Special senses: vision: 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 · Special senses: vision

Sample item

What is the effect of light on the membrane of a rod photoreceptor?

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

The answer and the reasoning

D. Closure of cGMP-gated sodium channels with hyperpolarisation

Light isomerises retinal in rhodopsin, activating transducin and phosphodiesterase, which breaks down cGMP. The fall in cGMP closes cGMP-gated sodium channels, so the rod hyperpolarises and releases less glutamate.

Option by option

  • A. Increased cGMP level

    Phosphodiesterase activation lowers cGMP; it does not raise it.

  • B. Increased glutamate release

    Glutamate release falls in light because the cell hyperpolarises; it is highest in the dark.

  • C. Opening of voltage-gated calcium channels with depolarisation

    Calcium channels close, not open, when the rod hyperpolarises in light, and depolarisation is the state in the dark.

  • D. Closure of cGMP-gated sodium channels with hyperpolarisation (correct)

    Correct. Light lowers cGMP, closes the sodium channels and hyperpolarises the cell.

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 D, Closure of cGMP-gated sodium channels with hyperpolarisation. Light isomerises retinal in rhodopsin, activating transducin and phosphodiesterase, which breaks down cGMP.

Why is "Increased cGMP level" not the answer?

Phosphodiesterase activation lowers cGMP; it does not raise it.

Why is "Increased glutamate release" not the answer?

Glutamate release falls in light because the cell hyperpolarises; it is highest in the dark.

Why is "Opening of voltage-gated calcium channels with depolarisation" not the answer?

Calcium channels close, not open, when the rod hyperpolarises in light, and depolarisation is the state in the dark.

What concept does this question test?

It tests Special senses: vision in Physiology. The fall in cGMP closes cGMP-gated sodium channels, so the rod hyperpolarises and releases less glutamate.

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 Special senses: vision?

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.