A neuron listens to the electric world like a sensitive microphone. Its 'ears' are ion channels in the membrane: they open in response to voltage, created by the flow of charged particles. But interference is inevitable in this flow. First, shot noise makes itself known: each ion, darting through a channel, delivers a microscopic thump, like a rare raindrop on a tin roof. For a single channel, this limits accuracy to about 10 millivolts.

When the signal is gathered from hundreds of channels, the shot impacts average out, but another menace emerges — thermal noise, the incessant trembling of molecules driven by heat. This background hum never fades and sets the ultimate limit on the neuron’s sensitivity. It’s striking that the transition from one noise to the next occurs precisely at the channel densities observed in real neurons. In the axon hillock, where speed is vital, there are hundreds of times more channels than on the cell body — nature economizes resources, operating on the razor’s edge of physical laws.