Bone

Bone is a living hard tissue capable of changing its structure as the result of the stresses to which it is subjected.

consists of cells, fibers, and matrix

It is hard because of the calcification of its extracellular matrix and possesses a degree of elasticity because of the presence of organic

fibers.

Functions of bones:

Form the supporting skeleton of the body.Bone has a protective function; the skull and vertebral column, for example protect the brain and spinal cord, the sternum and ribs protect the thoracic and upper abdominal viscera. Through the attached muscle, it serves as a lever, as seen in the long bones of the limbs It is important storage area for calcium salts. Its cavities the delicate blood-forming bone marrow, which manufactures blood cell.

Bone exists in two forms:

Compact bone appears as a dense, hard, protective layer which covers the outer surface of bones. Cancellous (spongy) bone consists of a branching network of trabeculae. The trabeculae are arranged in such a manner as to resist the stresses and strain to which the bone is exposed.

The bones of the adult skeleton No. 200, or 206 if the three tiny bones of each ear (the auditory ossicles,) are included in the total.

the axial skeleton the appendicular skeleton

Parts of the bony skeleton:

Axial skeleton

The skull: The skull is made up of 22 bones, one of which is mobile the mandible or lower jaw, the remaining 21 skull bones formed of cranium.

The hyoid bone

The vertebrae forming the vertebral column

consists of individual vertebra connected, one above the other, by cartilaginous intervertebral discs and by ligaments and small joints.

The whole adult vertebral column consists of 32-34 bones, compared with 33 in the fetus. There are:

7 cervical vertebrae in the neck

12 thoracic vertebrae in the thorax

5 lumbar vertebrae

the sacrum representing the fusion

of the 5 sacral of the fetus.

the coccyx, representing the

fusion of 3-5 coccygeal vertebrae of

the fetus.

The ribs: 12 pairs of ribs

The sternum

Periphearl skeleton (appendicular)

32 in each upper limb

31 in each lower limb

the limb girdles: the bones that

connect the limb to the axial

skeleton.

Upper limb bones

The shoulder girdle (also called the pectoral girdle) consists of the clavicle and the scapula

The bones of the arm are the humerus

The radius and the ulna (the bones of the forearm)

The carpal bones (the wrist bones), the metacarpal bones and the phalanges (the bones of the hand)

Lower limb bones

The hip girdle (also called the pelvic girdle) in the adult is the single hip bone, which consists of three bones (the ilium, the ischium and the pubis) that have become fused together during embryonic development.

The femur (the thigh bone)

The tibia and fibula (the bones of the leg).

The tarsal and metatarsal bones and the phalanges (the bones of the foot).

CLASSIFICATION OF BONES

general shape grouped as follows

Long bones are found in the limbs e.g. the humerus, femur, metacarpals, metatarsals, and phalanges. Their length is greater than their breadth. They have a tubular shaft. The diaphysis, and usually an epiphysis at each end. During the growing phase, the diaphysis is separated from the epiphysis by an epiphysis cartilage. The part of the diaphysis that lies adjacent to the epiphyseal cartilage is called the metaphysic.

The shaft has a central marrow cavity containing bone marrow. The outer part of the shaft is composed of compact bone that is covered by a connective tissue sheath, the periosteum. The ends of long bones are composed of cancellous bone surrounded by a thin layer of compact bone. The articular surfaces of the ends of the bones are covered by hyaline cartilage.

Short bones are found in the hand and foot (e.g. the scaphoid, carpal, tarsal, and calcaneum). They are

roughly cuboidal in shape and are composed of cancellous bone surrounded by a thin layer of compact bone. Short bones are covered with

periosteum, and the articular surfaces are covered by hyaline cartilage.

Flat bones are found in the vault of the skull (e.g. the frontal and parietal bones). They are comosed of thin inner and outer layers of compact bone, the tables, separated by a layer of cancellous bone.

Irragular bones include those not assigned to the previous group (e.g. the bones of the skull. The vertebrae, and the pelvic). They are compose of a thin shell of compact bone with an interior made up of cancellous bone.

Sesamoid bones are small nodules of bone that are found in certain tendons where they rub over bony

surfaces. The great part of a sesamoid bone is buried in the tendon, and the free surface is covered with

cartilage, the largest sesamoid bone is the patella, which is located in the tendon of the quadriceps femoris. Other

examples are found in the tendons of the flexor pollicis brevis and flexor hallucis brevis. The function of a

sesamoid bone is to reduce friction on the tendon; it can also alter the direction of pull of a tendon.

Development of Bone

Bone formation starts as early as the 5th week of intrauterine foetal life by the appearance of primary centers of ossification.

After birth another generation of centers appears the secondary centers of ossification.

Membranous

the bone is developed directly from a connective tissue membrane. The bones of the vault of the skull are developed rapidly by the membranous method in the embryo, and this serves to protect the underlying developing brain. At birth, small areas of membrane persist between the bones. This is important clinically because it allows the bones a certain amount of mobility, so that the skull can undergo molding during its descent through the female genital passages. Other bone developed by membranous is the clavicle.

Endochondral (cartilaginous)

A cartilaginous model is first laid down and is later replaced by bone. The long bones of the limbs are developed by endochondral ossification, which is a

slow process that is not completed until the eighteenth to twentieth year or even later. The

center of bone formation found in the shaft of the bone is referred to as the diaphysis; the centers at

the ends of the bone, as the epiphyses. The plate of cartilage at each end, lying between the epiphysis

and diaphysis in a growing bone, is called the epiphyseal plate. The metaphysis is that part of the

diaphysis that abuts onto the epiphyseal plate.

Functions of periosteum

Gives attachments to muscles, tendons, ligaments and capsule.Essential for the blood supply of bone.Growth of bone in width.Necessary for healing of fractures.

Surface markings of bones

The surfaces of bones show various marking or irregularities. Where bands of fascia, ligament, tendon, or aponeurosis are attached to bone. The surface is raised or roughened. These roughenings are not present at birth. They appear at puberty and become progressively more obvious during adult life. The pull of these fibrous structures causes the periosteum to raised and new bone to be deposited beneath.

Elevations

Line: Faint linear elevation.

Ridge: Sharp linear elevation.

Border: line or ridge which separates two surfaces.

Crest: free projecting ridge.

Process: Projection from the surface of bone.

Tubercle: Rounded small process.

Spine: Pointes process

Tuberosity: Large tubercle for muscle attachment.

Trochanter: Large tuberosity with square cut surfaces.

Depressions

Fossa: Broad depression below the surface.

Groove or sulcus: Elongated depression with two edges.

Notch: Deficient part of a border.

Perforations

Foramen: Hole connecting two surfaces.

Canal: Tubular passage with two openings.

Hiatus: narrow passage with a visible end and a hidden end.

Fissure: Cleft between two bones.

Articular surface

Head: Rounded end of a bone.

Neck: Constricted following the head.

Condyle: oval projection.

Trochles: Pulley-like projection.

Facet: Small circumscribed surface.