What are the main anatomical regions of the spine?
The spine is made up of a large number of spinal bones (vertebrae)
linked together by intervertebral discs and facet joints.
The human spine is divided into the cervical (highest), thoracic,
lumbar, sacral, and coccygeal (lowest) regions.
The vertebrae (spinal bones) in each region are numbered according
to their region (letter C, T, L or S) and location (number).
What are the intervertebral discs?
The intervertebral discs are soft structures which act as shock
absorbers between each of the vertebrae (bones) in the spine.
A single disc sits between each vertebra. Each intervertebral
disc has a strong outer ring of fibres (‘annulus’),
and a soft, jelly-like centre (nucleus).
The central soft and juicy nucleus is a spherical structure that
acts allows
tilting, rotating, and gliding movements in the spine. The nucleus
also serves as the main shock absorber. It is a transparent, gelatinous
substance that contains 88 percent water in young adults. With
age and/or degeneration, the water content drops significantly.
Collagen fibers, connective tissue cells, and a small amount of
cartilage compose the remainder of the nucleus. The nucleus does
not contain any blood vessels or nerves.
The annulus is the toughest part of the disc, and connects each
vertebral bone. The annulus is a ring-like mass of fibers enclose
the central nucleus and hold it under pressure to prevent rupture.
What are the laminae?
The laminae are ‘shingles’ of bone lying over the back
of the spinal canal. They meet in the midline, giving rise to the
spinous process. They are often removed (laminectomy) to decompress
the nerves in the spinal canal.
What are the facet joints?
The facet joints are small joints on each side at the back of the
spine which allow movement between adjacent vertebrae whilst
maintaining spinal stability. They form part of the roof of the
spinal canal, and the region of the spinal canal immediately
underneath the facet joint is known as the subarticular compartment
or lateral recess. Spinal nerves run through these compartments.
Where do the spinal nerves run?
The spinal canal and intervertebral foraminae in the lumbar spine
(lower back) are bony tunnels through which the spinal nerves
(nerve roots) run.
When the size of these tunnels is reduced, there is less room
for the spinal nerves, the consequence of which may be pressure
on these structures.
What about the spinal cord?
The spinal cord ends in the upper lumbar spine (usually at L1).
The lower portion of the spinal cord is known as the ‘conus’ or ‘conus
medullaris’. Pressure on the conus may cause impaired bowel
and bladder control, and numbness around the anus and genitals
(‘saddle anaesthesia’).
Below the ending of the spinal cord, the canal is occupied by
the spinal nerves (also known as the ‘cauda equina’ which
means ‘horses tail’, named after its appearance). These
nerves run through the canal and then out through their respective
intervertebral foraminae. These nerves supply function to the bladder,
bowels, genitals, and legs. |
