Myelinated fibers (tracts) form ________ matter while unmyelinated fibers form ________ matter.

• A. white; gray
• B. yellow; red
• C. gray; white
• D. red; yellow

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the structure of the nervous system. Myelinated fibers are axons covered by a fatty substance called myelin, which insulates the axon and speeds up the transmission of nerve impulses. Unmyelinated fibers lack this myelin sheath.
2. Step 2: Learn the distinction between white matter and gray matter. White matter primarily consists of myelinated axons, which give it a lighter appearance due to the presence of myelin. Gray matter, on the other hand, is composed of unmyelinated fibers, cell bodies, dendrites, and synapses, giving it a darker appearance.
3. Step 3: Relate the terms 'myelinated' and 'unmyelinated' to the corresponding types of matter. Myelinated fibers form white matter, while unmyelinated fibers form gray matter.
4. Step 4: Review the options provided in the question. The correct pairing is 'white; gray,' as it matches the anatomical and physiological characteristics of myelinated and unmyelinated fibers.
5. Step 5: Eliminate incorrect options such as 'yellow; red,' 'gray; white,' and 'red; yellow,' as they do not accurately describe the relationship between myelinated/unmyelinated fibers and white/gray matter.