Question

what is the function of the myelin sheath?
the myelin sheath increases the insulation along the entire length of the axon.
the myelin sheath decreases the resistance of the axonal membrane to the flow of charge.
the myelin sheath decreases the speed of action potential conduction from the initial segment to the axon terminals.
the myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

Explanation:

The myelin sheath is a fatty layer that wraps around axons. It acts as an insulator. In non - myelinated axons, action potentials travel as continuous waves. In myelinated axons, due to the insulation provided by the myelin sheath, action potentials "jump" from one node of Ranvier (unmyelinated gaps) to the next. This is called saltatory conduction. Saltatory conduction significantly increases the speed of action potential conduction from the initial segment to the axon terminals.

• The first option is incorrect because the myelin sheath is not continuous along the entire axon (there are nodes of Ranvier).
• The second option is incorrect as the myelin sheath increases the resistance of the axonal membrane to the flow of charge (it is an insulator).
• The third option is incorrect because it does not decrease the speed but rather increases it.

Answer:

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.