Localization of the motor neurons to the tensor tympani muscle

The localization of the motor neurons to the tensor tympani (TT) muscle was studied using the method of retrograde transport of horseradish peroxidase (HRP). After intramuscular injections of HRP, specifically labeled neurons were found in the ventral, parvocellular portion of the trigeminal motor nucleus. These cells had a medial relation to the rootlets of the trigeminal nerve and, rostrally, to the lateral lemniscus. The results are compared to those of other investigators and a generalization is suggested for the localization of these neurons which allows for species variation. Other incidental findings are also discussed.