Biology Nervous Coordination UHS 2024
PMDC Verified Question 14 of 86
Depolarization during conduction of nerve impulse is due to:
A
Inward movement of Na+
B
Outward movement of Na+
C
Inward movement of K+
D
Outward movement of K+
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Inward movement of Na+
Concept:

An action potential occurs when the neuron briefly reverses its internal charge from negative to positive (depolarization).

Solution:

  • When a stimulus reaches threshold, voltage-gated sodium channels burst open. Because sodium is highly concentrated outside the cell, there is a massive inward movement (influx) of \(\text{Na}^+\) ions into the neuron, rapidly changing the membrane potential to +50mV.


Why other options are incorrect:

  • Outward movement of K+: This causes repolarization (returning to negative), not depolarization.


  • Outward Na+ / Inward K+: This ion direction is forced by the slow \(\text{Na}^+/\text{K}^+\) pump to maintain the resting state, not the rapid action potential.

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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