Ion channels. Animation showing first a voltage-gated sodium channel and then a ligand-gated ion channel. Ion channels are membrane-spanning proteins (green) that form pores in cell membranes that allow the movement of inorganic ions (red dot) into and out of the cell. Voltage-gated channels open in response to an electrical impulse across the membrane that reverses its polarity. Ligand-gated channels open in response to a substance (blue dot), such as a neurotransmitter, binding to the channel. The binding of the ligand causes a conformational change in the channel protein, opening its pore.
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