Two distinct descending inputs to the cricothyroid motoneuron in the medulla originating from the amygdala and the lateral hypothalamic area.
1. The retrograde labelling study revealed that there are at least two independent descending pathways from the limbic system to the ventral medulla, i.e., the hypothalamo-medullary pathway and the amygdalo-medullary pathway. 2. The stimulation in the lateral hypothalamic area produced parasympathetic excitation and vocalization response: the recruited motor unit of CT muscle occurred in the late expiratory phase. By contrast, the stimulation at the medial part of the amygdala evoked sympathetic excitation and expiratory braking: the recruited motor unit of CT muscle occurred in the early expiratory phase or in the post-in-spiratory phase. 3. The present physiological study provided further important information on dual innervation of the cricothyroid muscle of the larynx: one motor unit with inspiratory firing is generated in the medulla, whereas the other motor unit with expiratory firing is evoked by a descending input from the limbic system.