Spinal Cord

The Spinal Cord – The spinal cord serves two functions in the human body:

1.It provides conduction pathways to and from the brain relaying sensory and motor impulses.

2. It contains numerous reflex centers which function in the generation of automatic responses to incoming stimuli (reflexes). The reflex center is the central portion of a reflex arc and it may or may not contain interneurons.

The spinal cord extends from the foramen magnum where it merges with the medulla oblongata and extends to the second lumbar vertebra.

The spinal cord begins to taper past the 12th thoracic vertebra and ends at about the 2nd lumbar vertebra. After L2, the nerves of the spinal cord form a structure called the cauda equina, which means “horses tail.”

All along the length of the spinal cord 31 pairs of spinal nerves emerge. These consist of mixed nerves in the following numbers:

a. 8 pairs of cervical nerves.

b. 12 pairs of thoracic nerves.

c. 5 pairs of lumbar nerves.

d. 5 pairs of sacral nerves.

e. 1 pair of coccygeal nerves.

Impulses travel up and down conduction pathways in the spinal cord called tracts which are functionally associated bundles of nerve fibers. a. ascending tracts – these run impulses from the peripheral sensory nerve inputs to the brain. b. descending tracts – these run impulses from the brain to motor nerve outlets in the spinal cord.

So, overall, the spinal cord is a relay station for impulses traveling between the periphery and the brain and back to the periphery, as in reactions or as a relay station from the periphery directly back to the periphery, as in reflexes.