Classification of skeleton: Axial-3

Features of the Vertebral Column

• Intervertebral Discs: The bodies of adjacent vertebrae are separated by intervertebral discs that consist 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 lumber region. They allow movements of the verterbral column and absorb the vertebral shock
• Intervertebral Foramina: When two adjacent vertebral are viewed from the side, a foramen formed by a gap between the vertebral pedicles, can be seen. Half of the wall is formed by the vertebra above, and half by the one below. Throughout the length of the column, there is an intervertebral foramen on each side between every pair of vertebra, through which the spinal nerves, blood vessels and lymph vessels pass.

Movement of the Vertebral Column

The vertebral column when viewed from side is not a straight line rather have bendings. These are normal curves of the vertebral column. There are 4 normal curves formed by vertebras, two are concave and the other two are convex. The presences of the curve have several functions; absorption of shock, maintenance of balance, protection of column from fracture and increasing the strength of the column. In the age of the fetus, there is only a single anterior concave curve. But approximately at the third post natal month, when the child begins to hold head erect, the cervical curve develops. Later when the child sits up, stands and walks, the lumbar curve develops. The cervical and lumbar curves are an anteriorly convex and because they are modification of the fetal position they are called secondary curves. The thoracic and sacral curves are anteriorly concave, since they retain the anterior concavity of the fetal curve they are referred primary curves.

Functions of the Vertebral Column

• It supports the skull.
• It forms the axis of the trunk, giving attachment to the ribs, shoulder and upper limbs and the pelvic girdle and lower limbs.
• The intervertebral disc act as a shock absorbers that protect brain and spinal cord. Collectively the vertebral foramina form the vertebral canal, which provides a strong bony protection for the spinal cord lying within it.
• The numerous individual bones with their intervertebral disc allow movement of the whole column.
• The pedicles of adjacent vertebrae form intervertebral foramina one on each side, through which spinal nerves, blood, vessels and lymph vessels pass.

Thorax

The thorax (rib cage) consists of 12 pairs of ribs and the sternum or breastbone. It forms a conical enclose for the heart, lungs and also protects spleen, liver and kidney. It provides attachment for the upper extremities and pectoral girdle. The floor is formed by the diaphragm, the wall is covered with muscle and skin and has narrow superior apex and broad base. The rib cage is rhythmically expanded by the respiratory muscles for respiration.

Sternum

The sternum or breast bone can be felt just under the skin in the middle of the front of the chest. It is about 15-17 cm long and made up of the manubrium (superior portion), a body (middle and largest portion) and a xiphoid process(inferior and smallest portion). The manubrium is roughly trapezoidal bone. Manubrium is the widest and thickest part of sternum. The manubrium articulates with the clavicles at the sterno-clavicular joints and with the first two pains of ribs. The body or middle portion gives attachment to the ribs. The xiphoid process is the tip of the bone and gives attachment to the diaphragm, muscles of the anterior abdominal wall. The junction of the manubrium and the body forms the sternal angle. The manubrium on its superior portion has a depression called jugular (supra sternal) notch. On each side of the jugular notch are clavicular notch that articulates with medial end of clavicle. Body is located at the level of T5-T9 vertebrae.

Ribs

There are 12 pains of ribs which forms lateral wall of the thoracic cage. They are long, slender and curved bone that articulate posteriorly with the vertebral column. The first 7 pairs of ribs are attached directly to the sternum by separate costal cartilages. Ribs, 8, 9 and 10 attach to the costal cartilage of the 7th rib and rib 11, 12th do not attach to anything inferiorly but are embedded in thoracic muscles. The ribs that have costal cartilages and attach directly to the sternum are called true ribs. The first seven pairs are called true ribs. The remaining five pairs are called false ribs because their cartilages either attach indirectly to the sternum or do not attach at all. The 11th and 12th ribs are also designated as floating ribs because their anterior part even doesn't attach indirectly to sternum. The space between ribs are called intercostals spaces. Although there is variation when we examine, a typical rib (3rd to 9th) contains a head, neck, tubercle and body parts. The head is a projection at posterior end of the rib. It consist one or two facet that articulate with facet of the vertebra. The neck is constricted portion just lateral to the head. One or two knob like structures on the posterior end where the neck joins the body is the tubercles, which articulate with the transverse process of the vertebra and to attach with muscles of the trunk. The body (shaft) is main part of the rib. The costal angle is the site where the rib changes its direction. The inner side of the costal angle is costal grove, where thoracic nerves and blood vessels are protected. Atypical ribs are 1st, 2nd and 10th - 12th ribs. 1st rib is broadest, shortest and most sharply curved.