Neurophysiology and special senses: hair cell transduction: 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 · Neurophysiology and special senses: hair cell transduction

Sample item

When the stereocilia of an inner hair cell bend towards the tallest row, the cell depolarises. Which ion carries the inward current, and why is that notable?

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

The answer and the reasoning

B. Potassium, because endolymph is rich in K+ and the hair cell interior is strongly negative

Endolymph in scala media has a high potassium concentration and a positive potential, while the hair cell interior is strongly negative. This large electrochemical difference drives K+ inward through the mechanically gated channels, depolarising the cell.

Option by option

  • A. Chloride, entering because the cell interior is positive

    The hair cell interior is negative, so chloride would tend to leave and is not the current.

  • B. Potassium, because endolymph is rich in K+ and the hair cell interior is strongly negative (correct)

    Correct. K+ enters from the potassium-rich endolymph, an unusual feature among extracellular fluids.

  • C. Sodium, because endolymph is rich in Na+ like other extracellular fluid

    Endolymph is rich in potassium, unlike most extracellular fluids, so Na+ is not the main current.

  • D. Calcium, entering from the perilymph through voltage-gated channels first

    Calcium entry follows depolarisation and triggers transmitter release, but it is not the initial current.

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 B, Potassium, because endolymph is rich in K+ and the hair cell interior is strongly negative. Endolymph in scala media has a high potassium concentration and a positive potential, while the hair cell interior is strongly negative.

Why is "Chloride, entering because the cell interior is positive" not the answer?

The hair cell interior is negative, so chloride would tend to leave and is not the current.

Why is "Sodium, because endolymph is rich in Na+ like other extracellular flu…" not the answer?

Endolymph is rich in potassium, unlike most extracellular fluids, so Na+ is not the main current.

Why is "Calcium, entering from the perilymph through voltage-gated channels f…" not the answer?

Calcium entry follows depolarisation and triggers transmitter release, but it is not the initial current.

What concept does this question test?

It tests Neurophysiology and special senses: hair cell transduction in Physiology. This large electrochemical difference drives K+ inward through the mechanically gated channels, depolarising the cell.

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 Neurophysiology and special senses: hair cell transduction?

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.