In a nerve fiber, the magnitude of the action potential overshoot typically depends on the______________?
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Answer: C. extracellular sodium concentration
Explanation
The peak height of an action potential depends primarily on the rapid influx of sodium ions. Extracellular sodium concentration directly determines the electrochemical gradient driving sodium into the nerve fiber. A higher external sodium concentration results in a greater positive overshoot during the depolarization phase. Action potentials are rapid electrical impulses characterized by depolarization, overshoot, and repolarization phases. Voltage-gated sodium channels open rapidly when the membrane potential reaches the specific threshold level. The Nernst equation demonstrates how ionic concentration gradients determine the equilibrium potential for sodium.
Normal nerve conduction relies heavily on maintaining precise extracellular and intracellular electrolyte concentrations. Pathological electrolyte imbalances can alter action potential characteristics and impair neurological signal transmission. Clinical evaluations of nerve function often consider systemic sodium levels as a contributing physiological factor. The magnitude of the stimulus affects the frequency of action potentials rather than the single overshoot height. Intracellular potassium concentration primarily influences the resting membrane potential rather than the action potential peak. The resting membrane potential sets the baseline voltage but does not directly determine the sodium-driven overshoot.
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