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Depolarization

 
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In biology, depolarization is a decrease in the absolute value
Absolute value

In mathematics, the absolute value of a real number is its numerical value without regard to its Negative and non-negative numbers. So, for example, 3 is the absolute value of both 3 and -3....
 of a cell's membrane potential
Membrane potential

Membrane potential , is the voltage difference between the interior and exterior of a cell. Because the fluid inside and outside a cell is highly conductive, whereas a cell's plasma membrane is highly resistive, the voltage change in moving from a point outside to a point inside occurs largely within the narrow width of the membrane itself...
. Thus, changes in membrane voltage in which the membrane potential becomes less positive or less negative are both depolarizations. In neurons and some other cells, a depolarization large enough may result in an action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
. Hyperpolarization
Hyperpolarization (biology)

Hyperpolarization is any change in a cell membrane potential that makes it more polarized. That is, hyperpolarization is an increase in the absolute value of a cell's membrane potential....
 is the opposite of depolarization, and inhibits the rise of an action potential. The rising and falling phases of such an action potential are often imprecisely also called depolarization and hyperpolarization, respectively.

larization is often caused by influx of cations, e.g.






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In biology, depolarization is a decrease in the absolute value
Absolute value

In mathematics, the absolute value of a real number is its numerical value without regard to its Negative and non-negative numbers. So, for example, 3 is the absolute value of both 3 and -3....
 of a cell's membrane potential
Membrane potential

Membrane potential , is the voltage difference between the interior and exterior of a cell. Because the fluid inside and outside a cell is highly conductive, whereas a cell's plasma membrane is highly resistive, the voltage change in moving from a point outside to a point inside occurs largely within the narrow width of the membrane itself...
. Thus, changes in membrane voltage in which the membrane potential becomes less positive or less negative are both depolarizations. In neurons and some other cells, a depolarization large enough may result in an action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
. Hyperpolarization
Hyperpolarization (biology)

Hyperpolarization is any change in a cell membrane potential that makes it more polarized. That is, hyperpolarization is an increase in the absolute value of a cell's membrane potential....
 is the opposite of depolarization, and inhibits the rise of an action potential. The rising and falling phases of such an action potential are often imprecisely also called depolarization and hyperpolarization, respectively.

Mechanism

Depolarization is often caused by influx of cations, e.g. Na+
Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
 through Na+ channels, or by influx of Ca2+
Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
 through Ca2+ channels
Calcium channel

A Calcium channel is an ion channel which displays selective permeabiltiy to calcium ions. It is sometimes synonymous as voltage-dependent calcium channel, although there are also ligand-gated calcium channels....
.

On the other hand, outflux of K+
Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
 through K+ channels
Potassium channel

In the field of cell biology, potassium channels are the most widely distributed type of ion channel and are found in virtually all living organisms....
 inhibits depolarization.

If a cell has a resting potential of -70mV and the membrane potential changes to -50mV, then the cell has been depolarized.

Depolarization block

There are drugs, called depolarization blocking agents
Neuromuscular-blocking drugs

Neuromuscular-blocking drugs block neuromuscular transmission at the neuromuscular junction, causing paralysis of the affected skeletal muscles....
, that inhibit depolarization, e.g. by blocking the channels responsible for depolarization, or by opening K+ channels. Examples include the nicotinic agonist
Nicotinic agonist

A nicotinic agonist is a drug which enhances the action at the nicotinic acetylcholine receptor .Examples include:* nicotine * acetylcholine, the endogenous agonist of nAChRs...
s suxamethonium and decamethonium
Decamethonium

Decamethonium bromide is a depolarizing muscle relaxant or neuromuscular blocking agent, and is used in anesthesia to induce paralytic....
.

External links

  • - online textbook by Purves, et al
  • Molecular, Cellular, and Medical Aspects by Siegel, et al