The Song of the Cell: An Exploration of Medicine and the New Human

by Siddhartha Mukherjee

What is that “stimulus”? It’s the movement of ions—principally calcium—in and out of cells through specialized channels on the membranes of heart cells. In its resting state, the heart cell has low levels of calcium. When it is stimulated to contract, calcium floods into a heart cell, and it instigates contraction. And calcium’s entry is a self-feeding loop: the entry of calcium releases more calcium from the heart cell, resulting in a sharp, steep spike in calcium levels. The interconnections between the cells—those “junctions” that were identified in the 1950s—carry the ionic message from cell to cell. The one becomes the many. Crowds generate power. The organ—a continuum of cells—thus behaves as a whole.