For the following questions, assume a hypothetical postsynaptic neuron has three presynaptic inputs: neurons X, Y, and Z. Also, assume neuron Z is excitatory. If neurotransmitter from X causes a slight hyperpolarization of the postsynaptic cell, then the
A) synapse is excitatory
B) synapse is inhibitory
C) synapse could be excitatory or inhibitory
D) postsynaptic cell's membrane potential has decreased
E) synapse is excitatory and the postsynaptic cell's membrane potential has decreased

Question

Quizplus · Accepted Answer

A hyperpolarization of the postsynaptic cell means that the membrane potential is becoming more negative, which is inhibitory. Therefore, the synapse from neuron X is inhibitory. The fact that neuron Z is excitatory is not relevant to this particular synapse. The answer is not C, because a hyperpolarization is always inhibitory. While choice E is technically correct, it is not the best choice because it is more specific than necessary.

For the Following Questions, Assume a Hypothetical Postsynaptic Neuron Has