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Question #47432
The Question
In an experimental setup, a chemical synapse is treated with a drug that acts as a competitive inhibitor for excitatory neurotransmitter receptors on the postsynaptic membrane, significantly reducing their binding affinity without completely blocking them. Despite high-frequency stimulation of the presynaptic neuron and normal exocytosis of neurotransmitters, the postsynaptic neuron fails to fire an action potential. Which of the following best explains this physiological failure?
Options
- A.
The drug induces a prolonged absolute refractory period in the postsynaptic membrane, preventing the opening of voltage-gated Na+ channels.
- B.
The reduced receptor affinity increases synaptic delay, causing individual Excitatory Postsynaptic Potentials (EPSPs) to dissipate before effective temporal summation can occur at the axon hillock.
- C.
The competitive inhibitor alters the differential permeability of the postsynaptic membrane, causing a rapid efflux of K+ ions that neutralizes the EPSPs.
- D.
The decreased affinity prevents spatial summation of EPSPs from the single stimulated presynaptic neuron, keeping the membrane potential below threshold.
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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
Synaptic Delay Determinant|Neurotransmitter Receptor Specificity|Acetylcholinesterase
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between temporal summation (time-dependent, single synapse) and spatial summation (space-dependent, multiple synapses), while understanding the kinetic nature of EPSPs as graded potentials that decay.
The common misconception is treating competitive inhibition purely as an 'on/off' switch, rather than understanding its effect on reaction rates (synaptic delay) and how that specifically disrupts the timing required for temporal summation.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Neural Control and Coordination - Class 11 |
| Concept | Synaptic Delay Determinant |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |