Depolarization is a decrease in the potential difference in a cell in a state of physiological rest between its cytoplasm and extracellular fluid , that is, a decrease in the resting potential . There are two types of depolarization: passive depolarization and active depolarization.
Depolarization can be triggered by three stimuli without causing any harm to the cell. Such incentives include: mechanical, chemical and electrical [1] . One example of a mechanical stimulus may be temperature. High temperature leads to the expansion of the membrane , cold reduces it.
Depolarization that occurred in one place of the membrane serves as an incentive for the spread of depolarization across the membrane. Sodium ion, rushing into the cell at the place where the depolarization occurred and the sodium pump stopped acting, displaces the potassium ion. Sodium ions are smaller and more mobile than potassium ions. Therefore, more sodium ions enter the cell than potassium ions come out of it. As a result, the depolarization curve crosses the zero mark and rises above. The cell is again polarized, but with the opposite sign. At some point, the flare acquires an internal positive charge, due to the presence of an excess of sodium ions in it. A small negative charge appears on the outside of the membrane.
Passive Depolarization
Passive depolarization occurs when a weak electric current passes through the membrane in the outgoing direction (the anode is inside, the cathode is outside), which does not cause changes in the membrane ionic permeability.
Active depolarization
Active depolarization develops with an increase in the permeability of the membrane for Na + ions or with its decrease for K + ions. When an action potential arises, active depolarization associated with a transient increase in the sodium permeability of the membrane acquires a regenerative character: depolarization increases sodium permeability, which in turn leads to an increase in depolarization, etc. Long-term depolarization of the membrane leads to inactivation of the sodium channels and an increase in potassium permeability. , resulting in a drop or complete disappearance of cell excitability [2] .
Notes
- ↑ POLARIZATION AND DEPOLARIZATION . Murzim. Date of appeal April 14, 2019.
- ↑ Depolarization - Biological Dictionary . bioword.ru. Date of appeal April 14, 2019.