Vertebral Column: Structure and Function

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Vertebral Column: Structure and Function

Human Anatomy and Physiology

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Structural organization and functions of vertebral column

Objectives

Explain vertebral column curvatures
Describe structure and function of vertebrae

Vertebral column

Figure1: Parts of A Typical Vertebra

The Vertebral Column(1)

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

The typical vertebrae consists of

Body, transverse process, the foramen transversarium, the vertebral foramen and spinous process 6

The Vertebral Column(2)

The vertebral column (spine), extending from the cranium (skull) to the apex of the coccyx.

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.
Significant motion occurs between only the superior 25 vertebrae

The Vertebral Column(3)

The 5 sacral vertebrae are fused in adults to form the sacrum, and the 4 coccygeal vertebrae are fused to form the coccyx 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 8

Curvatures of Vertebral Column(1)

Curvatures of Vertebral Column(2)

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.

The thoracic and sacral (pelvic) curvatures (kyphoses) are concave anteriorly, whereas the cervical and lumbar curvatures (lordoses) are concave posteriorly.

Curvatures of Vertebral Column(3)

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

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.

Curvatures of Vertebral Column(4)

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 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.

Curvatures of Vertebral Column(5)

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 14

Structure of intervertebral Disc(1)

The intervertebral discs are the main structures that bind together the vertebral bodies, and they extend from C2 to the sacrum (C1 has no vertebral body) The discs are responsible for one quarter of the length of the vertebral column below the level of C2 They are thickest in the cervical and lumbar regions, where the movements of the vertebral column are greatest They may be regarded as semielastic discs, which lie between the rigid bodies of adjacent vertebrae Their physical characteristics permit them to serve as shock absorbers when the load on the vertebral column is suddenly increased, as when one is jumping from a height.

Structure of intervertebral Disc(2)

Their elasticity allows the rigid vertebrae to move one on the other

Unfortunately, their resilience is gradually lost with advancing age Each disc consists of a peripheral part, the anulus fibrosus, and a central part, the nucleus pulposus The anulus fibrosus is composed of fibrocartilage, in which the collagen fibers are arranged in concentric layers or sheets The nucleus pulposus in children and adolescents is an ovoid mass of gelatinous material containing a large amount of water, a small number of collagen fibers, and a few cartilage cells.

It is normally under pressure and situated slightly nearer to the posterior than to the anterior margin of the disc 16

Structure of intervertebral Disc(3)

No discs are found between the first two cervical vertebrae or in the sacrum or coccyx

Function of the intervertebral Disc(1)

The semifluid nature of the nucleus pulposus allows it to change shape and permits one vertebra to rock anteriorly or posteriorly on another, as in flexion and extension of the vertebral column A sudden increase in the compression load on the vertebral column causes the semifluid nucleus pulposus to become flattened.

The outward thrust of the nucleus is accommodated by the resilience of the surrounding annulus fibrosus Sometimes, the outward thrust is too great for the anulus fibrosus and it ruptures, allowing the nucleus pulposus to herniate and protrude into the vertebral canal, where it may press on the spinal nerve roots, the spinal nerve, or even the spinal cord 18

Function of the intervertebral Disc(2)

With advancing age, the water content of the nucleus pulposus diminishes and is replaced by fibrocartilage The collagen fibers of the anulus degenerate and, as a result, the anulus cannot always contain the nucleus pulposus under stress In old age, the discs are thin and less elastic, and it is no longer possible to distinguish the nucleus from the anulus.

Structure of Vertebrae(1)

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

Structure of Vertebrae(2)

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 21

Structure of Vertebrae(3)

In life, most of the superior and inferior surfaces of vertebral bodies are covered with hyaline cartilage, 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.

Structure of Vertebrae(4)

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 23

Structure of Vertebrae(5)

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

Structure of Vertebrae(6)

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(1)

One median spinous process projects posteriorly from the vertebral arch at the junction of the laminae and typically overlaps the vertebra below.

Two transverse processes project posterolaterally from the junctions of the pedicles and laminae.

Four articular processes two superior and two inferior also arise from the junctions of the pedicles and laminae, each bearing an articular surface (facet).

Seven Processes Arise From the Vertebral Arch of a Typical Vertebra(2)

The direction of the articular facets on the articular processes determines the types of movements permitted and restricted between the adjacent vertebrae of each region.

The interlocking of the articular processes also assists in keeping adjacent vertebrae aligned, particularly preventing one vertebra from slipping anteriorly on the vertebra below.

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 28

Characteristics of typical cervical vertebrae(1)

Body:

Small and wider from side to side than anteroposteriorly; superior surface is concave; inferior surface is convex 29

Characteristics of typical cervical vertebrae(2)

Vertebral foramen:
Large and triangular

Transverse processe:

Transverse foramina (L. foramina transversarium); small or absent in C7; vertebral arteries and accompanying venous and sympathetic plexuses pass through foramina (except C7, which transmits only small accessory vertebral veins); anterior and posterior tubercles 30

Characteristics of typical cervical vertebrae(3)

Articular processes:
Superior facets directed superoposteriorly; inferior facets directed inferoanteriorly

Spinous process:

C3C5 short and bifid (split in two parts); process of C6 is long but that of C7 is longer (C7 is called vertebra prominens) 31

Characteristics of the atypical cervical Vertebrae (1)

The 1st, 2nd, and 7th cervical vertebrae are atypical
The 1st cervical vertebra, or atlas , does not possess a body or a spinous process.

It has an anterior and posterior arch.

It has a lateral mass on each side with articular surfaces on its upper surface for articulation with the occipital condyles (atlanto-occipital joints) and articular surfaces on its inferior surface for articulation with the axis(atlantoaxial joints).

Characteristics of the atypical cervical Vertebrae (2)

The 2nd cervical vertebra, or axis, has a peglike odontoid process (dens) that projects from the superior surface of the body 33

Characteristics of the atypical cervical Vertebrae (3)

The 7th cervical vertebra, or vertebra prominens, is so named because it has the longest spinous process, and the process is not bifid.

The transverse process is large, but the foramen transversarium is small and transmits the vertebral vein or veins.

Characteristics of Thoracic Vertebrae(1)

Body:
Heart-shaped; has one or two facets for articulation with head of rib (H)
Vertebral foramen:
Circular and smaller than those in cervical and lumbar regions

Characteristics of Thoracic Vertebrae(2)

Transverse process (TP)
Long and strong; extends posterolaterally; length diminishes from T1 to T12

Characteristics of Thoracic Vertebrae(2)

Articular processes:

Superior facets directed posteriorly and slightly laterally; inferior facets directed anteriorly and slightly medially Spinous process (SP)

Long; slopes poster inferiorly; tip extends to level of vertebral body below

Characteristics of lumbar Vertebrae

Body
Massive; kidney-shaped when viewed
Vertebral foramen
Triangular
Transverse processes
Long and slender
Articular processes
Superior facets directed

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 40

Sacrum and Cocygeal Vertebrae

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.

Key Points

There are 33 vertebrae 7 cervical vertebrae, 12 thoracic vertebrae, 5 Lumber vertebrae, 5 sacral vertebrae and 4 coccyx A typical vertebrae consists of body, transverse process, the foramen transversarium, the vertebral foramen and spinous process.

Evaluation

Describe the structure of vertebral column.
What are the functions of the vertebral column?