Explain the Spinal Nerves

As mentioned earlier, there are 31 pairs of spinal nerves that leave the vertebral canal by passing through the intervertebral foramina formed by adjacent vertebrae. All of the spinal nerves are "mixed", that is, they contain both sensory and motor neurons. A representation of these spinal nerves supplying to the specific organs, you may recall has already been presented, in Figure. Look up Figure now. You will realize that these spinal nerves are named and grouped according to vertebrae to which they are associated.

8 - Cervical, 12 - Thoracic, 5 - Lumbal, 5 - Sacral, 1 - Coccygeal

Although there are only 7 cervical vertebrae, there are eight nerves because the first pair leaves the vertebral canal between the occipital bone and the atlas and eighth pair leaves below last cervical vertebrae. Lumbar, sacral, coccygeal nerves leave spinal cord near its termination at the level of first lumbar vertebrae. They extend down inside the vertebral canal in the subarachnoid space, which forms a sheaf of nerves, which resembles a horse's tail - the cauda equina. They leave the vertebral canal at the appropriate lumbar, sacral or coccygeal level. There are 12 pairs of thoracic nerve. Eleven of them are situated between the ribs, and are therefore termed intercostal; the twelfth lies below the last rib. They pass in-between the ribs supplying the intercostal muscles and overlying skin. The 12^th pairs are the sub costal nerves. The 7^th to 12^th thoracic nerves also supply muscles of the skin of posterior and anterior abdominal walls. The spinal nerve arises from both sides of spinal cord and emerges through intervertebral foramina. Each nerve is formed by the union of a motor and sensory nerve root and thus forms a mixed nerve, as mentioned above. Each spinal nerve has contributions from sympathetic part of autonomic nervous system in the form of a preganglionic fibre.