The Action Potential

Action Potential

A rapid reversal of membrane potential where the inside becomes positively charged with respect to the outside for 2-3 msec

- neural code from frequency and pattern

Synaptic Transmission

The frequency and pattern of action potentials constitute the code used by neurons to transfer information from one location to another

zone of integration

initiated at axon hillock

zone of output

travels down axon to the presynaptic terminal

depolarization

membrane voltage becomes more positive

hyperpolarization

membrane voltage becomes more negative

Efflux

the flowing OUT of a particular substance or particle

Influx

a flowing or pouring IN; arrival IN massive numbers

-positive ion INFLUX

-negative ion EFFLUX

What influx/efflux results in depolarization?

-positive ion efflux

-negative ion influx

What influx/efflux results in hyperpolarization?

caused by depolarization of membrane beyond threshold

What is required for an action potential to generate?

-naturally via excitatory synaptic transmission

-artificially via current injection into a neuron with microelectrode

How does a depolarizing current occur?

Firing Frequency

reflects the magnitude of the depolarizing current:

-no depolarization=no action potential

- firing rate increase=depolarizing current increases

Neurons: electrically active - fire action potentials

Glia: electrically "silent" cells

Neurons vs. Glia- Electrical Properties

all-or-none principle

the law that the neuron either fires at 100% or not at all

chain reaction

A series of reactions in which the product or by-product of the reaction initiates further reaction.

Resting potential

The difference in electric charge between the inside and outside of a neuron's cell membrane

Rising Phase

The first part of an action potential, characterized by a rapid depolarization of the membrane.

-inward sodium current

Overshoot

the part of the action potential where the inside of the neuron is positively charged with respect to the outside

Falling phase

a rapid polarization until the inside of the membrane is actually more negative than the resting potential

-outward potassium current

undershoot

The part of an action potential when the membrane potential is more negative than at rest