Question

A hypothetical postsynaptic neuron has three presynaptic inputs X, Y, and Z. When X and Y are stimulated simultaneously, the postsynaptic neuron undergoes an action potential, yet when X and Z are stimulated simultaneously, there is no change in the postsynaptic neuron's potential. What can you conclude?

Answer 1

The questions is incomplete, below is the complete question;

Assume a hypothetical postsynaptic neuron has three presynaptic inputs - X,Y,Z. When presynaptic neurons X and Z are stimulated simultaneously, the post synaptic neuron reaches threshold and undergoes an action potential, yet when presynpatic neuron X and Y are stimulated simultaneously, there is no change in potential of the post-synaptic neuron. What can you tell about presynaptic neurons X and Y?

a. presynaptic neurons X and Y are both inhibitory

b. presynaptic neuron X is inhibitory, and Y is excitatory

c. presynaptic neuron X is excitatory, and presynaptic neuron Y is inhibitory

d. only Y has an excitatory effect on the postsynaptic membrane

e. presynaptic neurons X and Y are both excitatory.

The correct answer to the question is option C

PRESYNAPTIC NEURONE X IS EXCITATORY AND PRESYNAPTIC NEURONE Y IS INHIBITORY.

Simply explained, presynaptic neurone X is said to be excitatory because when it is stimulated simultaneously alongside it's co-presynaptic neurone Z, it causes the post synaptic neurone to reach it's threshold and undergo an action potential but when presynaptic neurone X and Y are stimulated simultaneously,there is no change in the threshold of the postsynaptic neurone and no action potential is achieved.(that is presynaptic neurone Y inhibites the excitatory properties of presynaptic X)

An action potential is said to have occured when a neuron sends information down an axon, away from the cell body,It is caused by either threshold or suprathreshold stimuli that occurs upon a neuron. Action potential consists of four phases; hypopolarization, depolarization, overshoot, and repolarization.

An action potential propagates along the cell membrane of an axon until it reaches the terminal button.

Answer 2

a. presynaptic neuron Y and Z both are excitatory

b. Presynaptic neuron Y and Z are both inhibitory

c. presynpotic neuron Y is excitatory, Presynaptic neuron Z is inhibitory

d. presynaptic neuron Y is inhibitory, presynaptic Z is excitatory

Answer:

The correct answer is (c).Presynaptic Y is excitatory, while presynaptic Z is inhibitory

Step-by-step explanation:

Presynaptic neurons,as the name suggests is a neurons just before a synapse, i.e. located on the axon. They basically 'deliever' the neurotransmitters. While postsynaptic neurons are the neurons that are across the synapse(located on dendrite or soma). They are basically the 'receiver' of neurotransmitters.

When both presynatic X and Y were stimulated simultaneously, an action potential was generated at the postsynaptic neurone, which goes to show that both presynaptic X and Y are excitatory neurons. On the other hand, when presynaptic X and Z were stimulated simultaneously, no action potential was generated. Which means that one of them is inhibitory neuron. From previous information, we know that X is excitatory, which means that presynaptic Z is inhibitory neuron.

Therefore, option "c" is true.