Anatomy Practice Exam

Which part of the central nervous system does white matter primarily consist of?

1. Axons

2. Spinal fluid

3. Cell bodies

4. Dendrites

The correct answer is: Axons

White matter in the central nervous system primarily consists of axons. These axons are the long, slender projections of nerve cells (neurons) that transmit electrical signals across distances within the nervous system. The appearance of white matter is due to the myelin sheath that surrounds many of these axons, which is a fatty substance that enhances signal conduction and gives the matter its characteristic white color. In contrast, the other components mentioned—spinal fluid, cell bodies, and dendrites—play different roles. Spinal fluid surrounds and protects the brain and spinal cord, providing cushioning and serving as a medium for nutrient transport. Cell bodies of neurons contain the nucleus and are primarily found in gray matter, where neuronal connections and processing occur. Dendrites are the branching extensions of neurons that receive signals from other neurons but do not contribute significantly to the structure of white matter. Understanding that white matter is composed mainly of myelinated axons helps in grasping how communication occurs within the central nervous system and the overall organization of neural tissues.