Neurophysiology and special senses: narcolepsy: 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: narcolepsy

Sample item

A 19-year-old has irresistible daytime sleep attacks, sudden loss of muscle tone when laughing and hallucinations on falling asleep. Cerebrospinal fluid levels of a peptide made in the lateral hypothalamus are very low. Which peptide is deficient?

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

The answer and the reasoning

B. Hypocretin

Loss of hypocretin (orexin) neurons in the lateral hypothalamus causes narcolepsy with cataplexy. These neurons stabilise wakefulness, and without them REM sleep phenomena such as atonia and dream imagery intrude into waking.

Option by option

  • A. Neuropeptide Y

    Neuropeptide Y is an appetite-stimulating peptide of the arcuate nucleus.

  • B. Hypocretin (correct)

    Correct. Loss of hypocretin neurons causes narcolepsy with cataplexy.

  • C. Cholecystokinin

    Cholecystokinin is a gut and brain satiety peptide and is not the deficient peptide here.

  • D. Melatonin

    Melatonin is a pineal hormone and is not the lateral hypothalamic peptide lost in narcolepsy.

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, Hypocretin. Loss of hypocretin (orexin) neurons in the lateral hypothalamus causes narcolepsy with cataplexy.

Why is "Neuropeptide Y" not the answer?

Neuropeptide Y is an appetite-stimulating peptide of the arcuate nucleus.

Why is "Cholecystokinin" not the answer?

Cholecystokinin is a gut and brain satiety peptide and is not the deficient peptide here.

Why is "Melatonin" not the answer?

Melatonin is a pineal hormone and is not the lateral hypothalamic peptide lost in narcolepsy.

What concept does this question test?

It tests Neurophysiology and special senses: narcolepsy in Physiology. These neurons stabilise wakefulness, and without them REM sleep phenomena such as atonia and dream imagery intrude into waking.

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 Neurophysiology and special senses: narcolepsy?

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.