Distribution of motoneurones to the neck muscles, biventer cervicis, splenius and complexus in the cat

TLDR

The study mapped motoneurones innervating the cat dorsal neck muscles biventer cervicis, splenius, and complexus using retrograde horseradish peroxidase transport. Researchers compared HRP uptake from direct muscle injection versus cut nerve exposure, ultimately using cut nerve exposure to delineate individual motoneurone pools. Labeling revealed 10–70 µm motoneurones, mostly under 40 µm, concentrated in the ventromedial nucleus and medial ventral horn border, with substantial overlap among the three muscles, plus splenius cells in the spinal accessory nucleus and motoneurones in commissural, centrodorsal, and ventral commissure regions.

Abstract

Abstract The distribution of motoneurones to the cat dorsal neck muscles biventer cervicis, splenius and complexus has been examined using the technique of retrograde horseradish peroxidase transport. A comparison was initially made of HRP uptake into motoneurones produced either by injecting HRP solution directly into a singly neck muscle or by exposing the cut ends of motor nerves to an HRP solution. The injection of HRP into single neck muscles was found to produce widespread labelling of motoneurones presumably due to diffusion of HRP into adjacent muscles. For the examination of individual motoneurone pools the technique of cut nerve exposure was therefore used. Labelled neck muscle motoneurones ranged from 10–70 μ in diameter, but the majority of cells had diameters which were less than 40 μ. Most cells were located in the ventromedial nucleus and along the medial border of the ventral horn. In these regions there was considerable overlap between the motoneurones pools of the three neck muscles examined. In addition, some splenius motoneurones were located in the nucleus of the spinal accessory nerve. Labelled neck muscle motoneurones were also located in areas not usually considered to contain motoneurones such as the commissural and centrodorsal nuclei and in the ventral commissure.