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Motor innervation, motor unit organization and afferent innervation of m. extensor digitorum communis of the baboon's forearm
Author(s) -
Eccles Rosamond M.,
Phillips C. G.,
Chien-Ping Wu
Publication year - 1968
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1968.sp008600
Subject(s) - extensor digitorum communis , efferent , anatomy , nerve conduction velocity , chemistry , axon , afferent , motor nerve , stimulation , motor unit , biology , neuroscience , tendon
1. One hundred and fifty efferent axons innervating m. extensor digitorum communis (EDC) were isolated in filaments of C7 and C8 ventral roots of baboons. Conduction velocities were measured antidromically by stimulating the muscle nerve and recording from the filaments, and fell into two groups: a fast (49‐84 m/sec) and a slow (22‐41m/sec), presumably fusimotor group. The threshold for these latter axons exceeded the strength needed to elicit the maximal motor twitch. 2. Stimulation of ventral root filaments containing slow axons produced no contractile tension in EDC. 3. Stimulation of ventral root filaments containing fast‐group axons elicited all‐or‐nothing twitches of motor units of EDC. The twitch tensions of 66·3% of the units were < 2·0 g wt.; only 8·7% were > 5·0 g wt. Tetanus‐twitch ratios were 1·4‐4·7 in a sample of 14 units. Contraction times were between 15 and 35 msec in 97% of the units. There was no correlation between contractile properties and axonal conduction velocity. 4. Afferent volleys from the stimulated EDC nerve were recorded from C6 or C7 dorsal roots. The threshold was below the threshold for a just‐detectable motor twitch in ten out of eleven baboons. Conduction velocity of the earliest component of the muscle afferent volley was 67‐83 m/sec. 5. The conduction velocities of twenty‐eight spindle afferents, identified by their responses to linear stretches of EDC and by their unloading by maximal twitches, were all < 70 m/sec. Higher dynamic sensitivity tended to be associated with higher conduction velocity.