hyperpolarisoida

Hyperpolarisoida is a Finnish verb meaning to make a cell's membrane potential more negative than its resting value; in English, to hyperpolarize. The term is used mainly in neuroscience and physiology to describe a state of increased negativity of the membrane potential.

Hyperpolarization reduces excitability by moving the membrane potential further from the threshold for triggering an action potential and by reducing the probability that depolarizing inputs will reach threshold. It also affects the temporal summation of inputs, often prolonging the refractory period after spikes.

Causes include increased potassium conductance, such as opening of voltage-gated or Ca2+-activated K+ channels, and chloride influx through GABA_A or glycine receptors when the chloride reversal potential is near or below resting. Sodium-potassium ATPase activity and afterhyperpolarization currents after spikes can contribute transiently as well. In mature neurons, inhibitory synaptic inputs that activate GABA_A receptors are a common source of hyperpolarization; in developing neurons, GABA can be depolarizing if chloride gradient is different.

Applications: In research, hyperpolarization is used to study neuronal circuits and plasticity. Tools such as optogenetic pumps (halorhodopsin) induce hyperpolarization with light, allowing selective inhibition of neurons. In physiology, hyperpolarization is a fundamental mechanism underlying inhibitory signaling in the nervous system and in cardiac tissue to regulate excitability.