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Single‐fiber EMG study of the flexor carpi radialis H reflex
Author(s) -
Jabre Joe F.,
Stålberg Erik V.
Publication year - 1989
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880120702
Subject(s) - jitter , reflex , electromyography , stimulus (psychology) , stretch reflex , latency (audio) , h reflex , neuroscience , anatomy , psychology , medicine , computer science , telecommunications , psychotherapist
Late responses were studied in the flexor carpi radialis muscle by surface‐recording and single‐fiber electromyography. By single‐fiber studies we were able to distinguish 2 distinct components. One was an H reflex obtained without a preceding M response and with a stimulus response jitter of about 100 μsec; its latency was shortened and jitter decreased with the Jendrassik maneuver. The other was an F wave always preceded by an M response and with a stimulus response jitter of under 50 μsec; its jitter and latency are unaffected by the Jendrassik maneuver. At the single‐fiber level it was possible to determine the rate of occurrence of individual H reflexes and F responses for a given number of surface‐applied stimuli. The H reflex had a very high rate of occurrence (up to 97%), whereas the F wave occurred very infrequently (less than 2% of the time). Using the H reflex rate of occurrence in conjunction with the maximal surface H/M amplitude ratios allowed us to determine the proportion of alpha motor neurons which participate in the H‐reflex generation. The study of H‐reflex jitter gives an estimate of the central synaptic jitter and effectiveness of the spatial and temporal summation of type 1a fiber inputs on the motor neurons.