Question

What happens when the cell fires when crossing -55mV?

1) The membrane potential fluctuates and causes the rapid opening and closing of particular voltage gated ion channels
2) The cell becomes inactive and does not fire
3) The cell fires continuously without any fluctuations
4) The membrane potential stabilizes at -55mV

Answer 1

The crossing of the -55mV threshold by the cell's membrane potential initiates an action potential, characterized by the depolarization and repolarization of the neuron through the opening and closing of Na+ and K+ voltage-gated ion channels.

Step-by-step explanation:

When the cell's membrane potential crosses -55mV, an action potential is triggered. This potential fluctuates and leads to the rapid opening and closing of voltage-gated ion channels. Specifically, this involves the opening of Na+ channels allowing sodium ions to rush into the neuron causing depolarization, which changes the membrane potential from -70mV to about +30mV. Following depolarization, to repolarize the neuron K+ channels open allowing potassium to exit the cell. Consequently, Na+ channels inactivate preventing further entry of sodium. As the K+ exits, the neuron's membrane potential is restored towards the resting potential. The action potential is an all-or-nothing event, so the neuron does not fire continuously without any fluctuations nor does it become inactive after firing.