Heterotopic nociceptive EMG-reactions in M. masseter.

Peculiarities of EMG-reactions of m. masseter to noxious homo- and heterotopic stimulation were studied on healthy volunteers. Homotopic noxious electrical stimulation of n. mentalis elicited several successive responses in m. masseter consisting of R-component, early exteroceptive suppression period, early excitation period, late exteroceptive suppression period, and late excitation period. Heterotopic noxious stimulation (forehead, ear lobe, index finger) induced only the late exteroceptive suppression period and late excitation period. It is concluded that the excitatory components have a reflex nature, and that the late exteroceptive suppression period is formed under the effect of central cerebral structures, which mediate their influence via the spinal-corticospinal return loop.