What is the mode of action of a toxin that binds specifically to the voltage-gated sodium channels of axons,?

Question

preventing these channels from opening?

a) block all sodium movement
b) block repolarization
c) prevent the axon from reaching the threshold potential
d) a and b only
e) a, b, and c

Answer 1

A would be correct. Tetrodotoxin is the most common example of a sodium channel blocker (found in puffer fish, which is a food delicacy in japan).

Repolarization is a result of potassium ions flowing out of the cell.

Threshold potential is created by membrane potentials from surrounding areas that stimulate action potentials (i.e. an action potential traveling along an axon).

Answer 2

I think it may be all. I'm not quite sure but I'll tell you my steps of thought. The sodium is needed to let the potassium flow through (switching the Na and the K), so I'm guessing it would block the sodium from flowing through anymore cause the toxin is stuck there, also allowing the potassium to flow through freely, which would stop it from repolarizing again, which obviously prevents it from repolarizing to the action potential and in effect keep it from recovering from the undershoot phase (aka reaching the threshold potential)