General physiology: chloride gradient in immature neurones: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · General physiology: chloride gradient in immature neurones

Sample item

In immature cortical neurones, high NKCC1 activity keeps intracellular chloride above its equilibrium level. What happens when GABA-A receptors open in these cells?

APotassium leaves the cell and the membrane hyperpolarisesBSodium enters through the GABA-A pore and the cell depolarisesCChloride enters the cell and the membrane hyperpolarisesDChloride leaves the cell and the membrane depolarises

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Chloride leaves the cell and the membrane depolarises

The direction of chloride flow depends on the chloride equilibrium potential. When NKCC1 loads the cell with chloride, ECl is less negative than the resting potential, so opening GABA-A channels lets chloride exit and depolarises the cell. In mature neurones KCC2 lowers intracellular chloride and GABA is hyperpolarising.

Option by option

A. Potassium leaves the cell and the membrane hyperpolarises
GABA-A channels do not pass potassium, so potassium efflux is not the mechanism.
B. Sodium enters through the GABA-A pore and the cell depolarises
The GABA-A channel is selective for anions, not sodium.
C. Chloride enters the cell and the membrane hyperpolarises
Chloride influx and hyperpolarisation is the mature pattern with KCC2 dominance.
D. Chloride leaves the cell and the membrane depolarises (correct)
Correct. With raised intracellular chloride the driving force favours efflux, which depolarises.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, Chloride leaves the cell and the membrane depolarises. The direction of chloride flow depends on the chloride equilibrium potential.

Why is "Potassium leaves the cell and the membrane hyperpolarises" not the answer?

GABA-A channels do not pass potassium, so potassium efflux is not the mechanism.

Why is "Sodium enters through the GABA-A pore and the cell depolarises" not the answer?

The GABA-A channel is selective for anions, not sodium.

Why is "Chloride enters the cell and the membrane hyperpolarises" not the answer?

Chloride influx and hyperpolarisation is the mature pattern with KCC2 dominance.

What concept does this question test?

It tests General physiology: chloride gradient in immature neurones in Physiology. When NKCC1 loads the cell with chloride, ECl is less negative than the resting potential, so opening GABA-A channels lets chloride exit and depolarises the cell. In mature neurones KCC2 lowers intracellular chloride and GABA is hyperpolarising.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study General physiology: chloride gradient in immature neurones?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.