What causes the hyperpolarization and depolarization of membrane potential, and how does change in membrane potential trigger graded and action potentials for the transmission of signals?

Hyperpolarization is a change in a cell's membrane  potential that makes it more negative.

Depolarization s a change within a cell, during which the cell undergoes a shift in electric charge distribution.

Explanation:

The hyperpolarization inhibits action potential by increasing the stimulus required to move the membrane potential to the action potential threshold. Voltage gated ion channels respond to changes in the mebrane potential.

The duration of hyperpolarization is the limiting factor in the rate at wich action potentials  can be initiated.

Hyperpolarization is caused by a delay in the inactivation of Na+ channels.

Depolarization is caused by the opening of Na+ channels making the membrane potential more positive.

Changes in membrane potential making it more positive will trigger a potential action if the membrane potential is big enough to open a big number of ion channels. If the change in membrane potential is not big enough a small number of ion channels will open and the potential action will travel short distances.

Explanation:

When the membrane potential increase from -90 mv to -55 mv Na+ channels open their gates and Na+ goes to the inside of the neuron, this process is called membrane depolarization, Na+ will go to the inside of the cell increasing the membrane potencial and opening more Na+ channels. When the potential action reaches +40 mv a potential action occurs. Shortly after this happens the Na+ channels will start to close their gates and the K+ channels will open their gates making K+ ions to rush out of the cell. K+ channels delay the closure of their gates causing an hyperpolarization due to the fact that the membrane potential is more negative than -90mv because of the great number of K+ that rushed out.

Graded potentials are triggered by small changes in membrane potential, they will not give potential actions. Potential actions depolarize all the membrane because they reached the +40mv membrane potential resulting in the activation of a large number of Na+ channels and transmitting the signal globally. Graded potentials will not produce the depolarization of the whole membrane only of a region transmitting a signal locally  because the membrane potential was not high enough to open all the Na+ channels but only local Na+ channels.

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