Monosynaptic excitation of motoneurons of individual forelimb muscles.

Abstract

Intracellular records were made from motoneurons of individual muscle nerves of the fore-limb in anesthetized cats. Monosynaptic excitatory transmission could be enhanced by posttetanic potentiation in the cervical spinal cord, much as it can in the lumbosacral cord. Posttetanic potentiation was employed to help ascertain the presence or absence of small excitatory postsynaptic potentials (EPSPs). EPSPs with latencies less than 1.25 msec. were considered monosynaptic. Some of the monosynaptic excitatory connections found were appropriate in terms of the myotatic unit hypothesis. However, some were not. In particular, there were often monosynaptic excitatory interconnections between the extensor digitorum communis and lateralis nerves and the flexor digitorum profundus branches. It is suggested that these unexpected connections may be related either to cocontraction of these muscles or to complicated movements of the wrist or possibly claws.