Biology Nervous Coordination MDCAT 2019
PMDC Verified Question 74 of 86
In an action potential, the permeability of sodium ions in the neuron increases due to:
A
Repolarization
B
The action of the acetylcholinesterase enzyme
C
The opening of sodium channels/gates
D
Sodium ions forming an ionic bonding
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: The opening of sodium channels/gates
Concept:

Changes in membrane permeability are controlled by voltage-gated ion channels embedded in the lipid bilayer.

Solution:

  • When the membrane reaches threshold potential, voltage-gated sodium channels undergo a conformational change and open. This drastically increases the membrane's permeability to \(\text{Na}^+\), allowing a massive influx of sodium down its electrochemical gradient, triggering depolarization.


Why other options are incorrect:

  • Repolarization: Occurs due to the closing of sodium gates and the opening of potassium gates.


  • Acetylcholinesterase: An enzyme that breaks down neurotransmitters in the synaptic cleft, unrelated to axonal sodium gates.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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