depolarisatsiooni

Depolarisation is the process by which a system that is normally polarized loses or reduces its polarity. In biology, it most commonly refers to changes in the electric potential across a cell membrane, shifting the balance of charge between the inside and outside of the cell.

In neurons and muscle cells, the resting membrane potential is typically around −70 millivolts (mV). When a stimulus causes the membrane potential to rise toward zero, voltage-gated sodium channels open, allowing Na+ to enter the cell. If the depolarisation reaches a threshold (about −55 mV), an action potential is triggered, and the membrane potential rapidly rises to roughly +30 mV (upstroke). Repolarisation follows as Na+ channels inactivate and K+ channels open, returning the potential toward the resting level, often with a brief hyperpolarisation before stabilisation.

Depolarisation is essential for nerve signaling and muscle contraction. The timing and magnitude of the depolarisation determine whether membranes fire action potentials. Abnormal depolarisation—such as sustained depolarisation due to electrolyte imbalance, ischemia, or toxins—can disrupt signaling and contribute to pathologies like seizures or cardiac arrhythmias.

In other domains, depolarisation describes a general loss of polarization in materials science and optics. For example, in dielectrics or ferroelectric materials, spontaneous polarization can be reduced or reversed when temperature rises above a transition point or when external conditions remove the polarization. In optics, depolarisation refers to changes in the polarization state of light caused by scattering or anisotropic media.

Overall, depolarisation denotes the shift from a polarized to a less polarized state, with implications across biology, physics, and materials science.