Answer
The main factors that influence the speed of propagation of an action potential are diameter of nerve fiber, myelination, and temperature.
Work Step by Step
Nerve impulses travel faster along larger nerve fibers (fibers with greater diameters) than along nerve fibers with smaller diameters. An increase in axon diameter reduces the longitudinal resistance of the axon interior; it gives the current access to a greater number of parallel paths along which to progress.
Myelination also has a great effect on the speed of action potential propagation.The myelin sheath increases membrane electrical resistance, and prevents leakage of current across the plasma membrane. This forces the current to travel down the middle of the axon and to set up a new AP at each Node of Ranvier. This so-called saltatory impulse conduction significantly increases the speed of impulse propagation. In small unmyelinated nerve fibers conduction speed may be as low as 1m/sec; however, myelination can increase nerve conduction speed by factors of 15 to 250.
Temperature is also a factor that affects the rate of propagation of action potentials. The opening and closing of ion channels are influenced by enzyme activity. Since temperature affects the speed of enzyme activity ( e.g. in the Na+/K+ATPase pump) it has an effect on the rates of influx and efflux of Na+ and K+ through ion channels. Nerve impulse propagation is faster at higher temperatures, and slower at lower temperature-- within definite ranges.
