Relation between nerve axon size and muscle unit size and speed in motor units of cat hind limb muscles
Gerlach, R.L.; Stauffer, E.K.; Goslow, G.E.; Stuart, D.G.
Electromyography and Clinical Neurophysiology 16(2-3): 177-190
1976
ISSN/ISBN: 0301-150X PMID: 964197 Document Number: 109856
The relation between axonal conduction velocity (CV), and the tetanic tension (TT) and twitch contraction time (CT) of motor units was explored in 3 cat hind limb muscles, planaris, flexor hallucis longus and flexor digitorum brevis. The motor units were functionally isolated by separation of ventral root filaments containing single .alpha. axons to the muscle whose tendon of insertion was connected to a strain ring. Motor unit sample sizes were more substantial, both within and between experiments than were available in the literature, with: 114 units from 5 plantaris experiments; 124 units from 3 flexor hallucis longus experiments; and 60 units from 4 flexor digitorum brevis experiments. Despite this substantial sampling and contrary to prevailing opinion, no significant relation was encountered between CV and TT and CT. Motor units of some small muscles, such as the lumbricals, may show a far closer relation between CV, TT and CT than the motor units of larger muscles such as the major force contributors to the ankle and toe joints. Relations between motoneuron size, axon size and muscle contractile parameters are less precisely related than usually assumed in the literature.