Respiratory system: central hypoventilation and automatic breathing: 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 · Respiratory system: central hypoventilation and automatic breathing

Sample item

A 3-month-old infant breathes adequately when awake or stimulated, but during sleep the breathing becomes shallow or stops and the PaCO2 rises. Which description fits the underlying disturbance?

ALoss of the medullary automatic control of breathing, with voluntary cortical control preservedBObstruction of the upper airway by pharyngeal collapseCFailure of the voluntary cortical pathway to the respiratory musclesDParalysis of the diaphragm from phrenic nerve injury

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

The answer and the reasoning

A. Loss of the medullary automatic control of breathing, with voluntary cortical control preserved

Breathing is controlled by two separate systems: the automatic brainstem rhythm with its chemoreceptor input, and voluntary cortical control that reaches the motor neurones through the corticospinal tracts. In congenital central hypoventilation (Ondine's curse) the automatic drive fails during sleep, but breathing is possible when the cortex takes over.

Option by option

A. Loss of the medullary automatic control of breathing, with voluntary cortical control preserved (correct)
Correct. The automatic system fails in sleep while voluntary control keeps breathing going when awake.
B. Obstruction of the upper airway by pharyngeal collapse
Airway obstruction gives effort without flow, whereas here the ventilatory effort itself is absent.
C. Failure of the voluntary cortical pathway to the respiratory muscles
If the voluntary pathway failed, the infant could still breathe automatically and would not stop in sleep alone.
D. Paralysis of the diaphragm from phrenic nerve injury
Diaphragm paralysis would persist when awake and would not depend on sleep.

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 A, Loss of the medullary automatic control of breathing, with voluntary cortical control preserved. Breathing is controlled by two separate systems: the automatic brainstem rhythm with its chemoreceptor input, and voluntary cortical control that reaches the motor neurones through the corticospinal tracts.

Why is "Obstruction of the upper airway by pharyngeal collapse" not the answer?

Airway obstruction gives effort without flow, whereas here the ventilatory effort itself is absent.

Why is "Failure of the voluntary cortical pathway to the respiratory muscles" not the answer?

If the voluntary pathway failed, the infant could still breathe automatically and would not stop in sleep alone.

Why is "Paralysis of the diaphragm from phrenic nerve injury" not the answer?

Diaphragm paralysis would persist when awake and would not depend on sleep.

What concept does this question test?

It tests Respiratory system: central hypoventilation and automatic breathing in Physiology. In congenital central hypoventilation (Ondine's curse) the automatic drive fails during sleep, but breathing is possible when the cortex takes over.

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 Respiratory system: central hypoventilation and automatic breathing?

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.