With regards to the role of different respiratory nuclei in the generation of a three phase respiratory rhythm, which ONE of the following statements about the role of the pontine respiratory group (PRG) is MOST CORRECT?

Question

With regards to the role of different respiratory nuclei in the generation of a three phase respiratory rhythm, which ONE of the following statements about the role of the pontine respiratory group (PRG) is MOST CORRECT?

BlackTom AI · Accepted Answer

Pontine respiratory group (PRG) neurons (Kölliker-Fuse and parabrachial nuclei) are critical for producing and timing the post‑inspiratory phase of the respiratory cycle.

1. Relevant knowledge points and concepts
- Normal mammalian respiratory rhythm has three phases: Inspiration (I), post‑inspiration (post‑I, early expiration), and augmenting expiration (aug‑E, late expiration).
- The medulla (pre‑Bötzinger complex, Bötzinger complex, rostroventral medulla) generates the basic inspiratory and expiratory rhythm; the pons (PRG) shapes phase transitions, especially terminating inspiration and sustaining post‑I activity.
- Pontine transection or lesions (decerebrate/prepontine preparations) remove PRG influence and alter the three‑phase pattern.

2. Step‑by‑step reasoning
- PRG provides phasic drive and timing signals that activate post‑I neurons and enforce a distinct early expiratory phase.
- With intact PRG: sequence is I → post‑I → aug‑E.
- After pontine transection: the PRG input is lost, so post‑I neurons lack the excitatory/phase‑timing input that makes the post‑I phase distinct.
- Experimentally, this produces loss of the post‑inspiratory phase and can produce apneustic (prolonged inspiration) breathing; the remaining medullary circuits still generate inspiration and aug‑E activity.

3. Intermediate steps / observations
- Observe pre‑transection: clear post‑I firing between inspiration and aug‑E.
- After transection: post‑I firing ceases; inspiratory bursts prolong and transition directly to aug‑E — so two phases remain.

4. Why the correct answer is correct
- The statement “Following pontine transection, post‑inspiratory neurons are no longer active” matches physiological and experimental evidence that the PRG is necessary to sustain post‑I activity and the three‑phase pattern.

5. Why other options are incorrect
- “Following pontine transection, augmenting expiratory neurons are no longer active”: incorrect — aug‑E neurons are largely medullary and remain active after pontine removal.
- “Removal of the pons has no impact on the three phase respiratory pattern”: incorrect — removal abolishes the post‑I phase, altering the pattern.
- “The pattern of respiratory motor output remains the same following the removal of the pons”: incorrect — motor output changes (loss of post‑I, possible apneusis).

6. Conclusion
This reasoning confirms the correct answer: Following pontine transection, post‑inspiratory neurons are no longer active.

With regards to the role of different respiratory nuclei in the generation of a three phase respiratory rhythm, which ONE of the following statements about the role of the pontine respiratory group (PRG) is MOST CORRECT?Single choice

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