Chapter 19, Problem 90PP

Nerve cells and R-C circuits. The portion of a nerve cell that conducts signals is called an axon. Many of the electrical properties of axons are governed by ion channels, which are protein molecules that span the axon’s cell membrane. When open, each ion channel has a pore that is filled with fluid of low resistivity and connects the interior of the cell electrically to the medium outside the cell. In contrast, the lipid-rich cell membrane in which ion channels reside has very high resistivity

90. Cell membranes across a wide variety of organisms have a capacitance per unit area of 1 μF/cm². For the electrical signal in a nerve to propagate down the axon, the charge on the membrane “capacitor” must change. What time constant is required when the k>n channels are open?

1. A.    1 μs
2. B.     10 μs
3. C.     100 μs
4. D.    1 ms