What structure surrounds the axons of nerve fibers and is formed by Schwann cells?

The myelin sheath is a crucial structure in the nervous system, formed by Schwann cells that envelop the axons of nerve fibers. This specialized layer provides insulation, which enhances the speed and efficiency of electrical signal transmission along the axon. Schwann cells wrap around the axon multiple times, creating this fatty insulating sheath that reduces ion leakage during action potentials.

The presence of the myelin sheath allows nerve impulses to travel more quickly compared to unmyelinated fibers, facilitating rapid communication between different parts of the nervous system. Moreover, the myelin sheath plays a significant role in maintaining the health of axons and supporting the overall function of neurons.

In contrast, demyelination refers to the loss of this myelin sheath, which can slow down or block nerve signals. The nodes of Ranvier are the gaps in the myelin sheath that allow for saltatory conduction, but they are not the structure itself that surrounds the axon. Neurolemma is a term that can refer specifically to the outermost layer of a Schwann cell and not the entire myelin sheath. This distinction emphasizes the importance of the myelin sheath in neuronal function and its role in promoting efficient signaling throughout the nervous system.