Review Question - QID 109033

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Baroreceptors and Chemoreceptors Baroreceptors Baroreceptor reflex QID: 109033 (M1.CV.17.4765)

QID 109033 (Type "109033" in App Search)

A 28-year-old female comes to the emergency department complaining of heart palpitations. She has had multiple episodes of these in the past few months. She has found that if she wears tight clothing then sometimes these episodes will stop spontaneously. On presentation to the ED, she feels like her heart is pounding and reports feeling nauseous. She appears mildly diaphoretic. Her blood pressure is 125/75 mmHg, pulse is 180/min, and respirations are 22/min with an O2 saturation of 99% on room air. A neck maneuver is performed and her pulse returns to 90/min with improvement of her symptoms. Stimulation of afferent fibers from which nerve are most responsible for the resolution of her symptoms?

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Hypoglossal

1/164

Vagus

27%

44/164

Trigeminal

2/164

Glossopharyngeal

66%

108/164

Facial

0/164

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This patient is likely suffering from a supraventricular tachycardia that improves with carotid massage. Carotid massage increases the stretch on the carotid sinus leading to signal transmission via afferent fibers in the glossopharyngeal nerve.

Carotid massage causes stretch on the carotid sinus, a collection of nerves that respond to changes in blood pressure by detecting the stretch of the carotid blood vessels. This signal then stimulates afferent glossopharyngeal (CN IX) fibers that travel to the nucleus tractus solitarius in the medulla. The result is an increase in parasympathetic output carried by the vagus nerve (CN X) and withdrawal of the opposing sympathetic output to the cardiovascular system, which in sum lowers the heart rate in SVT.

Incorrect Answers:
Answer 1: The hypoglossal nerve (CN XII) mainly controls the tongue muscles and is not associated with baroreceptor stimulation.

Answer 2: The vagus nerve (CN X) is the afferent limb for the aortic arch baroreceptors and the efferent limb for the carotid sinus. The question asks about a neck massage which stimulates the carotid sinus rather than the aortic arch.

Answer 3: The trigeminal nerve (CN V) is involved in providing sensation to the face and innervating the muscles of mastication. It is not involved in baroreceptor firing.

Answer 5: The facial nerve (CN VII) is involved with motor innervation of intrinsic facial muscles and is not involved in baroreceptor firing.

Bullet Summary:
The carotid sinus responds to changes in blood pressure via vessel stretch and transmits information via the glossopharyngeal nerve for afferent limb and vagus nerve parasympathetic fibers for the efferent limb.

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