Brainstem facial-motor pathways from two distinct groups of stapedius motoneurons in the cat
Article first published online: 9 OCT 2004
Copyright © 1989 Alan R. Liss, Inc.
Journal of Comparative Neurology
Volume 287, Issue 1, pages 134–144, 1 September 1989
How to Cite
Guinan, J. J., Joseph, M. P. and Norris, B. E. (1989), Brainstem facial-motor pathways from two distinct groups of stapedius motoneurons in the cat. J. Comp. Neurol., 287: 134–144. doi: 10.1002/cne.902870110
- Issue published online: 9 OCT 2004
- Article first published online: 9 OCT 2004
- Manuscript Accepted: 12 APR 1989
- acoustic reflex;
- facial nerve;
- cranial nerves;
- motor control
To determine the brainstem origins and axonal routes of stapedius motoneurons, we labeled motoneurons by injecting cat stapedius muscles with horseradish peroxidase. Some injections were made in normal cats and some in cats in which the middle segment of the internal facial genu had been cut. By tracing labeled axons and by comparing the locations of labeled cell bodies in normal and lesioned cats, we divided stapedius motoneurons into two groups: “perifacial” and “accessory.” Perifacial stapedius motoneurons have cell bodies located around the motor nucleus of the facial nerve and axons which follow the classical course of facial motor axons through the internal genu of the facial nerve. Accessory stapedius motoneurons have cell bodies near the descending facial motor root and axons which ascend to the rostral tip of the internal facial genu, abruptly reverse direction, and then join the descending facial motor root. The sharply hooked course of axons of accessory stapedius motoneurons is similar to the course of axons from other accessory nuclei of cranial nerves V-VII. Our present results, with those of McCue and Guinan (J. Neurophysiol. 60:1160–1180, '88), demonstrate that cats have two groups of stapedius motoneurons which can be separated anatomically by the locations of their cell bodies or by the courses of their axons, and which, on the average, have different response properties.