Journeys: Heart. Stop 3

Heart muscle

Zooming in a hundred times. The heart wall is made of tiny thread-like cells. Touch the yellow knot at the top!

This knot is like the heart's switch. It sends an electric signal all by itself, and the cells squeeze.

The cells hold on to each other, so the signal runs through the whole heart. This is real heart muscle.

The switch works by itself, even while you sleep. Doctors record its signals on a cardiogram, spike by spike.