In an animal experiment, the brainstem is transected between the pons and medulla and the vagus nerves are cut bilaterally. The resulting breathing pattern is:

• A Apneusis, prolonged inspiratory pauses ✓
• B Normal eupnoea
• C Rapid regular panting
• D Sustained apnoea

Explanation

The pontine pneumotaxic centre, in the parabrachial and Kolliker-Fuse nuclei, switches off inspiration and shortens the inspiratory ramp; the vagal pulmonary stretch receptors perform the same braking function. Removing both inputs leaves the medullary inspiratory neurons unopposed, producing apneusis, long tonic inspiratory spasms interrupted by brief expirations. Transection above the pons leaves breathing normal, and the medulla alone still generates a rhythmic gasping pattern rather than apnoea.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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