Biology Nervous Coordination KMU 2024
PMDC Verified Question 22 of 86
Diffusion of ____ across the post synaptic membrane causes it to depolarize.
A
Chloride ions
B
Potassium ions
C
Calcium ions
D
Sodium ions
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Sodium ions
Concept:

Depolarization is defined as the interior of a cell becoming less negative, which requires the rapid entry of a positive ion.

Solution:

  • When an excitatory synapse is activated, ligand-gated channels open and allow an overwhelming influx (diffusion) of positively charged Sodium (\(\text{Na}^+\)) ions into the postsynaptic neuron. This neutralizes the resting negative charge, causing depolarization.


Why other options are incorrect:

  • Chloride ions (\(\text{Cl}^-\)): Entering the cell makes it more negative (hyperpolarization/inhibition).


  • Potassium ions (\(\text{K}^+\)): Exiting the cell removes positive charge, leading to repolarization or hyperpolarization.


  • Calcium: Works primarily in the presynaptic terminal, not for bulk postsynaptic depolarization.

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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