A model of the differing change in motor and sensory action potentials over distance

Clinically recorded motor and sensory nerve responses show different degrees of change in response size over distance along a nerve. We describe a computer model to investigate possible causes of this phenomenon. Effects of the range of conduction velocity in a nerve and the size of the constituent action potentials forming the recorded response are evaluated. We conclude that the broader duration of the motor unit potential is the predominant factor in accounting for motor nerve responses showing less change over distance than sensory responses. The contributions of temporal dispersion and phase cancellation are also discussed.