This article discusses the biology and physics of electrical system of living body that controls all body functions. Electrochemical potentials in the nerve cells are the source of billions of electrical signals, which propagate from all parts of body to the brain via neurotransmitters in the living body whose measurements allow obtaining useful clinical information. The propagation of electrical pulses in the living body is like transmission of pulses in a cable. The living cell membrane offers resistance and capacitance that form a complex net of electrical circuit. The ratio of space constant between cells to the time constant of neural resistance and capacitance define the speed of nerve impulses from one cell to other cell.