Vertebrae25
5.2 Intervertebral discs25
5.3 Typical vertebra26
5.4 Regional variations in vertebrae26
5.5 Joints, ligaments and movements27
5.6 Arteries and veins of the vertebral column28
The vertebral column provides support. Flexibility is provided by its arrangement into individual vertebrae: 7 cervical, 12 thoracic, 5 lumbar and 5 fused to form the sacrum. Vertebrae are separated by intervertebral discs. Ligaments pass between equivalent parts of adjacent vertebrae to form a ligamentous and bony tube containing the spinal cord. Movements of the column are constrained by the anatomy of individual regions of the column and the rib cage. The venous plexuses around the column and inside the vertebral canal are important in the spread of disease, particularly from the lower abdomen and pelvis.
You should:
• list the bones that make up the vertebral column
• describe how the characteristics of vertebrae of the four main regions reflect function
• describe the function and disposition of intervertebral discs
• describe the main movements of the column and the muscles that produce them
• describe how the column is supplied with blood, and how its veins are important in the spread of disease.
5.1. Vertebrae
The vertebral column confers rigidity on the trunk: it is an adaptation to deal with gravity. A solid, rigid column would confer maximum rigidity, but then movement would be virtually impossible, so the column is broken up into individual vertebrae as follows:
• 7 cervical
• 12 thoracic (sometimes called dorsal, but this is misleading since they are no more dorsal than the others)
• 5 lumbar
• 5 sacral, fused into one bone, the sacrum
• a few coccygeal, which are very small and may be fused; forget about them.
5.2. Intervertebral discs
Intervertebral discs are found between all vertebrae from C2 to S1. They consist of:
• an annulus fibrosus: tough hyaline cartilaginous rim, and
• a nucleus pulposus: fibrocartilaginous core, softer, probably derived from remnants of the notochord.
Rupture of the annulus fibrosus may allow the softer nucleus pulposus to herniate and this may compress the spinal cord or segmental nerve roots in the spinal (vertebral) canal of the vertebral column. This is often somewhat inaccurately referred to as a slipped disc. The symptoms of this condition will depend upon at which level it occurs and which structures are affected. The herniation usually occurs to one side or the other, compressing nerve roots that leave the spinal (vertebral) canal below the site of herniation. If the herniation occurs in the midline, then the centrally situated nerve roots of the cauda equina may be affected, causing cauda equina syndrome. See Ch. 6, p. 31; Ch. 11, p. 151).
There is no disc between the base of the skull and vertebra C1 or between vertebrae C1 and C2; this is because of the specialised movements which take place here (see Ch. 14, p. 243).
