The Schwann cell forms a myelin sheath around which part of a peripheral nerve cell?

Introduction / Context:
This question tests your understanding of the structure of peripheral nerves and the role of Schwann cells. Myelination greatly influences the speed and efficiency of nerve impulse conduction. Knowing which part of the neuron is wrapped by Schwann cells helps clarify how action potentials travel along nerve fibers.

Given Data / Assumptions:

• We are dealing with neurons in the peripheral nervous system.
• Schwann cells are glial cells associated with these neurons.
• The options include nodes of Ranvier, dendrites, nucleus, and axon.
• We assume normal, myelinated peripheral nerve fibers.

Concept / Approach:
In the peripheral nervous system, Schwann cells wrap around the axons of neurons to form a multilayered myelin sheath. This myelin sheath insulates the axon and allows saltatory conduction, where action potentials jump from one node of Ranvier to the next. The nodes of Ranvier are gaps between adjacent myelin segments, not the structures that are directly wrapped. Dendrites receive signals, and the nucleus is part of the cell body. By recalling this anatomical arrangement, we can choose the correct answer.

Step-by-Step Solution:
Step 1: Recall that a typical neuron has dendrites, a cell body with a nucleus, and a long axon that carries nerve impulses away from the cell body.Step 2: In the peripheral nervous system, Schwann cells wrap their membranes around the axon many times to form the myelin sheath.Step 3: The node of Ranvier is a small gap between adjacent Schwann cells where the axon membrane is exposed and ion channels are concentrated.Step 4: Dendrites are usually not myelinated and primarily function to receive signals.Step 5: Therefore, the Schwann cell forms a myelin sheath around the axon of a peripheral neuron.

Verification / Alternative check:
In diagrams of myelinated neurons, you can visualize a series of Schwann cells like beads on a string, each wrapping a section of the axon. The nodes of Ranvier are the uncovered gaps between these cells. Remembering that the axon is the long projection carrying impulses makes it logical that myelin would insulate this conducting structure.

Why Other Options Are Wrong:
Nodes of Ranvier: These are gaps between myelin segments, so they are not the parts that the Schwann cells wrap; they are spaces between wrapped sections.
Dendrites: These shorter branching structures are usually not myelinated and mainly receive incoming signals rather than conduct signals over long distances.
Nucleus: The nucleus is housed in the cell body and is not surrounded by Schwann cell myelin in peripheral neurons.

Common Pitfalls:
Students sometimes confuse Schwann cells with oligodendrocytes, which myelinate axons in the central nervous system. Another pitfall is thinking that all parts of the neuron are equally myelinated. In reality, myelin concentrates on long axons, especially those that must conduct impulses quickly over distance.

Final Answer:
The Schwann cell forms a myelin sheath around the Axon of a peripheral nerve cell.