Action potential conduction

In a nerve process or skeletal muscle fiber, the spread of activity is essentially only in one dimension, along the fiber. However, in smooth muscle the situation is rather more complex geometrically, and all three dimensions are involved. Action potentials conduct electrotonically just as they do in nerve fibers but they do so in three dimensions. In situ, regions supporting action potentials are not pointlike but tend to be large and the spread from them is more like a surface, approximating a plane. 

A second factor that influences the velocity of action potential conduction is the diameter of the axon. The greater the diameter is then, the lower the resistance to current flow along the axon. Therefore, the impulse is... 

The mechanism of 4-aminopyridine toxicity is due to the direct actions of the compound as a blocker of voltage-sensitive K" " channels. At toxic doses, the chemical disrupts normal action potential conduction and nonselectively enhances neurotransmitter release. Because 4-aminopyridine blocks voltage-sensitive K+ channels on neurons, it has the capacity to enhance action potential conduction in demyelinated tissue with therapeutically beneficial results. Toward this end, a compound (fampridine) is in development... 

Fig. 2. Diagrammatic representation of oscilloscope tracing of typical action potential. Conductance (G) changes for particular ions are shown as a function of time. Equilibrium potentials for Na+ and K+ (ENa+ 4 f K+) are also depicted.

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