Unexpected life lessons from cardiac anatomy and physiology.

摘要

Cardiac tissues are a curious mixture of nerve and muscle fibres, a fusion of electrical anticipation and muscular release. Their surfaces contain molecular clocks that keep time by shuffling charged particles of calcium, potassium, and sodium across their cell membranes. Ion by ion, the electrical potential accumulates, as millions and billions and then trillions of ions gather. Then, suddenly, one more particle is simply too many, and a point of no return is reached. The electromagnetic pressure is too great. The gates are thrown open and suddenly let the ions all crash back in, causing an electrical current to fire across the myocardium. Systole has begun, as the individual fibre and then the entire heart contracts.