Axial Skeleton-Vertebral Column, Thoracic cage
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 -
- 7 cervical
- 12 thoracic
- 5 lumbar
- 1 sacrum (5 fused bones)
- 1 coccyx (4 fused bones).
The first cervical vertebra, called the atlas, articulates with the skull.
Functions of the vertebral column -
- It protects the spinal cord. In each bone there is a hole or foramen and when the vertebrae are arranged one above the other, the foramina form a canal. The spinal cord, which is an extension of nerve tissue from the brain, lies in this canal.
- Adjacent vertebrae form openings (intervertebral foramina) through which spinal nerves pass from the spinal cord to all parts of the body are 31 pairs of spinal nerves.
- In the thoracic region the ribs articulate with the vertebrae forming joints which move during respiration.
The thoracic cage is formed by-
- 12 thoracic vertebrae
- 12 pairs of ribs
- 1 sternum or breast bone.
Functions of the thoracic cage -
- It protects the thoracic organs. The bony framework protects the heart, lungs, large blood vessels and other structures.
- It forms joints between the upper limbs and the axial skeleton. The upper part of the sternum, the manubrium, articulates with the clavicles forming the only joints between the upper limbs and the axial skeleton.
- It gives attachment to the muscles of respiration:
- intercostal muscles occupy the spaces between the ribs and when they contract the ribs move upwards and outwards, increasing the capacity of the thoracic cage, and inspiration (breathing in) occurs.
- the diaphragm is a dome-shaped muscle which separates the thoracic and abdominal cavities. It is attached to the bones of the thorax and when it contracts it assists with inspiration. Structures which extend from one cavity to the other pass through the diaphragm
- It enables breathing (ventilation) to take place.