Chapter 26, Problem 26.87PP

In a simple model of an axon conducting a nerve signal, ions move across the cell membrane through open ion channels, which act as purely resistive elements. If a typical current density (current per unit cross-sectional area) in the cell membrane is 5 mA/cm² when the voltage across the membrane (the action potential) is 50 mV, what is the number density of open ion channels in the membrane? (a) 1/cm²; (b) 10/cm²; (c) 10/mm²; (d) 100/µm².