Limits of Variation of the Synaptic Delay of Motoneurons

THE MINIMAL duration of the synaptic delay of ocular motoneurons has been determined (1935a) with sufficient accuracy, but considerable dificulties have been found in measuring its maximal duration. Experimental results (1935d) indicated that the maximal delay is not much longer than the minimal delay, and that the expected small variations could scarcely be measured in the original preparation, in which the responses were recorded from the internal rectus muscle (1935d, p. 527). A sufficient degree of accuracy has now been attained by recording the responses from the trochlear nerve. Eccles (1936, 1937) has shown that the synaptic time in the superior cervical ganglion also is rigidly fixed within narrow limits, but it may be slightly shortened by creating facilitation or it may be lengthened by setting up refractoriness of the ganglion cells. Although in a different time scale, identical results are obtained with the trochlear motoneurons.