Question

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that

(A) the threshold value in the postsynaptic membrane is different for cell X and cell Y.

(B) the axon of cell X is myelinated, but that of cell Y is not.

(C) only cell Y produces an enzyme that terminates the activity of the neurotransmitter.

(D) cells X and Y express different receptor molecules for this particular neurotransmitter.

Short answer

(A) The statement“the threshold value in the postsynaptic membrane is different for cell X and cell Y” is false.

(B) The statement “the axon of cell X is myelinated, but that of cell Y is not” is false.

(C) The statement “only cell Y produces an enzyme that terminates the activity of the neurotransmitter” is false.

(D) The statement “cells X and Y express different receptor molecules for this particular neurotransmitter” is true.

Step-by-step solution

Neurotransmitter molecules

The term neurotransmitter is used to describechemical molecules of the nervous system that help propagate signals from one neuron end to another neuron or target organs. These molecules are commonly referred to as signaling molecules, and different neurons have different neurotransmitters.

Explanation of option ‘(A)’

The threshold value of a neuron denotes the minimum amount of electrical excitation required by the neuron to generate an action potential. It is only a set value and does not regulate the generation or inhibition of postsynaptic potential.

Thus, the difference in the threshold value of cell X and cell Y cannot influence the type of postsynaptic potential generated in these cells.

Therefore, the given statement is true.

Explanation of option ‘(B)’

In the nervous system, the myelination of axonal fibers provides insulation to the neuron structure and enhances the speed of signal conduction. The myelin sheath does not regulate the generation of EPSP (excitatory postsynaptic potential) or IPSP (inhibitory postsynaptic potential).

Thus, myelination does not determine the type of postsynaptic potential.

Therefore, the given statement is false.

Explanation of option ‘(C)’

If a postsynaptic cell produces an enzymatic molecule that degrades the neurotransmitter molecule, then the postsynaptic potential duration would decrease.

Thus,the release of an enzyme that terminates neurotransmitters cannot trigger the generation of EPSP in cell Y.

Therefore, the given statement is false.

Explanation of option ‘(D)’

A postsynaptic cell comprises receptor molecules for neurotransmitters, and a single neurotransmitter can link with more than one type of receptor. The type of receptor linked with the neurotransmitter influences the response generated by the neurotransmitter.

Some receptors facilitate the generation of IPSP (inhibitory postsynaptic potential), while some are known for generating EPSP from a single type of neurotransmitter.

Thus, the generation of EPSP in cell Y and IPSP in cell X from the same neurotransmitter can be due to the difference in receptors expressed by these cells.

Therefore, the given statement is true.