hyperpolarizes

Hyperpolarization refers to a change in the membrane potential of a cell toward a more negative value than its resting potential. In neurons, this makes the cell less likely to fire an action potential. The most common mechanisms are the opening of potassium channels, which allows K+ to leave the cell and increases the negative charge inside, and the opening of chloride channels (for example, via GABA_A or glycine receptors), permitting Cl- to enter. Other processes, such as prolonged activation of ion pumps, can also contribute to a hyperpolarized state. GABA_A receptor activation hyperpolarizes neurons by increasing Cl- conductance.

In neural signaling, hyperpolarization serves as a major form of synaptic inhibition, reducing excitability and suppressing action potential generation. It helps shape the timing of spikes, controls the integration of synaptic inputs, and contributes to the stabilization and rhythmicity of neural circuits. The effect of inhibitory signals can vary with development and cell type; for instance, in mature neurons GABA_A-mediated chloride influx typically hyperpolarizes the membrane, whereas in immature neurons higher intracellular chloride can render GABAergic input less inhibitory or even excitatory.

Beyond the central nervous system, hyperpolarization occurs in other excitable cells as well. In cardiac myocytes, afterhyperpolarization following an action potential contributes to the refractory period and helps regulate heart rhythm. In sensory systems, hyperpolarizing processes modulate transmitter release and signal encoding, enabling dynamic responses to stimuli. Overall, hyperpolarization is a fundamental mechanism for controlling cellular excitability and timing across tissues.

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