Which ions have the highest extracellular concentrations in typical neurons: Na+ or K+?
QUESTION
If extracellular K+ rises (hyperkalemia), what is the immediate effect on resting Vm?
QUESTION
During the rising phase of an action potential, which voltage-gated channel opens first?
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ANSWER
Voltage-gated Na+ channels. These channels activate at threshold, allowing rapid sodium influx that drives the membrane potential toward the sodium equilibrium potential.