- A Astrocytes, which regulate the blood-brain barrier
- B Schwann cells (in PNS) alone, with no CNS counterpart
- C Neurons themselves, by folding their own membrane
- D Oligodendrocytes (in CNS) or Schwann cells (in PNS)
Correct answer: D. Oligodendrocytes (in CNS) or Schwann cells (in PNS)
Explanation: Myelin sheath is formed by Schwann cells in the peripheral nervous system and by oligodendrocytes in the CNS. It speeds nerve impulses.
Concept context
Brain, spinal cord, neurons, reflex arcs, and sense organs.