Topographic arrangement of motoneurons innervating the suprahyoid and infrahyoid muscles. A horseradish peroxidase study in cats.

The topographic arrangement of motoneurons innervating the muscles which participate in the rostrocaudal movement of the larynx was studied in cats by means of the horseradish peroxidase (HRP) method. After HRP injection into these muscles, all labeled neurons were found in the nuclei of the brainstem and cervical nerves (C1, C2) ipsilaterally. The mylohyoid and anterior digastric motoneurons were seen in a cluster in the medial part of the rostrocaudal area of the motor trigeminal nucleus. Within the medial part of the nucleus, the mylohyoid motoneurons were located ventrally and the anterior digastric motoneurons dorsally. The posterior digastric neurons were situated in the accessory facial nucleus, the stylohyoid neurons in the ventral aspect of the facial nucleus, the geniohyoid motoneurons in the ventral aspect of the hypoglossal nucleus, and the thyrohyoid motoneurons in the lateral aspect of the hypoglossal nucleus and the dorsomedial part of the ventral horn cells of C1. The HRP-labeled neurons of the sternohyoid and sternothyroid muscles were observed in the central portion of the ventral horn cells of C1 and C2.