How does the neuron moves a resting place to firing and then back to resting state?

Answer 1

The event in which a neuron's membrane potential rapidly rises from its resting potential and then falls back to its resting potential is called an action potential.

The neuron fires an action potential and returns to its resting state in the following manner:

Initially the resting potential of the inside of the cell membrane of a neuron with respect to the outside is about -70mV (this condition is referred to as polarized).

As neural signals from inputs at the dendrites of the neuron move down the dendrites and across the soma (cell body), they arrive at the beginning of the axon, called the axon hillock; those signals are comprised of quantities of sodium ions which have been pushed to the axon hillock by an influx of sodium ions through ligand-gated sodium ion channels (ion pores which open from the action of a chemical messenger neurotransmitters in a receptor portion of the ion gate) in the dendrites which have been opened by neurotransmitters released by a pre-synaptic neuron diffusing across the synaptic cleft into receptors at the dendrite.

Firing: If enough quantity of sodium ions reach the axon hillock to raise the membrane potential at that point to a threshold value of about -55mV(the trigger voltage), this is sufficient to open voltage-gated sodium ion pores in the initial segment of the axon, which allows more sodium ions in, raising the membrane voltage to from 50mV to 100mV (called depolarization), which cause nearby v-gated Na ion pores to open, which lets in more sodium ions, which open successive v-gated ion pores along the length of the axon. This moving (action) potential (voltage) is the neural impulse.

Returning to resting state: during the peak of the action potential, when the membrane potential is at it greatest, sodium pores begin to close, and potassium pores are opened, and since there is more potassium inside the cell than outside, potassium ions begin to leave the neuron through those channels; with the loss of these positively charged ions, the membrane voltage becomes more and more negative, opening more potassium pores, until the membrane voltage actually undershoots the resting potential momentarily. At this point the potassium pores begin to close, and the membrane potential rises back to the resting potential.

(please see the links below for additional explanations)