Ch. 4 Action Potentials

Graded potential

variable in strength and used for short-distance communication

Amplitude of graded potential

directly proportional to the strength of the triggering event (stimulus)

Local current flow

wave of depolarization that moves through the cell

How do graded potentials lose strength?

via current leak and cytoplasmic resistance

Axon hillock

spike-initiation zone

Depolarizations

excitatory

Hyperpolarization

inhibitory

Trigger-zone contains

lots of voltage-gated channels

Action potentials are …

are rapid reversals of membrane potential and are caused by depolarization of membrane beyond threshold

Phases of AP

depolarization, repolarization, and hyperpolarization

When the V_m depolarizes beyond the threshold level …

action potentials are generated

Firing frequency

reflects magnitude of the depolarizing current. the AP firing rate increases as the depolarizing current increases

Max firing frequency

1000 Hz

Absolute refractory period

after AP generated, a second one cannot be initiated for 1 msec.

Relative refractory period

follows the absolute refractory period, where a greater than normal stimuli is required to initiate a second AP