Neuron cell bodies are found primarily in which region of the central nervous system?

• A. gray matter of the CNS
• B. white matter of the CNS
• C. Cerebrospinal fluid
• D. Nerve tracts

Answer: (A)

Neuron cell bodies are located where the tissue is referred to as gray matter. This region contains the cell bodies themselves, their dendrites, synapses, and much of the neuropil, all of which give it a darker appearance on H&E stains. In the CNS, gray matter forms the cerebral cortex and deep nuclei in the brain, and the dorsal and ventral horns of the spinal cord, where neuron cell bodies reside and communicate locally.

White matter, in contrast, is made up mostly of myelinated axons forming tracts that connect different brain regions and spinal segments. Myelin is lipid-rich and bright, giving white matter its lighter color and its role as the communication highways of the CNS, with relatively few neuronal cell bodies present there.

Cerebrospinal fluid is a circulating fluid, not a tissue component containing neuron cell bodies, and nerve tracts are bundles of axons within white matter, not clusters of neuron cell bodies. Therefore, the region housing neuron cell bodies is the gray matter of the CNS.