What term describes the myelinated nerve fiber tracts responsible for conduction within the brain and spinal cord?

• A. Gray matter
• B. White matter
• C. Blood-brain barrier
• D. Dural folds

Answer: (B)

White matter describes the networks of myelinated axons that carry signals quickly across the brain and down the spinal cord. Myelin wraps these axons, enabling saltatory conduction that speeds up transmission. These tracts connect gray matter regions and come in different types: association fibers linking nearby cortical areas, commissural fibers crossing between hemispheres (like in the corpus callosum), and projection fibers connecting the cortex with brainstem and spinal cord. In the brain, white matter lies beneath the cortex; in the spinal cord, it surrounds the gray matter and contains the ascending and descending pathways. The other options don’t fit because gray matter consists mainly of neuron cell bodies and unmyelinated processes, the blood-brain barrier is a protective capillary interface—not conducting tracts, and dural folds are ridges of the dura mater in the meninges.