The mandibular common inhibitor system

Summary The mandibular common inhibitor neurones ofHomarus gammarus receive sensory input from a wide receptive field (Table 1, Figs. 2, 3) and from their symmetrical homologue (Ferrero and Wales, 1976).The CI system receives excitatory input from mandibular proprioceptors, with the notable exception of the mandibular muscle receptor organ, and its activity increases, during mandible opening and closing, towards the extremes of movement (Fig. 1). The output of CI neurones is usually coupled except during some high frequency bursts. Unilateral sensory input usually produces a coupled output. Electrical stimulation of a wide range of mandibular nerves (Table 2) has a similar effect and entrains the CI output at lower frequencies (Figs. 4, 5).Antidromic stimulation of a CI neurone causes excitation of its homologue but to a lower level of activity and without enhanced coupling. Even when the excitatory state is raised, by concurrent stimulation of a sensory nerve, the pathway activated by antidromic stimuli does not produce coupled activity at frequencies above 20 Hz (Fig. 8).Stimulation with single pulses will frequently produce short trains of impulses from the CI neurones (Figs. 6, 7) suggesting reciprocal excitation between the neurones.A model of the system based on current knowledge is presented.