Events of action potential   Na+ K+ OUT Na+ IN A Quick Look Back By now you should be familiar with the structure of a basic nerve cell and the events that generate the action potential at the axon hillock. The important ions that are involved in the action potential are sodium (Na+) and potassium (K+). Each of these ions has its own special voltage-gated channel that opens in response to the depolarization of the cell membrane. The Na+ channels open quickly, while the K+ channels open a little later. The movement of the ions across the membrane changes the membrane potential and produces the action potential at the axon hillock. K+

Nerve Physiology Membrane Potential established by a cell membrane’s ability to alter its permeability Defined as a charge across the cell membrane that is due to an unequal distribution of ions

Nerve Physiology 2 types of Membrane Potentials Resting membrane potential Action potential (nerve impulse)

axon - - - - - - - - - - - - - - - K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ Na+ + - - - Na+ + Na+ - - + K+ - K+ Na+ K+ K+ - K+ K+ + Na+ + Fixed anions - K+ - Na+ Na+ + + Na+ K+ K+ Na+ - Na+ Na+ - K+ + + K+ K+ K+ - + - + - - + + + +

Nerve Physiology Action membrane potential (AP)-depolarization and repolarization constitute and AP 1. when a neuron is stimulated (in action produces nerve impulse) 2. more Na+ ions inside cell membrane more K+ ions outside

Nerve Physiology Action membrane potential 3. positively (+) charged inside negatively (-)charged on the outside (ie Charge Reversal) 4. occurs in 2 stages stage 1= depolarization stage 2 = repolarization

Nerve Physiology Action membrane potential Depolarization = stimulus leads to Na+ ions rushing into neuron  makes inside more positive (less negative)

RMP axon Depolarization of Action Potential - - - - - - - K+ K+ K+ K+ Na+ - - - Na+ - K+ - K+ K+ K+ K+ K+ + Na+ + Fixed anions - K+ Na+ Na+ K+ K+ Na+ K+ + K+ K+ K+ -

Nerve Physiology Action membrane potential Repolarization = occurs right after depolarization K+ (potassium ions) rush out of neuron cell  makes inside (-) charged.

RMP axon Depolarization of Action Potential Repolarization of Action Potential axon + Na+ - - - Na+ - K+ - K+ + Na+ + Fixed anions - Na+ Na+ K+ Na+ + K+ K+ -

Nerve Physiology Action membrane potential Repolarization Sodium Potassium pump reestablishes ionic gradient for Sodium and Potassium

Events of action potential   Na+ K+ OUT Na+ IN A Quick Look Back By now you should be familiar with the structure of a basic nerve cell and the events that generate the action potential at the axon hillock. The important ions that are involved in the action potential are sodium (Na+) and potassium (K+). Each of these ions has its own special voltage-gated channel that opens in response to the depolarization of the cell membrane. The Na+ channels open quickly, while the K+ channels open a little later. The movement of the ions across the membrane changes the membrane potential and produces the action potential at the axon hillock. K+

An AP can propagate itself across the surface of the PM. The depolarization caused by the Na+ influx in one particular area of the PM causes voltage-gated channels in the adjacent membrane to open. The resulting ionic influx then causes voltage-gated channels to open in the next patch of membrane and so on and so on. Thus the AP propagates itself.