[Role of different types of infraorbital nerve fibers in synaptic activation of masticatory muscle motoneurons].

The PSPs of the masseter and digastric motoneurons evoked by stimulation of the infraorbital nerve by stimuli from 1 to 10 thresholds were studied in cats anesthetized with chloraloze and nembutal. Masseter motoneurons were divided into two groups. The first group masseter motoneurons responded to 1-2.5 threshold infraorbital nerve stimulation by short latent EPSPs. An increase in the impulse strength to 3-9 thresholds led to appearance of IPSPs with 2.8-3.5 ms latency in these motoneurons. The second group masseter motoneurons responded to 3.9 threshold stimulation of the infraorbital nerve by IPSPs with 6.8 ms latency. The strength of stimuli below 3 thresholds evoked no PSPs in these neurons. Stimuli of 1.1-2.0 thresholds evoked EPSPs in digastric motoneurons but an increased stimulation led to generation of action potentials. It is supposed that existence of different inputs is a basis for functional diversity of jaw-closing and jaw-opening reflexes.