The correct answer is A. Schwann cells.
Schwann cells are associated with the peripheral nervous system (PNS) and not the central nervous system (CNS). They play a crucial role in supporting nerve regeneration, producing myelin for peripheral neurons, and providing insulation to axons in the PNS. The other options - Axon, Node of Ranvier, Myelin sheath, and Dendrite - are all structures or components that can be found in both the CNS and PNS.
