Neural pathway involved in the excitation of motoneurones to jaw-opening muscles by stimulation of the orbital cerebral cortex in the cat.

The pathway and synaptic basis for the efferent discharge in the digastric nerve evoked by stimulation of the orbital cortex were studied in cats anesthetized with alpha-chloralose. Transection of the brain stem at the boundary between the pons and the medulla oblongata abolished discharge. Intracellular recording from anterior digastric motoneurones revealed that the orbital cortical stimulation evoked excitatory post-synaptic potentials with a latency that was longer by one synaptic delay than that of spike potentials evoked in medial bulbar reticular neurones making a direct excitatory projection to anterior digastric motoneurones. It was concluded that the excitatory effects was mediated by the medial bulbar reticular formation.