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Hyperpolarization (biology) Hyperpolarization is a change in a cell's membrane potential that makes it more negative. It is the opposite of a depolarization. It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold. Hyperpolarization is often caused by efflux of K + (a ...
In biology, depolarization or hypopolarization[ 1 ][ 2 ] is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is essential to the function of many cells, communication between cells, and the overall physiology ...
As an action potential (nerve impulse) travels down an axonthere is a change in electric polarity across the membraneof the axon. In response to a signal from another neuron, sodium- (Na+) and potassium- (K+)–gated ion channelsopen and close as the membrane reaches its threshold potential. Na+channels open at the beginning of the action ...
An influx of sodium into the cell through open, voltage-gated sodium channels can depolarize the membrane past threshold and thus excite it while an efflux of potassium or influx of chloride can hyperpolarize the cell and thus inhibit threshold from being reached.
The rapid depolarization of the cell, during phase 0, causes the membrane potential to approach sodium's equilibrium potential (i.e. the membrane potential at which sodium is no longer drawn into or out of the cell). As the membrane potential becomes more positive, the sodium channels then close and lock, this is known as the "inactivated" state.
The potassium ion channels are slower-acting than the sodium ion channels and so as the membrane potential starts to peak, the potassium ion channels open and causes an outflux of potassium to counteract the influx of sodium. At the peak, the outflux of potassium equals the influx of sodium, and the membrane does not change polarity.
Electrotonic potentials which decrease the membrane potential are called inhibitory postsynaptic potentials (IPSPs). They hyperpolarize the membrane and make it harder for a cell to have an action potential. IPSPs are associated with Cl − entering the cell or K + leaving the cell. IPSPs can interact with EPSPs to "cancel out" their effect.
Excitatory post-synaptic potentials (EPSPs) depolarize the membrane and move the potential closer to the threshold for an action potential to be generated. Inhibitory postsynaptic potentials (IPSPs) hyperpolarize the membrane and move the potential farther away from the threshold, decreasing the likelihood of an action potential occurring. [2]