neurobio 5 ch 4 of Bear book: the action potential part 1 (overshoot undershoot node of ranvier t

negative

positive

the inside of the membrane has a negative electrical potential electrical potential, there is a large driving force on sodium ions Therefore, sodium ions rush into the cell through the open sodium channels, causingthe membrane to rapidly depolarize

threshold is the membrane potential at which enough voltage-gated sodium channels open so that the relative ionic permeability of the membrane favors sodium over potassium.

because the relative permeability of the membrane greatly favors sodium, the membrane potential goes to a value close to E_Na which is greater than 0 mV

the behavior of two types of channel contributes to the falling phase. First,m the voltage gated sodium channels inactivate. Second, the voltage-gated potassium channels finally open (triggered to do so 1 msec earlier by the depolarization of the membrane). There is a great driving force on K ions when the membrane is strongly depolarized. Therefore, K ions rush out of the cell through the open channels, causing the membrane potential to become negative again.

the open voltage-gated potassium channels add to the resting potassium membrane permeability. Because there is very little sodium permeability, the membrane potential goes toward E_K, causing a hyperpolarization relative to the resting membrane potential until the voltage gated potassium channels close again

sodium channels inactivate when the membrane becomes strongly depolarized. They cannot be activated again and another action potential cannot be generated, until the membrane potential goes sufficiently negative to deinactivate the channels

conduction of the action potential in one direction

a sophisticated voltmeter that displays electrical signals in graphical form