Atropine works on which cranial nerve to reduce heart rate?

SGPGI Nursing Officer-2024

Pharmacology

Medium

Appeared in: SGPGI Nursing Officer-2024

Explanation

Atropine is a muscarinic antagonist, meaning it blocks the action of acetylcholine, the neurotransmitter for the parasympathetic nervous system.
The Vagus nerve (Cranial Nerve X) provides the primary parasympathetic input to the heart's sinoatrial (SA) node.
The normal function of the Vagus nerve is to slow the heart rate (a negative chronotropic effect), acting as a 'brake'.
By blocking this vagal tone, atropine removes the 'brake', allowing the heart rate to increase. This makes it a primary treatment for symptomatic bradycardia.
The question's phrasing is slightly confusing; atropine acts on the nerve that reduces heart rate, but the drug's ultimate effect is to increase it.

Option B: The Facial nerve (CN VII) is not involved in the autonomic regulation of heart rate. Its primary functions relate to facial expression, taste, and secretion from salivary and lacrimal glands.
Option C: The Trigeminal nerve (CN V) is responsible for facial sensation and motor control of chewing muscles. It has no direct function in controlling heart rate.
Option D: The Accessory spinal nerve (CN XI) is a motor nerve that innervates the sternocleidomastoid and trapezius muscles. Its function is related to head and shoulder movement, not cardiac control.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Atropine's mechanism of action on the autonomic nervous system, specifically its effect on cranial nerves and heart rate regulation as background academic context rather than a clinical decision trigger.
Atropine is a first-line emergency drug for treating symptomatic sinus bradycardia, a condition where a slow heart rate causes symptoms like dizziness, syncope, or hypotension.
Nurses must continuously monitor the patient's heart rate and rhythm on an ECG after administering atropine to evaluate its effectiveness and watch for adverse effects like excessive tachycardia or other arrhythmias.
Common side effects are due to its anticholinergic properties and include dry mouth, blurred vision, urinary retention, and constipation, which require nursing assessment and management.

How to Approach the Question

First, identify the key concepts in the question: the drug 'Atropine', its effect on 'heart rate', and its interaction with a 'cranial nerve'.
Recall the primary function of atropine in a clinical setting. It is used to treat bradycardia (a slow heart rate), which means its effect is to increase the heart rate.
Next, recall the autonomic nervous system's control over the heart. The parasympathetic system slows the heart rate, and the sympathetic system speeds it up.
The primary nerve of the parasympathetic system that innervates the heart is the Vagus nerve (CN X).
Connect these facts: To increase the heart rate, atropine must block the system that slows it down. Therefore, atropine must block the Vagus nerve.
Evaluate the options provided. The Facial, Trigeminal, and Accessory nerves have functions unrelated to direct cardiac rate control, allowing you to eliminate them confidently.

Concept Tested & Keywords

Concept Tested: Atropine's mechanism of action on the autonomic nervous system, specifically its effect on cranial nerves and heart rate regulation.
Stem keywords: Atropine, cranial nerve, heart rate
Lead-in keywords: works on which
Negative lead-in flag: false

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E6 Physiology Ganong 27e Vol 2 Part 1 p. 134-136

E6 Anatomy Applied Ashalatha 4e p. 431-433