Action potentials (nerve impulses) are changes in the membrane potential that, once started, will affect the entire excitable membrane. The first action potential is usually generated at the initial segment of the neuron's axon. This activity will test your understanding of the sequence of events that occur at the membrane of the initial segment of the axon during generation of an action potential.

a..Threshold stimulus
Na+ channels open

b..Na+ influx
Depolarization

c.Na+ channels close

d..K+ efflux
Repolarization

e.Hyperpolarization
K+ channels close

Depolarization: Starts when a threshold stimulus applied on a neuron via Na+ mechanically operated channels that trigger action potential
Depolarization of membrane potential is due to influx of Na+ via voltage gated Na+ channels
Fast opening of voltage gated Na+ channels shift membrane potential from -70mV to +50mV at which voltage gated Na+ channels becomes inactive, thus influx of Na+ abruptly stops
Repolarization: Starts with the efflux of K+ by the opening of voltage gated K+ channels
Voltage gated K+ channels starts to open when voltage gated Na+ channels becomes inactive
Hyperpolarization: Occurs due to excessive efflux of K+ by voltage gated K+ channels
Additional efflux of K+ occurs due to slow inactivation of voltage gated K+ channels
In a typical neuron cell, membrane potential of cytoplasm is negative (-70mV) at rest hence called resting membrane potential
Resting membrane potential of excitable cells is established by Na+ K+ pump and maintained by K+ leaky channels at rest