(Solved) How can I grasp the understanding of an action potential in a nerve cell ?

Look at it this way are three groups of ion channels:
1. Voltage Gated: open in response to potential changes across the plasma membrane
2. Stretch Gated: open in response to mechanical/physical distortions of the plasma membrane
3. Ligand Gated: open in response to molecules binding to the channel protein

Also keep in mind that the permeability of a membrane to ions is strictly dependent on ion channels and active transport ion pumps, as charged ions are not able to cross the lipid bilayer.

Please not that a voltage gated channel cannot itself initiate and actional potential because it can not open by its self unless there is a potential change produced. This potential change is usually produced by either ligand gated channels, with neurotransmitter binding to them opening them and cause an influx of sodium into the cell or by stretch-gated channels, usually in sensory nerve endings which open in response to mechanical distortion of the plasma membrane.
Activation causes influx of sodium into the cell, this changes the membrane potential bringing it to THRESHOLD (minimum potential need to open a particular ion channel)
Usually when a sodium channel is open causing depolarization it closes in a few milliseconds, but allows enough sodium into the cell to open the neighboring sodium channel, but it itself enters into a "refractory" period, where the channel cannot be opened regardless of the magnitude of stimulus, this ensures a "one way valve" causing the action potential to propagate in only one direction and not in both direction.

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How can I grasp the understanding of an action potential in a nerve cell ?

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