Final answer:
The myelin sheath wraps around the axon of a neuron, providing insulation and facilitating the rapid transmission of electrical signals. Composed of layers from glial cells, it is comparable to electrical wire insulation, with gaps known as nodes of Ranvier for signal propagation.
Step-by-step explanation:
The myelin sheath (formed by neurolemmocytes) wraps around the axon of a neuron to provide protection and insulation. This lipid-rich layer, formed by oligodendrocytes in the CNS and Schwann cells in the PNS, facilitates the rapid transmission of electrical signals along the axon. The myelin sheath can be visualized as a pastry wrapping, much like in 'pigs in a blanket', that spirally encloses the axon with minimal cytoplasm between layers. Several layers of the glial cell membrane wrap around the axon, and include important proteins that help to maintain the integrity and close association of these layers.
During development, a glial cell wraps its membrane loosely around an axon segment. Eventually, the edges of this wrapping meet and one end tucks under the other, forming multiple insulating layers around the axon to create a complete enclosure. This structure is critical as it insulates the electrical signals that travel down the axon, much like the insulation on an electrical cord, preventing signal loss and increasing transmission speed. Interruptions in the myelin sheath, known as the nodes of Ranvier, occur at regular intervals and are essential for the 'recharging' of the signal as it propagates along the axon.