What is the primary function of myelin sheaths on axons?

• A. To nourish the nerve cell
• B. To provide structural support
• C. To speed up electrical transmission
• D. To increase neurotransmitter release

Answer: (C)

The primary function of myelin sheaths on axons is to speed up electrical transmission. Myelin is a fatty substance that wraps around the axons of many neurons, creating an insulating layer. This insulation allows electrical impulses to travel more swiftly along the axon by facilitating a process known as saltatory conduction. In this process, the action potential jumps from one node of Ranvier (the gaps in the myelin sheath) to another, significantly enhancing the speed of signal transmission compared to unmyelinated axons, where the impulse must travel continuously along the membrane.

The other functions mentioned, such as nourishing the nerve cell or providing structural support, are not the primary roles of myelin. While some forms of neuron support do involve glial cells that provide nourishment and structural integrity, myelin itself is specifically designed for increasing the conductivity of impulses along the axon. Additionally, neurotransmitter release is a distinct and separate process that occurs at the axon terminals and does not directly relate to the presence or function of myelin sheaths on the axons.