Vertebral Column-Structure & Functions

STRUCTURE AND FUNCTIONS OF VERTEBRAL COLUMN

Vertebral Column Curvatures

The Vertebral Column

The adult vertebral column typically consists of 33 vertebrae arranged in five regions: 7cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal.

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The typical vertebrae consists of

Body, transverse process, the foramen transversarium, the vertebral foramen and spinous process The vertebral column (spine), extending from the cranium (skull) to the apex of the coccyx.

Vertebral Column-Structure & Functions

• The vertebral column protects the spinal cord and spinal nerves, supports the weight of the body superior to the level of the pelvis, provides a partly rigid and flexible axis for the body and a pivot for the head, and plays an important role in posture and locomotion.

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Significant motion occurs between only the superior 25 vertebrae.

The 5 sacral vertebrae are fused in adults to form the sacrum, and the 4 coccygeal vertebrae are fused to form the coccyx.

Vertebral Column-Structure & Functions

The vertebrae gradually become larger as the vertebral column descends to the sacrum and then become progressively smaller toward the apex of the coccyx.

These structural differences are related to the fact that the successive vertebrae bear increasing amounts of the body's weight CT

Curvatures of Vertebral Column

The vertebral column in adults has four curvatures: cervical, thoracic, lumbar, and sacral The curvatures provide a flexible support (shock-absorbing resilience) for the body.

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The thoracic and sacral curvatures are concave anteriorly, whereas the cervical and lumbar curvatures are concave posteriorly.

The thoracic and sacral curvatures are primary curvatures, developing during the fetal period.

VERTEBRAL COLUMN

C1 & C2

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Vertebral Column-Structure & Functions

Primary curvatures are retained throughout life as a consequence of differences in height between the anterior and the posterior parts of the vertebrae.

The cervical and lumbar curvatures are secondary curvatures, which begin to appear in the cervical region during the fetal period but do not become obvious until infancy.

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Secondary curvatures are maintained primarily by differences in thickness between the anterior and the posterior parts of the IV discs.

The cervical curvature becomes prominent when an infant begins to hold his or her head erect.

Vertebral Column-Structure & Functions

The lumbar curvature becomes obvious when an infant begins to walk and assumes the upright posture. This curvature, generally more pronounced in females, ends at the lumbosacral angle, formed at the junction of the L5 vertebra with the sacrum.

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The sacral curvature of females is reduced so that the coccyx protrudes less into the pelvic outlet.

The curvatures provide additional flexibility (shock-absorbing resilience) to the vertebral column, augmenting that provided by the IV discs

Structure and Function of Vertebrae

Vertebrae vary in size and other characteristics from one region of the vertebral column to another and to a lesser degree within each region.

A typical vertebra consists of a vertebral body, vertebral arch, and seven processes.

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The vertebral body gives strength to the vertebral column and supports body weight.

The size of vertebral bodies, especially from T4 inferiorly, increases to bear the progressively greater body weight.

Vertebral Column-Structure & Functions

In life, most of the superior and inferior surfaces of vertebral bodies are covered with hyaline cartilage, which are remnants of the cartilaginous model from which the bone develops, except at the periphery where there is a ring of smooth bone, the epiphysial rim.

The cartilaginous remnants permit some diffusion of fluid between the IV disc and capillaries in the vertebral body.

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The vertebral arch lies posterior to the vertebral body and is formed by right and left pedicles and laminae.

The pedicles are short, stout processes that join the vertebral arch to the vertebral body.

The pedicles project posteriorly to meet two broad, flat plates of bone, called laminae, which unite in the midline.

The vertebral arch and the posterior surface of the vertebral body form the walls of the vertebral foramen.

The succession of vertebral foramina in the articulated column forms the vertebral canal, which contains the spinal cord, meninges (protective membranes), fat, spinal nerve roots, and vessels.

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The indentations formed by the projection of the body and articular processes superior and inferior of the pedicles are vertebral notches The superior and inferior vertebral notches of adjacent vertebrae contribute to the formation of the IV foramina, which give passage to spinal nerve roots and accompanying vessels and contain the spinal ganglia

Seven Processes Arise From the Vertebral Arch of a Typical Vertebra

• One median spinous process projects posteriorly from the vertebral arch
• Two transverse processes project posterolaterally

Four articular processes two superior and two inferior

Functions of the Vertebral Column

Strong bone protection for the delicate spinal cord The intervertebral foramina one on each side providing access to the spinal cord for spinal nerves, blood vessels and lymph vessels It enables certain amount of movements It support the skull

Intervertebral disc acts as shock absorber It forms the axis of the trunk giving attachment to the ribs, shoulder, girdle and upper limbs and pelvic girdle and the lower limb

Sacrum and Cocygeal Vertebrae

The large, wedge-shaped sacrum in adults is composed of five fused sacral vertebrae.

The sacrum provides strength and stability to the pelvis and transmits body weight to the pelvic girdle through the sacroiliac joints.

The base of the sacrum is formed by the superior surface of the S1 vertebra. Its superior articular processes articulate with the inferior articular processes of the L5 vertebra.

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The projecting anterior edge of the body of the first sacral vertebra is the sacral promontory.

On the pelvic and dorsal surfaces are four pairs of sacral foramina for the exit of the rami of the first four sacral nerves and the accompanying vessels.

The fused articular processes form the intermediate sacral crests, and the fused tips of the transverse processes form the lateral sacral crests.