Depolarization

As depolarization ( also depolarization ) is called in neurology, a change in membrane potential toward positive (or less negative ) values ​​.

Properties

The cell membrane of nerve cells has ion pumps continuously provide for unequal distribution of the ions to the outside of the cell membrane as compared to the inside. In addition, the cell membrane is semi-permeable, so different permeable to different ions. Due to the unequal distribution of ions creates an electric membrane potential at rest and resting potential (about - 70 mV) is called.

Routing a signal within a nerve cell is based on the influx of ions after activation of the nerve cell. Intracellular prevails an excess of negative ions, the cell membrane is polar ( negative inside than on the outside, negative potential difference ). Streams now positive ions, reduces the polarity, because the ratio of positive and negative ions is balanced, the cell depolarizes. The Ioneneinstrom lead to compensation of the existing unequal distribution by diffusion, which results in a reduction of the amount of the membrane potential toward the reversal potential or in the direction of the chemical equilibrium. This is due to the charge redistribution by the incoming ions at the cell membrane briefly to positive potential values ​​, where the name originates depolarization. The opposite of the depolarization is a hyper- polarization. A restoration of the resting membrane potential after previous depolarization is called repolarization. The electrochemical driving force is proportional to the difference of resting potential and Aktionspotenzal.

In electrically excitable cells such as nerve cells may be over- or subliminal depolarization. Threshold as the threshold potential for the opening of voltage activated sodium ion channels (sometimes calcium ion channels ) designated in this case. This is voltage-gated sodium ion channels typically at -50 mV. Above this value, open the sodium channels, which amplifies the depolarization and an action potential triggers. If the depolarization below the threshold, the membrane potential returns to the resting value without overshoot. The dualism of the effects produced is described in all-or -nothing law.

The term depolarization is independent of the cause ( passively or actively by altering the properties of the membrane ) and the event ( action potential Postsynaptic potential excitable cells of plants, etc.).

Of particular importance is a depolarization in electrically excitable cells.

For example, the resting membrane potential amounts to -70 mV. A change of 30 mV to -40 mV depolarization. Thereafter, when the resting membrane potential of -70 mV reached again, it is called repolarization. A decrease by 20 mV to -90 mV hyperpolarization.