help with physiolab 9.0

Stages of an action potential:
1. depolarising stimulus reaches threshold at which voltage-gated sodium channels open
2. rapid sodium influx through voltage-gated sodium channels - rising phase
3. potassium efflux through voltage-gated potassium channels and inactivation of (voltage-gated) sodium channels - falling phase

Potassium flow out of the cell eventually leads to a negative membrane potential and undershoot. Action potentials cannot occur in this phase (the refractory period) because sodium channels are inactivated.

The sodium channels are deinactivated once the membrane potential becomes sufficiently negative (because they are voltage gated). If there is still a depolarising stimulus about (from a microelectrode or neurotransmitter), this means that the sodium channels can now open and allow sodium influx again, causing another action potential.

The firing rate is determined by the magnitude of the depolarising stimulus, up to a point. After an action potential, it is impossible to generate another for about 1 msec due to the inactivation of sodium channels. The maximum firing frequency is around 1000Hz