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Anatomy of Back Pain
The Somatic Nervous System |
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The somatic nervous system comprises:
- Sensory neurons that convey information from the head, body wall and limbs, and from
special receptors (for vision, hearing, taste and smell), to the central nervous system.
All of these sensations are consciously perceived.
- Motor neurons that conduct impulses from the CNS to the skeletal muscles only
– these can be consciously controlled, allowing for voluntary movement.
Given that there are muscles all over the body (literally from head to toe), somatic
spinal nerves can be found at virtually all spinal levels (C1-Co1). The exit point and
function of each nerve, however, is different – for example, the nerves which control
the neck muscles exit from vertebrae C1-C3, whereas the nerves that control the fingers
exit from C7-C8. |
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The diagram (opposite) maps the exit
points of the main, somatic, spinal nerves to the different parts of the body.
Compression of the facet joints in the neck (C1-C7) and/or back (T1-S1) will almost
certainly lead to back pain (conveyed by the sensory neurons).
However, given that the somatic nerves are mixed (that is, they contain both sensory and
motor neurons), compression might also lead to motor dysfunction of the skeletal muscles.
For example, compression of the joints from C1-T1 may result in one or more forms of palsy
(muscle paralysis) in the arms or shoulders, whereas compression from L1-S1 can result in
problems with the abdominal wall and/or lower limbs. |
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Referred Pain
Referred pain is also fairly common – this occurs when
the brain (which receives and interprets pain signals) is unable to identify the exact
location of the problem. The most common form of referred pain is probably sciatica a condition which occurs
when the sciatic nerve (part of the somatic system) is compressed. |
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The nerve itself has five roots on either
side of the spine – these roots exit the vertebral column from the foramina of L4-S3
(five holes = five roots) and come together to form the sciatic nerve – just below,
and to the side, of S4.
Compression of the articular facet joints at L4, L5 or S1 (that is, the boundaries of
L4-L3, L5-L4, or S1-L5) will lead to sciatic, nerve root impingement and hence to pain. |
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However, the brain finds it difficult to determine
whether the pain is coming from the nerve root, or from the main segment that extends into
the leg – as a result, the pain is sometimes perceived as originating in the
foot, leg or buttocks – a condition referred to as sciatica.
Next >>> The Autonomic Nervous System
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