General physiology: inhibitory synapse: 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: inhibitory synapse

Sample item

A patient in status epilepticus is given intravenous lorazepam. Which postsynaptic event mediates its inhibitory effect?

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

The answer and the reasoning

A. Greater Cl- influx through GABA-A receptors, which hyperpolarises the neurone

Benzodiazepines bind the GABA-A receptor and increase the frequency of Cl- channel opening in the presence of GABA. Cl- entry produces an inhibitory postsynaptic potential, hyperpolarising the cell and moving it away from threshold. Barbiturates act on the same channel but prolong its opening.

Option by option

  • A. Greater Cl- influx through GABA-A receptors, which hyperpolarises the neurone (correct)

    Enhanced chloride entry through the ionotropic GABA-A receptor produces fast inhibition.

  • B. Blockade of NMDA-type glutamate receptors

    NMDA receptor blockade is the mechanism of ketamine and memantine.

  • C. Greater K+ efflux through GABA-B receptor-coupled channels

    GABA-B receptors are metabotropic and are the target of baclofen, not benzodiazepines.

  • D. Blockade of voltage-gated Na+ channels in the axon

    Sodium channel blockade is the mechanism of phenytoin and carbamazepine.

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.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is A, Greater Cl- influx through GABA-A receptors, which hyperpolarises the neurone. Benzodiazepines bind the GABA-A receptor and increase the frequency of Cl- channel opening in the presence of GABA.

Why is "Blockade of NMDA-type glutamate receptors" not the answer?

NMDA receptor blockade is the mechanism of ketamine and memantine.

Why is "Greater K+ efflux through GABA-B receptor-coupled channels" not the answer?

GABA-B receptors are metabotropic and are the target of baclofen, not benzodiazepines.

Why is "Blockade of voltage-gated Na+ channels in the axon" not the answer?

Sodium channel blockade is the mechanism of phenytoin and carbamazepine.

What concept does this question test?

It tests General physiology: inhibitory synapse in Physiology. Cl- entry produces an inhibitory postsynaptic potential, hyperpolarising the cell and moving it away from threshold. Barbiturates act on the same channel but prolong its opening.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: inhibitory synapse?

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.