Depolarization

The Depolarization of a cell, indicates the transitory passage of the potential of membrane of a negative value, known as of rest, towards a positive value. One speaks about depolarization in particular for the cells excitables (Neuron, muscular Cellule…) from the physiological implication of the variations of membrane potential in the operation of the Nervous system. In a general way, any cell is dépolarisable, although physiologically, only the Neuron S, the muscular cells and the cells of certain glands are depolarized in their physiological environment.

The membrane potential depends inter alia extracellular and intracellular concentrations on both sides on the membrane on the ionic types for which the cell is permeable (calcium, potassium, sodium, chlorine). It is necessary to refer to the equation of Goldman-Hodgkin-Katz in voltage: a variation of extra and/or intracellular ionic concentrations will induce a variation of the potential of membrane. In the same way, a modification of the permeability of the membrane (in particular by an opening or closing of ionic channels) will influence it. In both cases, plus a membrane is permeable with a given ionic type, plus a change related to this ion (i.e. a variation of ionic concentration, an opening/closing of channels) will modify the value of the membrane potential.

Example

Let us take a simple example: Under physiological conditions, the neurons (cell excitable) but also the cells gliales (cell not excitable) are strongly, but not exclusively, permeable with potassium. An increase, even light, of extracellular potassium will depolarize them (to be deepened) -->. Another example is the post-synaptic generation of potential at the time of the neuronal transmission. The release of neuro-transmitters in the synapse will induce the opening of ionic channels: ionic currents will be generated, which will modify the concentrations ionic intracellular and extracellular (by the entry and the exit of ions), and while opening, the ionic channels will increase the permeability of the membrane. One in the case of speaks about exiting post-synaptic potential a neuronal depolarization.

It should be noted that for a precise ionic type, its influence on the potential of membrane of a cell (it will induce a depolarization, a hyperpolarisation) will depend on the potential of balance of this ion (to be approdondir) -->.

See too

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