Human jaw muscle motor behaviour. II. Reflex and receptor mechanisms.

The stretch reflex is much more complicated than the simple tendon jerk with a monosynaptic reflex pathway. Muscle stretch is not a necessary prerequisite to elicit the short latency EMG excitatory response. Long latency EMG responses are probably of greater functional importance. The silent period (SP) following the jaw jerk is prolonged in patients with symptoms of mandibular dysfunction. In the individual case, however, measurement of the SP may not be of diagnostic value. The Golgi tendon organs are highly sensitive tension receptors which play a much larger role in the proprioceptive regulation of muscle tension than has been believed in the past. So-called type P mechanoreceptors which like a large part of the periodontal receptors have their cells of origin in the mesencephalic nucleus V, have been found in the hard palate. The majority of periodontal mechanoreceptors are slowly adapting and thus able to respond with sustained discharge to long lasting stimulation, as during chenching or bruxing. The postural position has been assigned great clinical significance. It has been assumed that this position is constant throughout life. It has, however, been observed that the postural position rapidly adapts to changes of the vertical occlusal dimension.