VERTEBRAL COLUMN

VERTEBRAL COLUMN

Vertebral column is made by 26 bones.

24 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 to five small fused vertebrae, and lastly the coccyx, or tail, which is formed from between three to 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 twelve vertebrae are the thoracic spine and the next five 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 called C1, and the third lumbar vertebra is called L3.

The movable vertebrae have many characteristics in common, but some groups have distinguishing features.

CHARACTERISTICS OF A TYPICAL VERTEBRA

THE BODY.

 The body of each vertebra is situated anteriorly. 

The size varies with the site. 

They are smallest in the cervical region and become larger towards the lumbar region.

THE VERTEBRAL (NEURAL) ARCH.

 This enclosed a large vertebral foramen.

 It is the area 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 called transverse process, and where the two laminae meet at the back is a process called the spinous process. 

These are the bony prominences that can be felt through the skin along the length of the spine. 

The neural arch has four articular surfaces; two articulate with the vertebra above the two with the one below.

 The vertebral foramina form the vertebral (neural) canal that contains the spinal cord.

REGION-SPECIFIC VERTEBRAL CHARACTERISTICS

CERVICAL VERTEBRAE

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 typical.

The first cervical vertebra, 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 occipigtal 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 occupied 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 seventh cervical vertebra C7, is also known as the vertebra prominens.

 It possesses a long spinous prominence terminating in a swollen tubercle, which is easily felt at the base of the neck.

THORACIC VERTEBRAE.

The thoracic vertebrae are larger than the cervical vertebrae because this section of the vertebral column has to support more body weight. 

The bodies and transverse process have facets for articulation with the ribs.

LUMBAR VERTEBRAE.

These are the largest of the vertebrae because they have to support the weight of the upper body. They have to support the weight of the upper body.

 They have substantial spinous processes for muscle attachment.

SACRUM.

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 5^th 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 or foramina for the passage of nerves.

COCCYX

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.

FEATURES OF THE VERTEBRAL COLUMN

INTERVERTEBRAL DISCS

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 as a whole.

INTERVERTEBRAL FORAMINA.

When two adjacent vertebrae 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 intervetebral foramen on each side between every pair of vertebrae, through which the spine nerves, blood vessels and lymph vessels pass.

LIGAMENTS OF THE VERTEBRAL COLUMN.

These ligaments hold the vertebrae together and keep the intervertebral discs in position.

The transverse ligament maintains 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 connect the laminae of adjacent vertebrae.

The ligamentum nuchae and the supraspinous ligament connect the spinous processes, extending from the occiput to the sacrum.

CURVES OF THE VERTEBRAL COLUMN.

When viewed from the side, the vertebral column presents four curves: two primary and two secondary.

The fetus in the uterus lies curled up so that the head and the knees are more or less touching.

 This position shows primary curvature. 

The secondary cervical curve develops when the child can hold up his head (after about 3 months) and the secondary lumbar curve develops when he stands upright (after 12 to 15 months). 

The thoracic and sacral primary curves are retained.

MOVEMENTS OF THE VERTEBRAL COLUMN

The movements between the individual bones of the vertebral column and very limited. However, the movements of the column as a whole 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.

FUNCTIONS OF THE VERTEBRAL COLUMN

These include the following:

·         Collectively the vertebral foramina form the vertebral canal, which provides a 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 enable a certain amount of movement.

·         It supports the skull.

·         The intervertebral discs act as shock absorbers, protecting the brain.

·         It forms the axis of the trunk, giving attachment to the ribs, shoulder girdle and upper limbs, and the pelvic girdle and lower limbs.

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