Which of the following does not contribute to propagation of action potentials? a) The refractory period...

Which of the following does not contribute to propagation of action potentials?

a) The refractory period allows the impulse to travel in only one direction.

b) Increasing the intensity of the stimulus increases the number of action potentials.

c) The magnitude of the action potential stays the same as it travels down the axon.

d) Each segment of the axon prevents the adjacent segments from firing.

e) As the area outside the membrane becomes negative, it attracts ions from adjacent regions; as the inside of the membrane becomes positive, it attracts negative ions from nearby in the cytoplasm. These events depolarize nearby regions of the axon membrane.

Expert Solution

The refractory period effectively allows the impulse to travel in only one direction, since it prevents the stimulated zones to be stimulated again, since the resting potential has to be restored by the Na+/K+ ATPase. The magnitude stays the same, since depolarization of the membrane travels across all the length of the axon, and membrane depolarization in a zone of the axon allows the movement of charges to the nearby zones both outside and inside the cell, so the action potential can travel in one direction. Increasing the intensity of the stimulus. Increasing the intensity of the stimulus increases the number of action potentials until a certain frequency is reached since the action potentials are modulated frequency signals due to the refractory period in which voltage-gated Na+ channels are inactivated. However, each segment of the axon doesn't prevent the adjacent segments from firing, what prevents firing of stimulated zones is the refractory period as I said previously and depolarization in one segment of the axon promotes the depolarization of the adjacent non-stimulated zone, so the correct answer is D).

As you can see in this diagram, the red zone is hyperpolarized and the resting potential hasn't been restored by the Na+/K+ ATPase and voltage-gated Na+ channels are inactivated, so despite positive charges could travel there down its electrochemical gradient, no depolarization will occur. The depolarized zone shown in blue allows positive charge to travel to the zone that hasn't been stimulated (in white) down its electrochemical gradient, so voltage-gated Na+ channels are able to open in response to the depolarization of the previous region.

gladiator answered 2 years ago

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