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ON THE TIME RELATIONS OF THE KNEE‐JERK AND SIMPLE REFLEXES
Author(s) -
Jolly W. A.
Publication year - 1911
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0370-2901
DOI - 10.1113/expphysiol.1911.sp000084
Subject(s) - reflex , reflex arc , anatomy , latency (audio) , jerk , ankle jerk reflex , microstimulation , neuroscience , medicine , physics , anesthesia , psychology , computer science , stimulation , telecommunications , classical mechanics , acceleration
A diphasic action current is recorded by means of the string galvanometer from the quadriceps muscle when the knee‐jerk is elicited. Its latency is about half as long as that of the electrical variation accompanying action of the muscles in the homonymous flexion reflex of the hind limb. The latency of the heteronymous extension reflex is about one‐thousandth of a second longer than that of the homonymous reflex. An electrical variation, consisting in a diminution of the demarcation current, is observed in the cut anterior crural (femoral) nerve when the skin on the dorsum pedis or mesial aspect of the thigh is mechanically stimulated. A similar electrical variation with shorter latent period is obtained in the same nerve when the knee‐jerk is elicited. By means of these variations the latency of afferent nerve endings can be determined, after deducting nerve conduction time from the latency of the variation. The synapse time in the case of the knee‐jerk and the other reflexes is obtained by deducting from the latency of the action current of the muscles reflexly excited periods attributable to (1) the afferent endings, (2) nerve conduction, and (3) motor endings and latency of action current. The action currents accompanying knee‐jerk and flexion reflex may in some cases be detected in the same recorded curve. The synapse time of the knee‐jerk in the spinal cat is about two‐thousandths of a second, of the homonymous flexion reflex about four‐thousandths. The relation between the synapse times suggests that the knee‐jerk mechanism involves one spinal synapse or set of synapses, while the flexion reflex involves two.