(1) Enlargements. The spinal cord has two enlargements. One is the
cervical enlargement, associated with nerves for the upper members. The other is the
lumbosacral enlargement, associated with nerves for the lower members.
(2) Spinal nerves. A nerve is a bundle of neuron branches that carry
impulses to and from the CNS. Those nerves arising from the spinal cord are spinal
nerves. There are 31 pairs of spinal nerves.
b. A Cross Section of the Spinal Cord (Figure 5-7). The spinal cord is a
continuous structure that runs through the vertebral canal down to the lumbar region of
the column. It is composed of a mass of a central gray matter (cell bodies of neurons)
surrounded by peripheral white matter (myelinated branches of neurons). The gray and
white matter are thus considered columns of material. However, in cross section, this
effect of columns is lost.
Figure 5-7. A cross section of the spinal cord.