Electric Current and Cell Membranes
Thus far in our study of electricity, we have essentially confined our attention to electrostatics, or the study of stationary charges. Here and in the next three chapters we show some of the new phenomena that arise when charges move. We begin this chapter by generalizing our discussion to allow the flow of electric charges, known as an electric current, and we give a semiempirical derivation of Ohm’s law. Electrical measurement methods and devices are described as an application of Ohm’s law. More realistic models for a capacitor are then developed in a continued study of cell membranes in which electric charge can passively leak across the membrane. We give an overview of nerve structure and functioning and the spatial and temporal properties of the neuron membrane potential are detailed for both the quiescent and active states. The chapter concludes with a discussion of the electrical properties of individual ion channels as the underlying basis for membrane currents.