A postsynaptic neuron has three presynaptic inputs-from neurons X,Y,and Z.Stimulation of neuron X causes the postsynaptic neuron to depolarize by 0.5 mV. When X and Y are stimulated simultaneously,the postsynaptic neuron depolarizes by 1 mV. When X and Z are stimulated simultaneously,however,there is no change in the membrane potential of the postsynaptic neuron.What is most likely true about presynaptic neurons Y and Z?
A)They are both excitatory.
B)They are both inhibitory.
C)Y is excitatory and Z is inhibitory.
D)Z is excitatory and Y is inhibitory.

Question

A postsynaptic neuron has three presynaptic inputs-from neurons X,Y,and Z.Stimulation of neuron X causes the postsynaptic neuron to depolarize by 0.5 mV. When X and Y are stimulated simultaneously,the postsynaptic neuron depolarizes by 1 mV. When X and Z are stimulated simultaneously,however,there is no change in the membrane potential of the postsynaptic neuron.What is most likely true about presynaptic neurons Y and Z?
A)They are both excitatory.
B)They are both inhibitory.
C)Y is excitatory and Z is inhibitory.
D)Z is excitatory and Y is inhibitory.

Quizplus · Accepted Answer

When neuron X is stimulated, the postsynaptic neuron depolarizes, indicating that neuron X is excitatory. When neurons X and Y are stimulated together, the depolarization is twice as much as when neuron X alone is stimulated, indicating that neuron Y is also excitatory. When neurons X and Z are stimulated together, there is no change in the membrane potential of the postsynaptic neuron, indicating that neuron Z is inhibitory. Therefore, option C (Y is excitatory and Z is inhibitory) is the most likely scenario.

A Postsynaptic Neuron Has Three Presynaptic Inputs-From Neurons X,Y,and Z