Neurology Edited by Professor Emeritus Desire' Dubounet, IMUNE

fibers. Sequential action potentials can then be detected by a surface electrode.This is how the variances in nerve conduction velocity were found by Erlanger andGasser (1937). Their Nobel Prize-winning study and experiments with somesample oscillograms are classic. The investigators employed injured tissue toobtain unit activity. They proved that the propagation velocity in nerve is related tofiber diameter. Erlanger and Gasser demonstrated that the wave form of the actionpotential recorded by a surface electrode placed on a mixed nerve trunk, in which allof the axons are stimulated simultaneously, will depend on the propagationvelocities and the distance from the point of stimulation to the active (surface)electrode. The electrode can detect the action potentials of the fibers below it.Electrodes in the more distant fibers will contribute less to the recorded actionpotential. Fig5Transmembrane potential and current changes in the giant barnacle muscle inresponse to square-wave stimuli. The graded response to an increase in stimulusintensity is shown at C; local spike formations produced by first decreasing theintracellular concentration of calcium and then varying the extracellular calciumconcentration (20, 84, 338 mM)The action potentials of a nerve trunk containing a population of fibers havingdifferent diameters and therefore different propagation velocities: (a) recordingmethod; (b) action potentials from the fastest propagating fibers (AY, , ), (c) actionpotentials B and C from the fibers with slower propagation velocity.Action potentials of a mixed nerve recorded with a pair of surface electrodesduring physiological activation of its neurones (or receptors) will reflect theasynchrony of activation of the axons. Also reflected are differences in theirpropagation velocities, and the electrode separation. Action potentials have asimilar asynchrony as the activity of skeletal muscle is recorded. Here wedemonstrate skeletal muscle where there is a spatial distribution of motor endplates. If all the axons were excited simultaneously by a single stimulus, all themuscle fibers would not be excited simultaneously. An electrode close to the end ofthe muscle will detect the action potentials of the individual fibers as they arrive atvarious times because of the distances from the end plates. Action potentialrecorded will be polyphasic. If motor neurones are activated physiologically,9