graded potential

A graded potential is a small, local change in the electrical charge across a neuron's outer skin (its membrane) whose size matches the size of whatever poked the cell. A gentle nudge makes a tiny voltage bump; a stronger nudge makes a bigger one. Think of it like a dimmer switch rather than an on/off light switch: the brightness slides smoothly up and down with how hard you turn the knob. This is different from the neuron's all-or-nothing signal — the action potential, the brief electrical spike that fires at full strength or not at all.

These ripples usually start where a neuron receives input, such as at a connection from another cell (a synapse) or at a sensory ending that feels touch or light. An incoming signal briefly opens tiny gated pores in the membrane (ion channels), letting charged particles flow in or out and tilting the local voltage up or down. But a graded potential fades as it spreads, growing weaker the farther it travels from where it began, like a splash in a pond that flattens into stillness. Its job is to add things up: many small graded potentials arriving close together can pile on top of one another, and if their combined push reaches a tipping point at the neuron's launch zone, they trigger a full action potential that races down the cell to pass the message along.