Cardiovascular reflexes: Cushing reflex: 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 · Cardiovascular reflexes: Cushing reflex

Sample item

A 30-year-old man with a head injury and rising intracranial pressure has blood pressure 190/100 mmHg, heart rate 48 per minute and irregular breathing. What is the most direct cause of his bradycardia?

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

The answer and the reasoning

D. Baroreceptor reflex activation by the high arterial pressure

Raised intracranial pressure compresses cerebral vessels and causes ischaemia of the medullary vasomotor centre, which drives intense sympathetic vasoconstriction and hypertension. The high arterial pressure stimulates the carotid and aortic baroreceptors, which reflexly increase vagal tone and slow the heart. Hypertension, bradycardia and irregular respiration form the Cushing triad.

Option by option

  • A. Direct vagal stimulation by the injured cortex

    The cortex does not directly drive the vagal outflow in this reflex.

  • B. Withdrawal of sympathetic tone to the sinoatrial node by the brain injury

    Sympathetic tone is increased rather than withdrawn, which is why pressure is high.

  • C. Atrial stretch receptor activation by raised venous return

    Atrial stretch receptors would produce tachycardia, as in the Bainbridge reflex.

  • D. Baroreceptor reflex activation by the high arterial pressure (correct)

    Correct. The bradycardia is a baroreflex response to the ischaemia-driven hypertension.

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, Baroreceptor reflex activation by the high arterial pressure. Raised intracranial pressure compresses cerebral vessels and causes ischaemia of the medullary vasomotor centre, which drives intense sympathetic vasoconstriction and hypertension.

Why is "Direct vagal stimulation by the injured cortex" not the answer?

The cortex does not directly drive the vagal outflow in this reflex.

Why is "Withdrawal of sympathetic tone to the sinoatrial node by the brain in…" not the answer?

Sympathetic tone is increased rather than withdrawn, which is why pressure is high.

Why is "Atrial stretch receptor activation by raised venous return" not the answer?

Atrial stretch receptors would produce tachycardia, as in the Bainbridge reflex.

What concept does this question test?

It tests Cardiovascular reflexes: Cushing reflex in Physiology. The high arterial pressure stimulates the carotid and aortic baroreceptors, which reflexly increase vagal tone and slow the heart. Hypertension, bradycardia and irregular respiration form the Cushing triad.

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 Cardiovascular reflexes: Cushing reflex?

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.