Assume that a typical open ion channel spanning an axon’s membrane has a resistance of 1 × 10¹¹ Ω. We can model this ion channel, with its pore, as a 12-nm-long cylinder of radius 0.3 nm. What is the resistivity of the fluid in the pore?

(a) 10 Ω ∙ m;
(b) 6 Ω ∙ m;

(c) 2 Ω ∙ m;

(d) 1 Ω ∙ m.

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.