What structure is primarily responsible for wrapping around the axon to form the myelin sheath?

The myelin sheath is a crucial structure in the nervous system that insulates axons and enhances the speed of electrical signal transmission. Schwann cells are the primary cells responsible for the formation of the myelin sheath in the peripheral nervous system. These specialized glial cells wrap around the axons, creating multiple layers of cell membrane that act as an insulator.

This wrapping of Schwann cells around the axon not only provides insulation but also facilitates efficient nerve conduction through a process called saltatory conduction, where the electrical impulses jump between gaps in the myelin sheath known as the nodes of Ranvier. This increases the speed of signal transmission significantly compared to unmyelinated fibers.

The other choices refer to different parts of a neuron or related structures. Dendrites are responsible for receiving signals from other neurons, axon terminals transmit signals to other neurons or muscles, and the nodes of Ranvier are the gaps between myelinated sections where depolarization occurs during the conduction of impulses, but they do not form the myelin sheath themselves.