1. Central Location of Motoneurons Supplying the Muscles Which Partake of Swallowing and Phonation

Abstract

Central location of motoneurons for each muscle which partakes of swallowing and phonation was investigated in cats utilizing the horseradish peroxidase (HRP) method. HRP labeled neurons were identified in the nuclei of the brain-stem and Cl, C2 ipsilaterally except for the esophageal muscle. The motoneurons supplying the various muscles which participate in important functions during swallowing and phonation were recognized in the nucleus ambiguus.
The somatotopical organization of the motoneurons in the nucleus ambiguus was determined using the same method and was confirmed by electrical stimulation of the nuclei of some selected muscles.
The direct corticobulbar connection to the nucleus ambiguus was studied by means of the anterograde and retrograde axonal transport technique using WGA-HRP. We were not able to determine any nerve fibers which run from the motor cortex to the nucleus ambiguus.