Combined AIIMS - 2020 (Jodhpur, Bhopal, Patna, Raipur)
Applied Physiology
Easy
What is the action of vagus nerve stimulation on heart rate?
Appeared in: Combined AIIMS - 2020 (Jodhpur, Bhopal, Patna, Raipur)
Explanation
- The vagus nerve is the main nerve of the parasympathetic division of the autonomic nervous system that innervates the heart.
- Stimulation of the vagus nerve releases the neurotransmitter acetylcholine (ACh).
- ACh acts on the sinoatrial (SA) node, the heart's primary pacemaker, to slow down its firing rate.
- This action results in a decreased heart rate, an effect known as a negative chronotropic effect.
- This is a cardioinhibitory function, contrasting with the cardioacceleratory function of the sympathetic nervous system.
Why Other Options Were Wrong
- Option B: Increasing the heart rate is the primary function of the sympathetic nervous system, not the parasympathetic (vagal) system.
- Option C: Stimulation of a nerve implies a change from the baseline or normal state. Vagal stimulation actively slows the heart rate below its normal resting state.
- Option D: This option is incorrect because vagus nerve stimulation has a very specific and predictable effect on the heart rate.
Related Visual
Clinical Relevance
- Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The concept tested is the physiological effect of parasympathetic nervous system stimulation, specifically via the vagus nerve, on heart rate as background academic context rather than a clinical decision trigger.
- Nurses may instruct patients to perform vagal maneuvers (e.g., carotid sinus massage, Valsalva maneuver) to slow a dangerously fast heart rate, as seen in conditions like supraventricular tachycardia (SVT).
- Understanding this concept is crucial for administering medications. For example, atropine is a drug that blocks vagal effects and is used to treat symptomatic bradycardia (abnormally slow heart rate).
- A constant, moderate level of vagal activity, known as 'vagal tone,' keeps the resting heart rate lower than the heart's intrinsic pacemaker rate. Higher vagal tone is often associated with better cardiovascular health.
How to Approach the Question
- First, identify the key terms in the question: 'vagus nerve stimulation' and 'heart rate'.
- Recall the two main divisions of the autonomic nervous system: sympathetic ('fight or flight') and parasympathetic ('rest and digest').
- Associate the vagus nerve with the parasympathetic nervous system.
- Remember the primary function of the parasympathetic system on the heart is to slow it down and conserve energy.
- Conversely, remember the sympathetic system's function is to speed the heart up for action.
- Based on this, conclude that stimulating the vagus nerve (parasympathetic) will decrease the heart rate.
Concept Tested & Keywords
- Concept Tested: The concept tested is the physiological effect of parasympathetic nervous system stimulation, specifically via the vagus nerve, on heart rate.
- Stem keywords: vagus nerve stimulation, heart rate, action
- Lead-in keywords: What is
Question ID
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Reference Book
E6 Physiology Ganong 27e Vol 2 Part 1 pp. 134-136, 135-137
E6 Physiology Review Sembulingam 5e p. 120-122
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