<P> Each excitable patch of membrane has two important levels of membrane potential : the resting potential , which is the value the membrane potential maintains as long as nothing perturbs the cell , and a higher value called the threshold potential . At the axon hillock of a typical neuron , the resting potential is around -- 70 millivolts ( mV ) and the threshold potential is around -- 55 mV . Synaptic inputs to a neuron cause the membrane to depolarize or hyperpolarize ; that is , they cause the membrane potential to rise or fall . Action potentials are triggered when enough depolarization accumulates to bring the membrane potential up to threshold . When an action potential is triggered , the membrane potential abruptly shoots upward and then equally abruptly shoots back downward , often ending below the resting level , where it remains for some period of time . The shape of the action potential is stereotyped ; this means that the rise and fall usually have approximately the same amplitude and time course for all action potentials in a given cell . ( Exceptions are discussed later in the article ) . In most neurons , the entire process takes place in about a thousandth of a second . Many types of neurons emit action potentials constantly at rates of up to 10 -- 100 per second . However , some types are much quieter , and may go for minutes or longer without emitting any action potentials . </P>
<P> Each excitable patch of membrane has two important levels of membrane potential : the resting potential , which is the value the membrane potential maintains as long as nothing perturbs the cell , and a higher value called the threshold potential . At the axon hillock of a typical neuron , the resting potential is around -- 70 millivolts ( mV ) and the threshold potential is around -- 55 mV . Synaptic inputs to a neuron cause the membrane to depolarize or hyperpolarize ; that is , they cause the membrane potential to rise or fall . Action potentials are triggered when enough depolarization accumulates to bring the membrane potential up to threshold . When an action potential is triggered , the membrane potential abruptly shoots upward and then equally abruptly shoots back downward , often ending below the resting level , where it remains for some period of time . The shape of the action potential is stereotyped ; this means that the rise and fall usually have approximately the same amplitude and time course for all action potentials in a given cell . ( Exceptions are discussed later in the article ) . In most neurons , the entire process takes place in about a thousandth of a second . Many types of neurons emit action potentials constantly at rates of up to 10 -- 100 per second . However , some types are much quieter , and may go for minutes or longer without emitting any action potentials . </P>
where does action potential start in a neuron
where does action potential start in a neuron
the axon hillock
the axon hillock