Activation of peripheral chemoreceptors contributes to the regulation of breathing and can induce changes in autonomic nervous system function. Which of the following statements about the chemoreflex regulation of breathing is INCORRECT.

Question

BlackTom AI · Accepted Answer

Activation of glomus (type I) cells in the carotid body causes an increase — not a decrease — in afferent nerve activity. Peripheral chemoreceptors (carotid and aortic bodies) detect hypoxia, hypercapnia and acidosis and communicate this to the brainstem to increase ventilation and sympathetic outflow.

Relevant knowledge points and concepts:
- Carotid body glomus (type I) cells are the primary O2 sensors in the periphery; central chemoreceptors respond mainly to CO2/H+ in the CSF.
- The transduction mechanism: inhibition of O2-sensitive K+ channels → cell depolarization → opening of voltage-gated Ca2+ channels → Ca2+ influx → vesicular release of neurotransmitters (ATP, ACh, dopamine).
- Neurotransmitters bind receptors on afferent terminals (carotid sinus nerve, branch of glossopharyngeal) → increased action potential frequency to the nucleus tractus solitarius (NTS) → increased ventilation and autonomic responses.

Step-by-step reasoning (mechanistic sequence):
1. Arterial PO2 falls below the normal range (especially <60 mmHg).  
2. O2-sensitive background K+ channels in glomus cells are inhibited by low O2.  
3. Reduced K+ efflux causes membrane depolarization of the glomus cell.  
4. Depolarization opens voltage-gated Ca2+ channels; Ca2+ enters the cell.  
5. Elevated intracellular Ca2+ triggers exocytosis of neurotransmitter-filled vesicles (ATP, ACh, dopamine).  
6. These transmitters activate ionotropic receptors (e.g., P2X) on the afferent nerve ending, producing excitatory postsynaptic potentials and increasing firing rate of the afferent nerve.  
7. Increased afferent firing to the NTS elevates respiratory drive and raises sympathetic activity.

Why the given statement is incorrect:
The statement claims that neurotransmitter release reduces afferent activity. In fact, transmitter release from glomus cells is excitatory; it increases the firing frequency of afferent fibers. Experimental recordings of the carotid sinus nerve show increased discharge during hypoxia, consistent with excitatory transmitter action.

Why other plausible choices (not listed) would be incorrect as the "INCORRECT" choice:
Typical true statements include that peripheral chemoreceptor activation increases ventilation and sympathetic tone, and that carotid bodies are very sensitive to PO2 changes — these are correct and therefore would not be the incorrect option.

Conclusion: The provided answer — "The activation of glomus cells and the subsequent release of neurotransmitters results in reduced activity in the afferent nerve" — is indeed incorrect; neurotransmitter release increases afferent activity. This confirms the final answer.

Activation of peripheral chemoreceptors contributes to the regulation of breathing and can induce changes in autonomic nervous system function. Which of the following statements about the chemoreflex regulation of breathing is INCORRECT.Single choice

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