Brain-stem representation of jaw muscle activities of the dog.

Abstract

1. The electromyographic discharges of rigid jaw mucles in the decerebrate cat were dominant in the suprahyoid muscle groups and scanty in the jaw closing muscle groups. But the jaw closing muscles were sensitive to stretching and showed strong spastic resistance to even a slight opening of the mouth.2. In spite of the marked extensor rigidity of the limbs, jaw rigidity disappeared readily after decerebration at a level caudal to the mesencephalic trigeminal nucleus.3. Regular spontaneous unit discharges were recorded from and along the mesencephalic trigeminal nucleus and root of the dog. The background activity in these points was remarkably depressed by elevating the lower jaw and accelerated by depressing the jaw. These responses were obtained by strictly localized punctures in the brain-stem, accompanied by a short latency and slow adaptation as shown in goat by Cooper, Daniel and Whitteridge.4. Nearly the same response was recorded in the lateral bulbar reticular formation at points just caudal to the cerebellar peduncles. There were also some localized points in the medial bulbar reticular formation near the hypoglossal nucleus at level rostral to the inferior olive, in which the background activity was inhibited by opening of the mouth.