Activation gates in the cell membrane for voltage-gated sodium ion channels open into theMultiple ChoiceCytoplasmNucleusEndoplasmic reticulumExtracellular fluid

The membrane potential at which voltage-gated sodium channels open is called .

An action potential arriving at the presynaptic terminal causesMultiple Choicevoltage-gated sodium ion channels to open, and sodium ions to diffuse out of the cell.voltage-gated calcium ion channels to open, and calcium ions to diffuse into the cell.voltage-gated sodium ion channels to open, and sodium ions to diffuse into the cell.ligand-gated sodium channels to open, and sodium ions to diffuse out of the cell.acetylcholine to diffuse into the cell.

The cell membrane immediately adjacent to an action potential depolarizes because ofMultiple ChoiceMembrane receptorsMembrane permeabilitySodium ionsLocal currents

At resting membrane potential, voltage-gated potassium ion channels are open.

A recently depolarized area of a cell membrane cannot generate an action potential because of theMultiple Choicehigh concentration of sodium ions in the extracellular fluid.the high concentration of potassium ions in the cytoplasm.absolute refractory period.presence of receptor sites on the membrane.