Template · placeholder prose

The spark

This page is a template for the owner's essays. The prose is placeholder; the figures are real simulations. Each figure keeps its own clock, pauses when it scrolls out of view, and can be played or paused on its own.

Heart muscle cells sit end to end, joined by tiny channels. When one cell fires, current leaks into its neighbour and lifts it past its threshold, so the neighbour fires too. Below, a strand of simulated cells is stimulated at its left end once a second. Watch the probe cell: its voltage jumps, holds a plateau, and only then falls back.

While a cell holds its plateau it cannot fire again. Try clicking the strand just behind a travelling wave: nothing happens there, because those cells are still refractory.

In a sheet of tissue the same rule produces richer shapes. If a wave is broken, its free end has nowhere to go but around, and it curls into a spiral that keeps rotating on its own.

The spiral's period, not any pacemaker, now sets how often each patch of tissue fires. That is one way a heart can be driven far faster than its own clock.