nervous system p.2

THE NERVOUS SYSTEM 2
CNS
A. White matter and gray matter are both present in the CNS.
1. White matter contains mostly myelinated nerve fibers but also some unmyelinated fibers and neuroglial cells.
2. Gray matter contains neuronal cell bodies, many unmyelinated fibers, some myelinated fibers, and neuroglial cells.
3. Spinal cord gray matter appears in the shape of an H in cross-sections of the spinal cord.
a. A small central canal, lined by ependymal cells, is at the center of the crossbar in the H. This canal is a remnant of the embryonic neural tube.
b. The dorsal vertical bars of the H (dorsal horns) consist of sensory fibers extending from the dorsal root ganglia and cell bodies of interneurons.
c. The ventral vertical bars of the H (ventral horns) consist of cell bodies and fibers of large multipolar motor neurons.
4. Brain gray matter is located at the periphery (cortex) of the cerebrum and cerebellum. White matter lies beneath the gray matter in these structures.
a. The Purkinje cell layer (cerebellar cortex only) consists of flask-shaped Purkinje cells. These cells have a central nucleus, highly branched (arborized) dendrites, and a single myelinated