Discharge rate and reflex responses of fusimotor neurons during muscle ischemia.

Reflex effects of muscle ischemia on fusimotor neurons were investigated in decerebrate cats. Nerve impulses of single fusimotor neurons were recorded from filaments cut out of otherwise intact nerves to triceps surae muscles. Muscle ischemia was induced by clamping a. and v. femoralis. Fusimotor discharge rate was counted before, during, and after ischemia of both resting and contracting muscles. Muscle contractions were induced either by direct electrical stimulation or reflexly by muscle stretch. No changes were found in either the mean discharge rate or in the reflex response of fusimotor neurons to muscle stretches and contractions during muscle ischemia. It could be concluded that group III and IV muscle afferent fibers, responding to contractions of the ischemic muscle, have no reflex effects on fusimotor neurons. It also does not seem probable that fusimotor neurons contribute to ischemic muscular cramps.