Neurophysiology: reticular activating system: 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: reticular activating system

Sample item

A 55-year-old hypertensive man collapses and is deeply unresponsive. MRI shows a small haemorrhage in the dorsal upper pons and midbrain, with both cerebral hemispheres intact. What is the mechanism of his coma?

ABilateral destruction of the primary motor cortexBLoss of the medullary respiratory centreCInjury to the cerebellar vermisDDamage to the ascending reticular activating system, which projects to the cortex through the intralaminar thalamic nuclei

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

The answer and the reasoning

D. Damage to the ascending reticular activating system, which projects to the cortex through the intralaminar thalamic nuclei

Wakefulness depends on the ascending reticular activating system in the upper pons and midbrain, which activates the cortex through the thalamus and other relays. A small brainstem lesion here can cause coma although the hemispheres are normal, whereas hemispheric causes need bilateral extensive damage. Cortical arousal is the key function lost.

Option by option

A. Bilateral destruction of the primary motor cortex
Motor cortex destruction causes paralysis, not loss of consciousness.
B. Loss of the medullary respiratory centre
Medullary respiratory centre injury causes apnoea and is not the basis of coma.
C. Injury to the cerebellar vermis
The cerebellar vermis controls truncal coordination and not consciousness.
D. Damage to the ascending reticular activating system, which projects to the cortex through the intralaminar thalamic nuclei (correct)
Correct. Interruption of the ascending arousal system causes coma.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, Damage to the ascending reticular activating system, which projects to the cortex through the intralaminar thalamic nuclei. Wakefulness depends on the ascending reticular activating system in the upper pons and midbrain, which activates the cortex through the thalamus and other relays.

Why is "Bilateral destruction of the primary motor cortex" not the answer?

Motor cortex destruction causes paralysis, not loss of consciousness.

Why is "Loss of the medullary respiratory centre" not the answer?

Medullary respiratory centre injury causes apnoea and is not the basis of coma.

Why is "Injury to the cerebellar vermis" not the answer?

The cerebellar vermis controls truncal coordination and not consciousness.

What concept does this question test?

It tests Neurophysiology: reticular activating system in Physiology. A small brainstem lesion here can cause coma although the hemispheres are normal, whereas hemispheric causes need bilateral extensive damage. Cortical arousal is the key function lost.

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: reticular activating system?

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.