The response to hyperstimulation of vagus nerve is?

RUHS, Jaipur, PB B.Sc Nursing Entrance-2018

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2018

Explanation

The vagus nerve is the main component of the parasympathetic nervous system, which slows down heart functions.
Hyperstimulation (excessive stimulation) of the vagus nerve causes an exaggerated release of acetylcholine (ACh).
ACh acts on the heart's SA and AV nodes to drastically slow the heart rate and electrical conduction.
This profound slowing of the heart rate and rhythm is known as bradycardia or bradyarrhythmia.

Option A: The vagus nerve is part of the autonomic nervous system, which controls involuntary muscles like the heart and smooth muscles. Skeletal muscles are voluntary and are controlled by the somatic nervous system.
Option B: Similar to skeletal muscle relaxation, contraction is a function of the somatic nervous system, not the autonomic vagus nerve.
Option C: Tachyarrhythmia is a fast heart rhythm. This is the opposite effect of vagal stimulation. It is caused by the sympathetic nervous system ('fight or flight' response).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Autonomic Nervous System Physiology as background academic context rather than a clinical decision trigger.
Nurses may perform or instruct patients on vagal maneuvers (e.g., Valsalva maneuver, carotid sinus massage) to treat certain types of tachyarrhythmias by intentionally stimulating the vagus nerve to slow the heart rate.
Understanding this response is critical for recognizing potential side effects of medications that affect the autonomic nervous system or identifying vasovagal syncope, where a trigger causes a sudden drop in heart rate and blood pressure, leading to fainting.
What if the question asked about the effect of a vagolytic or antimuscarinic drug (like atropine)? The answer would be the opposite: Tachyarrhythmia, because these drugs block the vagus nerve's slowing effect on the heart, allowing the heart rate to increase.

How to Approach the Question

First, identify the key terms in the question: 'hyperstimulation' and 'vagus nerve'.
Recall the function of the vagus nerve. It is the primary nerve of the parasympathetic nervous system.
Remember the mnemonic 'rest and digest' for the parasympathetic system, which implies a slowing down of body functions, including heart rate.
Consider the term 'hyperstimulation', which means an excessive or exaggerated effect. Therefore, the effect on the heart will be a significant slowing.
Evaluate the options based on this understanding. 'Brady-' means slow, and 'Tachy-' means fast. 'Bradyarrhythmia' (slow, irregular rhythm) is the logical outcome of over-slowing the heart.
Eliminate options related to skeletal muscle, as the vagus nerve is part of the autonomic (involuntary) system, not the somatic (voluntary) system that controls skeletal muscles.

Concept Tested & Keywords

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E6 Pharmacology Katzung 16e pp. 174-176, 175-177, 177-179