Please help explain this biology problem to me...?

Question

This is a biology question I had on a past quiz. I got it wrong. I know what the correct answer is now, but I don't understand why it is right. Can someoen please help me? Here is the question:
If a motor neuron in the body were stimulated by an electrode placed about midpoint along the length of the axon_________. (Answer: D. the impulse would move to the axon terminal only.) The other choices were A. muscle contraction would occur. B. the impulse would spread bidirectionally. or C. the impluse would move to the axon terminal only, and the muscle contraction would occur. I chose A. I wasn't really sure of the answer, so I guessed. Can you help me understand why D is the correct answer? I appreciate your help! :)

Answer 1

That's a good question. The answer is D for a few reasons. Just because there is a pulse towards the axon, doesn't mean that there is enough of a potential to cause an action potential. Meaning that the neuron wouldn't fire and that muscle contraction wouldn't occur because it didn't get a signal from the neruon.

Remember for a neuron to fire it has to pass a certain threshold, and just because it got an impulse doesnt mean it passed threshold. One a neuron passes threshold (all or nothing) an action potential is generated, neurotransmitters are released , and the muscle would contract. Sometimes the signal may be too weak to push it passed threshold (0 mV or 0 V).

Hope this helps! Good luck!

Answer 2

Sounds like a neurology question to me. Biology is much different.