the joints across which it passes, i.e., the elbow, wrist, or finger joints.

Question 170

The muscle that controls finger movements

Answer 170

Large muscles in the forearm that extend to the hand give power to the hand and fingers, but not the delicacy of movement needed for fine and dexterous finger control. Smaller muscles, which originate on the carpal and metacarpal bones, control tiny and precise finger movements via tendinous attachments on the phalanges; muscle fibers do not extend into the fingers.

Question 171

Muscle of the hip and lower limb

Answer 171

The biggest muscles of the body are found here since their function is largely weight-bearing. The lower parts of the body are designed to transmit the force of body weight in walking, running, etc., evenly throughout weight-bearing structures, and act as shock absorbers.

Question 172

Psoas

Answer 172

This arises from the transverse processes and bodies of the lumbar vertebrae. It passes across the flat part of the ilium and behind the inguinal ligament to be inserted into the femur. Together with the iliacus it flexes the hip joint.

Question 173

Iliacus

Answer 173

This lies in the iliac fossa of the innominate bone. It originates from the iliac crest, passes over the iliac fossa, and joins the tendon of the psoas muscle to be inserted into the lesser trochanter of the femur. The combined action of the iliacus and psoas flexes the hip joint.

Question 174

Quadriceps femoris

Answer 174

This is a group of four muscles lying on the front and sides of the thigh. They are the rectus femoris and three vasti: lateral, medial, and intermedius. The rectus femoris originates from the ilium and the three vasti from the upper end of the femur. Together they pass over the front of the knee joint to be inserted into the tibia by the patellar tendon. Only the rectus femoris flexes the hip joint. Together, the group acts as a very strong extensor of the knee joint.

Question 175

Obturators

Answer 175

The obturators, deep muscles of the buttock, have their origins in the rim of the obturator foramen of the pelvis and insert into the proximal femur. Their main function lies in lateral rotation at the hip joint.

Question 176

Gluteal

Answer 176

These consist of the gluteus maximus, medius, and minimums, which together form the fleshy part of the buttock. They originate from the ilium and sacrum and are inserted into the femur. They cause extension, abduction, and medial rotation at the hip joint.

Question 177

Sartorius

Answer 177

This is the longest muscle in the body and crosses both the hip and knee joints. It originates from the anterior superior iliac spine and passes obliquely across the hip joint, thigh, and knee joint to be inserted into the medial surface of the upper part of the tibia. It is associated with flexion and abduction at the hip joint and flexion at the knee.

Question 178

Adductor group

Answer 178

This lies on the medial aspect of the thigh. They originate from the pubic bone and are inserted into the linea aspera of the femur. The adduct and medially rotate the thigh.

Question 179

Hamstring

Answer 179

These lie on the posterior aspect of the thigh. They originate from the ischium and are inserted into the upper end of the tibia. They are the biceps femoris, semimembranosus, and semitendinosus muscles. They flex the knee joint.

Question 180

Gastrocnemius

Answer 180

This forms the bulk of the calf of the leg. It arises by two heads, one from each condyle of the femur, and passes down behind the tibia to be inserted into the calcaneus by the calcanean tendon (Achilles’ tendon). It crosses both knee and ankle joints, causing flexion at the knee and plantarflexion (rising onto the ball of the foot) at the ankle.

Question 181

Anterior tibialis

Answer 181

This originates from the upper end of the tibia, lies on the anterior surface of the leg, and is inserted into the middle cuneiform bone by a long tendon. It is associated with dorsiflexion of the foot.

Question 182

Soleus

Answer 182

This is one of the main muscles of the calf of the leg, lying immediately deep to the gastrocnemius. It originates from the heads and upper parts of the fibula and the tibia. Its tendon joins that of the gastrocnemius so that they have a common insertion into the calcaneus by the calcanean (Achilles) tendon. It causes plantar flexion at the ankle and helps to stabilize the joint when standing.