Final answer:
Myelin is a lipid-rich sheath that is formed by oligodendrocytes in the CNS and Schwann cells in the PNS, which insulates axons to enhance electrical impulse transmission.
Step-by-step explanation:
Myelin is formed by oligodendrocytes and Schwann cells. Oligodendrocytes are responsible for producing the myelin sheaths in the central nervous system (CNS), which includes the brain and spinal cord. One oligodendrocyte can provide the myelin for multiple axon segments, either on the same neuron or on different neurons.
On the other hand, Schwann cells produce the myelin sheaths for axons in the peripheral nervous system (PNS). The myelin sheath is a lipid-rich layer that encapsulates the axon, enhancing the transmission of electrical impulses along the neuron. This insulation effect is crucial for the efficient functioning of the nervous system.