Multiple Choice
How does an action potential move deep into the muscle cell?
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11. Nervous Tissue and Nervous System
Propagation of Action Potentials
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In the context of propagation of action potentials, which type of neuron conducts impulses the fastest under normal physiological conditions?
A
A small-diameter, unmyelinated axon (e.g., a C fiber)
B
A large-diameter, myelinated axon (e.g., a somatic motor neuron)
C
A small-diameter, myelinated axon (e.g., a thin Aδ fiber)
D
A large-diameter, unmyelinated axon
Verified step by step guidance1
Step 1: Understand that the speed of action potential conduction depends primarily on two factors: axon diameter and myelination.
Step 2: Recall that larger diameter axons have less internal resistance to the flow of ions, which allows faster conduction of impulses.
Step 3: Recognize that myelination increases conduction speed by enabling saltatory conduction, where the action potential jumps between nodes of Ranvier.
Step 4: Compare the options: small-diameter unmyelinated axons conduct slowly, while large-diameter myelinated axons conduct quickly due to both factors favoring speed.
Step 5: Conclude that the fastest conduction occurs in large-diameter, myelinated axons, such as somatic motor neurons, because they combine both large diameter and myelination.
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