Neurons

Resting potential

(-70mV) membrane potential is constant, and low

Threshold potential

(-55mV) once membrane potential reaches this threshold, it shoots up and starts the refractory period

• Once reached, the neuron depolarizes, then repolarizes, returning to resting potential

Absolute refractory period

membrane potential increases, then falls

• Sodium channels open and then close, and are inactivated.

• Potassium channels open

• Determines maximum frequency in which action potentials can be fired

• Another stimulus cannot generate another action potential no matter how powerful the stimulus, because voltage-gated sodium channels are inactivated 

Relative refractory period

when the membrane potential falls below resting potential

• Sodium channels are reset to original state and Potassium channels begin to close

• Hyperpolarization – the change in membrane potential from resting potential to the lowest point of membrane potential

• * relative refractory period can be overcome – an action potential CAN occur if the impulse is strong enough

Hyperpolarization

the change in membrane potential from resting potential to the lowest point of membrane potential