Transtentorial brainstem injury localized to the upper pons disrupts a group of neurons whose normal function is to modulate the inspiratory off-switch. Damage to which structure produces apneustic breathing characterized by prolonged inspiratory pauses?
- A Pontine respiratory group (pneumotaxic center) in the upper pons ✓
- B Pre-Botzinger complex of the ventrolateral medulla
- C Retrotrapezoid nucleus of the ventral medullary surface
- D Nucleus ambiguus fibers running with the vagus nerve
Correct answer: A. Pontine respiratory group (pneumotaxic center) in the upper pons
Explanation
The pontine respiratory group in the upper pons (parabrachial complex) inhibits the inspiratory ramp and shortens inspiration; loss of this input, especially combined with vagotomy, removes the secondary off-switch and produces apneusis. The pre-Botzinger complex generates the basic rhythm itself rather than timing the off-switch, and the retrotrapezoid nucleus subserves central chemoreception.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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