Assume a hypothetical postsynaptic neuron has three presynaptic inputs, X, Y, and Z. When presynaptic neurons X and Y are stimulated simultaneously, the postsynaptic neuron reaches threshold and undergoes an action potential; yet, when presynaptic neurons X and Z are stimulated simultaneously, there is no change in potential of the postsynaptic neuron. Which of these statements correctly describes the presynaptic neurons Y and Z?
A)Presynaptic neurons Y and Z are both excitatory.
B)Presynaptic neurons Y and Z are both inhibitory.
C) Presynaptic neuron Y is excitatory, and presynaptic neuron Z is inhibitory.
D) Presynaptic neuron Y is inhibitory, and presynaptic neuron Z is excitatory.

Question

Quizplus · Accepted Answer

When presynaptic neurons X and Y are stimulated simultaneously, the postsynaptic neuron reaches threshold and undergoes an action potential. This means presynaptic neuron Y is excitatory, contributing to the depolarization of the postsynaptic neuron. When presynaptic neurons X and Z are stimulated simultaneously, there is no change in potential of the postsynaptic neuron. This means presynaptic neuron Z is not contributing to the depolarization of the postsynaptic neuron and may be inhibitory. Therefore, the correct statement is "Presynaptic neuron Y is excitatory, and presynaptic neuron Z is inhibitory."

Assume a Hypothetical Postsynaptic Neuron Has Three Presynaptic Inputs, X