Site of Action Potential

[663697]

Which of the following would most likely occur if an electrical stimulus were applied at point C in Figure 2?

A. An action potential would propogate toward point D.

B. An action potential would propagate toward point B.

C. No action potential would occur.

D. An action potential would propagate towards points B and D simultaneously. Correct Answer

Isn't the action potential supposed to travel in one direction from the soma to the terminal? And wouldn't it need to be initiated at the hillock in the first place for the action potential to fire?

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[desperadoflakes]

Well, that's how we usually think of it, but it's not necessarily what needs to happen. In a myelinated neuron, you don't really have any ligand-gated ion channels at the nodes of ranvier, so you won't be getting any EPSPs in the middle of the axon. But think about the mechanism of the action potential. When the membrane potential rises about -55mV, boom, action potential propagates. Sodium flows in, etc. etc. When it starts in the axon hillock we usually think of the ions flowing to the right, inducing depolarizations and action potentials down the axon. In actuality, the ions are flowing both ways. But when we start at the hillock and the action potential is flowing down, even tho ions are flowing in from the outside and going both ways, the voltage-gated channels in the direction from which the action potential are in their refractory periods, so they can't depolarize again.

But if we started from the middle, then no channels are in a refractory period, and the signal will propagate both ways. Interesting question.