جهد الفعل
Action potentials travel faster in a larger axon than a smaller one, and squid have evolved the giant axon to improve the speed of their escape response. The increased radius of the squid axon decreases the internal resistance of the axon, as resistance is inversely proportional to the cross sectional area of the object. This increases the space constant (formula_1), leading to faster local depolarization and a faster action potential conduction (formula_2).