National League for Nursing (NLN PAX) Practice Exam

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What is the primary function of the myelin sheath surrounding many neurons?

  1. Protect the neuron

  2. Increase the rate of impulse transport

  3. Store neurotransmitters

  4. Facilitate hormone transport

The correct answer is: Increase the rate of impulse transport

The primary function of the myelin sheath surrounding many neurons is to increase the rate of impulse transport. The myelin sheath is a fatty layer that wraps around the axons of neurons, providing insulation. This insulation allows electrical impulses, known as action potentials, to travel more quickly along the neuron. The process whereby impulses jump from one node of Ranvier (unmyelinated gaps in the sheath) to another in a process called saltatory conduction significantly enhances the speed of transmission compared to unmyelinated fibers. The other options, while related to neuronal function, do not accurately reflect the primary role of the myelin sheath. Protecting the neuron is a more general function that can stem from various aspects of the neuron's structure and environment rather than specifically from the myelin sheath itself. Storing neurotransmitters is a function of synaptic vesicles located at the axon terminals, not of the myelin sheath. Facilitating hormone transport is more relevant to the endocrine system rather than the nervous system, where myelin is found, further clarifying the unique role the myelin sheath plays in neuronal impulse conduction.