The central nervous system is made up of the brain and spinal cord. The brain is explained and another article (click here). The spinal cord is the Grand Central Station of the motor, sensory, and autonomic nerves of the body. The spinal cord is enclosed within the vertebral column and is surrounded by a protective membrane called the meninges. Within the meninges the spinal cord is bathed with clear fluid called cerebral spinal fluid (CSF). The spinal cord extends from the foramen magnum, the large hole at the base of the skull, to the mid-lower back. A cross section of the spinal cord reveals the internal gray matter in the shape of a butterfly surrounded by the white matter. The gray matter is composed of that cell bodies and unmyelinated nerve parts. The white matter contains a high proportion of myelinated nerve fibers. It is the Schwan cells of the myelin sheaths that gives white matter its lighter color. The spinal cord itself contains vertical tracks comprised of neurons with certain functions. This is somewhat like different lanes in a highway. Ascending tracts contain sensory neurons that deliver impulses to the brain. The descending tracts carry motor impulses away from the brain.
There are 31 sets of nerves that arise from the spinal cord and project through the spaces between the vertebrae. These nerves are named based on the vertebrae from which they traverse. For example the first set of cervical spinal nerves are called "C1." Each spinal nerve has two roots, one traveling away from the spinal column (the ventral root) and one towards the spinal column (the dorsal root). Imagine the entrance and exit ramps from a highway. These would represent the dorsal and ventral roots, respectively. The dorsal root has a small knob close to the spinal cord that contains of the excel bodies of the sensory neurons.The ventral root contains the motor neurons. The cell bodies of the motor neurons are located within the gray matter of the spinal cord.
The cervical spinal nerves arise from the spaces between the cervical vertebrae. These nerves send signals to and from the head, neck, shoulders, arms, the upper back, and the diaphragm (the breathing muscle). "C3, C4, and C5 keep the diaphragm alive" is a phrase that helps medical students remember the function of these nerves.
The thoracic spinal nerves communicate with the torso.
The lumbar and sacral spinal nerves service the hips, pelvis, and legs.
Cauda equina Is a term derived from Latin for "horse's tail." At the level of approximately L1, the spinal cord splits into multiple nerves that dangle into the lower part of the spinal column. These nerves have the appearance of a horses tail - thus the name.
Last Updated (Saturday, 11 September 2010 11:26)