Depolarization

Usage of the term "depolarization" in biology differs from its use in physics, where it refers to situations in which any form of polarity ( i.e. the presence of any electrical charge, whether positive or negative) changes to a value of zero.

The sodium potassium pump is largely responsible for the optimization of conditions on both the interior and the exterior of the cell for depolarization.

This not only prevents the diffusion of ions pumped across the membrane but also involves the activity of potassium leak channels, allowing a controlled passive efflux of potassium ions, which contributes to the establishment of the negative resting potential.

While the sodium–potassium pump continues to work, the voltage-gated sodium and calcium channels[7] that had been closed while the cell was at resting potential are opened in response to an initial change in voltage.

[8] Sodium channels possess an inherent inactivation mechanism that prompts rapid reclosure, even as the membrane remains depolarized.

Once the cell's interior is sufficiently positively charged, depolarization concludes, and the channels close once more.

The increased positive charge within the cell now causes the potassium channels to open.

The hyperpolarization following an inhibitory stimulus causes a further decrease in voltage within the neuron below the resting potential.

By hyperpolarizing a neuron, an inhibitory stimulus results in a greater negative charge that must be overcome for depolarization to occur.

Regardless of it being excitatory or inhibitory, the stimulus travels down the dendrites of a neuron to the cell body for integration.

The stimuli that have traveled down the dendrites converge at the axon hillock, where they are summed to determine the neuronal response.

The ion channels allow calcium and sodium to pass freely into the cell, maintaining the depolarized state.

When these channels close, the rod cells produce fewer neurotransmitters, which is perceived by the brain as an increase in light.

[11][page needed] Endothelium is a thin layer of simple squamous epithelial cells that line the interior of both blood and lymph vessels.

This plasticity in the structural strength of the vascular endothelium is essential to overall function of the cardiovascular system.

Endothelial cells accomplish these feats by using depolarization to alter their structural strength.