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Question #46381
The Question
The neural centre in the medulla oblongata regulates cardiac activity through the Autonomic Nervous System (ANS). A patient accidentally ingests a plant alkaloid that acts as a potent agonist for the neurotransmitter released by the vagus nerve. Despite the physiological stress, the patient exhibits severe bradycardia and reduced cardiac output. Which of the following best describes the mechanism of this alkaloid at the Sino-Atrial (SA) node?
Options
- A.
It binds to adrenergic receptors, competitively inhibiting norepinephrine and preventing the SA node from reaching the threshold potential.
- B.
It mimics acetylcholine, causing hyperpolarization of the SA node, which decreases the rate of heartbeat and the speed of action potential conduction.
- C.
It stimulates the sympathetic nerve fibres to release acetylcholine, which directly decreases the strength of ventricular contraction.
- D.
It blocks the parasympathetic neural signals from the medulla oblongata, leading to a prolonged refractory period in the SA node.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Medulla_Oblongata|Vagus_Nerve|Acetylcholine|Norepinephrine
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students must connect the vagus nerve to the parasympathetic nervous system and its specific neurotransmitter (acetylcholine).
The 'Plus' depth requires understanding that parasympathetic bradycardia is achieved via hyperpolarization of the SA node, and distinguishing between an agonist (mimics) and an antagonist (blocks).
Common misconception: Confusing adrenergic (sympathetic) and cholinergic (parasympathetic) receptor specificities.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Body Fluids and Circulation - Class 11 |
| Concept | Regulation of Cardiac Activity |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |