Meeting Abstract
101.11 Thursday, Jan. 7 Tradeoffs in responsiveness and resolution in the peripheral nervous system MORE, HL*; HUTCHINSON, JR; COLLINS, DF; WEBER, DJ; AUNG, SKH; CHEN, J; BEG, MF; DONELAN, JM; Simon Fraser University, Burnaby, BC; The Royal Veterinary College, London, UK; University of Alberta, Edmonton; University of Pittsburgh, PA; University of Alberta, Edmonton; Simon Fraser University, Burnaby, BC; Simon Fraser University, Burnaby, BC; Simon Fraser University, Burnaby, BC hmore@sfu.ca
In order to investigate the physiological mechanisms used by small and large animals to coordinate their movements, we examined the effect of animal size on axon size, number, and conduction velocity. The time it takes an animal to sense and respond to stimuli (responsiveness) depends on axon diameter, and the ability of an animal to distinguish between sensory stimuli and generate graded muscle forces (resolution) depends on the number of axons per unit volume. Since nerve cross-sectional area depends on both these factors we hypothesized that, particularly in larger animals, there is a tradeoff between responsiveness and resolution in order to maintain nerve size within reasonable limits. To test our hypothesis, we used new electrophysiological experiments to determine maximum axonal conduction velocity in the sciatic nerves of the least shrew (Cryptotis parva) and Asian elephant (Elephas maximus), and combined these values with existing data for nine animals of intermediate size. We also used histological techniques and scanning electron microscopy to acquire and analyze images of shrew and elephant nerves. Our analysis demonstrated both that conduction velocity was nearly constant and that total axon number increased approximately with the cube root of mass over a 100-fold increase in leg length. These relationships result in longer delays and a decreased ability to precisely sense stimuli and control movement in larger animals, which may require larger animals to rely more on prediction to control movement and respond to their environment.
