Neurophysiology — Which mineral listed is most important for maintaining electrical potentials and excitability across nerve and muscle cell membranes (via voltage-gated channels and signaling)?

Introduction / Context:
Resting membrane potential and action potentials depend on ion gradients and the operation of voltage-gated channels. Among minerals, one cation plays a central role in triggering neurotransmitter release, excitation–contraction coupling, and modulation of channel gating. This question asks you to identify that mineral from the provided options.

Given Data / Assumptions:

• Ionic movements across membranes set electrical potentials.
• Voltage-gated channels are sensitive to extracellular and intracellular ion levels.
• Synaptic transmission and muscle contraction require a specific trigger ion.

Concept / Approach:
Although sodium and potassium primarily establish resting and action potentials, calcium is pivotal for electrical signaling by coupling depolarization to exocytosis at synapses and to contraction in muscle. Calcium influx through voltage-gated Ca2+ channels initiates neurotransmitter release, and sarcoplasmic reticulum Ca2+ release drives actin–myosin interaction in muscle. Hypocalcemia increases neuronal excitability (tetany), underscoring Ca2+’s stabilizing effect on membrane thresholds.

Step-by-Step Solution:

Verification / Alternative check:
Electrophysiologic recordings show Ca2+-dependent synaptic vesicle fusion and excitation–contraction coupling; calcium channel blockers reduce contractility and neurotransmission, highlighting Ca2+’s central role.

Why Other Options Are Wrong:

• Magnesium: modulates NMDA receptors and ATP complexes but is not the primary trigger ion.
• Manganese: a trace enzyme cofactor; limited role in membrane excitability.
• Iron: oxygen transport; no direct role in electrical potentials.
• Phosphorus: structural and metabolic roles (phosphates), not acute excitability control.

Common Pitfalls:
Equating “maintaining electrical potential” only with Na+/K+. While Na+ and K+ dominate the gradients, Ca2+ is the most relevant choice among the given minerals for excitability regulation and synaptic/muscle signaling.

Final Answer:
calcium.