An action potential is the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell

An action potential is the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell. An action potential occurs when a neuron sends information down an axon, away from the cell body. A threshold is the minimum amount of stimulation needed to start a neural impulse. Action potentials generated by neural impulses are “all or nothing”. Meaning the signal reaches the threshold for communication or it doesn’t. No signal is stronger or weaker than another. Depolarization increase in positive charge inside the plasma membrane caused by a depolarizing graded potential causes increasing numbers of voltage gated Na+ channels to open rapidly.
The equilibrium potential for potassium is negative so it wants the charge across the membrane to be negative so by all of these potassium ions leaving that makes the membrane potential more negative which is called repolarization, now hyperpolarization exists following each action potential. The potential exists because the voltage-gated k+ channels open and close more slowly than the voltage-gated Na+ channels and remains open for a slightly longer time than it takes to bring the membrane potential back to its resting levels.
Now let’s talk about the refractory period because once an action potential is produced at a given point on the plasma membrane the sensitivity of that area to further stimulation decreases for a time called no other than the “refractory period.” The absolute refractory period places a limit on the rate at which a neuron can conduct impulses and the relative refractory period permits variation in the rate at which a neuron conducts its impulses.
Furthermore, a subthreshold is any stimulus not strong enough to produce a graded potential and what that means is that A small deviation from the RMP that makes the membrane either more polarized (more negative inside) or less polarized (less negative inside). Graded potentials can either be Hyperpolarizing or Depolarizing events, Depolarizing brings it closer to zero or higher, Hyperpolarizing makes it more negative. This Occurs in response to the opening of a mechanically-gated or ligand-gated ion channel (found on cell body and dendrites of a neuron) If the membrane is more negative, it’s harder to stimulate and depolarize it. There for no action potential is produced. Now a threshold stimulus produces a graded potential that is just strong enough to reach threshold and cause the production of a single action potential.