Which of the following structures is associated with unmyelinated axons in the peripheral nervous system (PNS)?

• A. Schwann cell cytoplasm enveloping multiple axons
• B. Myelin sheath
• C. Oligodendrocyte processes
• D. Nodes of Ranvier

Answer: (A)

Verified step by step guidance

1. Understand the context: Axons in the peripheral nervous system (PNS) can be either myelinated or unmyelinated. Myelinated axons are wrapped in a myelin sheath, which speeds up nerve impulse conduction, while unmyelinated axons are not surrounded by this sheath but are still supported by Schwann cells.
2. Recall the role of Schwann cells: Schwann cells are glial cells in the PNS responsible for supporting both myelinated and unmyelinated axons. For unmyelinated axons, Schwann cells provide structural and metabolic support by enveloping multiple axons within their cytoplasm.
3. Eliminate incorrect options: The 'myelin sheath' is associated with myelinated axons, not unmyelinated axons. 'Oligodendrocyte processes' are found in the central nervous system (CNS), not the PNS. 'Nodes of Ranvier' are gaps in the myelin sheath of myelinated axons, so they are not relevant to unmyelinated axons.
4. Focus on the correct option: Schwann cell cytoplasm enveloping multiple axons is the structure associated with unmyelinated axons in the PNS. This arrangement allows Schwann cells to support several unmyelinated axons simultaneously without forming a myelin sheath.
5. Summarize the concept: In the PNS, unmyelinated axons are supported by Schwann cells, which envelop multiple axons within their cytoplasm. This is distinct from the CNS, where oligodendrocytes are responsible for myelination and support.