FUNCTIONS OF THE VERTEBRAL COLUMN

THE SKELETON

The skeleton (Fig. 3.26) is the bony framework of the body. It forms the cavities and fossae (depressions or hollows) that protect some structures, forms the joints and gives attachment to muscles. A detailed description of the bones is given in Chapter 16. Table 16.1 (p. 388) lists the terminology related to the skeleton.

The skeleton is described in two parts: axial and appendicular (the appendages attached to the axial skeleton).

AXIAL SKELETON

The axial skeleton (axis of the body) consists of the skull, vertebral column, sternum (or breast bone) and the ribs.

SKULL

The skull is described in two parts, the cranium, which contains the brain, and the face. It consists of a number of bones, which develop separately but fuse together as they mature. The only movable bone is the mandible or lower jaw. The names and positions of the individual bones of the skull can be seen in Figure 3.27.

Functions of the skull

The various parts of the skull have specific and different functions (see p. 395) and are, in summary:

• protection of delicate structures including the brain, eyes and inner ears

• maintaining patency of the nasal passages enabling breathing

• eating - the teeth are embedded in the mandible and maxilla; and movement of the mandible, the only movable skull bone, allows chewing.

VERTEBRAL COLUMN

This consists of 24 movable bones (vertebrae) plus the sacrum and coccyx. The bodies of the bones are separated

from each other by intervertebral discs, consisting of cartilage. The vertebral column is described in five parts and the bones of each part are numbered from above downwards (Fig. 3.28):

• 7 cervical

• 12 thoracic

• 5 lumbar

• 1 sacrum (5 fused bones)

• 1 coccyx (4 fused bones).

The first cervical vertebra, called the atlas, forms a joint {articulates) with the skull. Thereafter each vertebra forms a joint with the vertebrae immediately above and below. More movement is possible in the cervical and lumbar regions than in the thoracic region.

The sacrum consists of five vertebrae fused into one bone that articulates with the fifth lumbar vertebra above, the coccyx below and an innominate (pelvic or hip) bone at each side.

The coccyx consists of the four terminal vertebrae fused into a small triangular bone that articulates with the sacrum above.

FUNCTIONS OF THE VERTEBRAL COLUMN

The vertebral column has several important functions:

• It protects the spinal cord. In each vertebra is a hole, the vertebral foramen, and collectively the foramina form a canal in which the spinal cord lies.

• Adjacent vertebrae form openings (intervertebral foramina), which protect the spinal nerves as they pass from the spinal cord (see Fig. 16.24, p. 398).

• In the thoracic region the ribs articulate with the vertebrae forming joints allowing movement of the ribcage during respiration.

THORACIC CAGE

The thoracic cage is formed by:

• 12 thoracic vertebrae

• 12 pairs of ribs

• 1 sternum or breast bone.

The arrangement of the bones is shown in Figure 3.29.

Date: 2015-12-11; view: 1154