The spinal cord runs from the brain down the back inside the protective vertebral column. It is made up of the very long, thin axons (nerve fibers) of thousands of nerve cells bringing their messages to and from the brain and body. It is also the site of spinal reflexes starting and ending in the spinal cord with no input from the brain.
The 31 pairs of spinal nerves coming off the spinal cord are each made up of thousands of nerve fibers. These are all mixed nerves (both receiving and send sending signals), connected to the spinal cord by two roots – the doral root and ventral root. Each root is made up of rootlets that attach along that segment of the spinal cord which that spinal nerve serves.
The ventral root (anterior in the cord) contains the motor (efferent) messages coming out of the spinal cord. These fibers come off the anterior horn of the spinal cord gray matter, where motor neurons innervate the skeletal muscles.
The dorsal root (posterior side of the cord) contains the sensory (afferent) fibers coming into the spinal cord from sensory neurons in the dorsal root ganglia. They are bringing in sensory impulses from receptors in the body.
