Single-fiber EMG study of the flexor carpi radialis H reflex.
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 musec; 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 musec; 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.
Department of Neurology, VA Outpatient Clinic, Boston University, Massachusetts 02130.
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JF
Jabre
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Stålberg
D000293:Adolescent; D000328:Adult; D004576:Electromyography; D005260:Female; D005542:Forearm; D006181:H-Reflex; D006801:Humans; D008297:Male; D008875:Middle Aged; D009132:Muscles / Q000294:innervation*; D012023:Reflex, Monosynaptic