THE HUMAN SPINAL CORD
Extending inferiorly from the brain is the spinal cord (Figure 12-6).
Figure 12-6. A cross section of the spinal cord.
a. The spinal cord is continuous with the brainstem. Together, the spinal cord
and the brainstem are called the neuraxis. The foramen magnum is taken as the point
that divides the brainstem from the spinal cord. Thus, the brainstem is within the cranial
cavity of the skull, and the spinal cord is within the vertebral (spinal) canal of the
b. The spinal cord has a central portion known as the gray matter. The gray
matter is surrounded by the white matter.
(1) The gray matter is made up of the cell bodies of many different kinds of
(2) The white matter is made up of the processes of neurons. The white
color is due to their myelin sheaths. These processes serve several purposes: Many
make a variety of connections within the spinal cord. Many ascend the neuraxis to carry
information to the brain. Many descend the neuraxis to carry commands from the brain.