THE ORGANIZATION OF ACROMIODELTOID AND SPINODELTOID MOTOR NUCLEI IN RAT SPINAL-CORD

The retrograde intraaxonal transport of fluorescent dyes (10% Bisbenzi mide or 2% Nuclear Yellow) was used to identify the motoneuron populat ions that control two prime movers of the rat shoulder joint, the acro miodeltoid (Ad) and spinodeltoid (Sd) muscles. The Ad and Sd motor nuc lei were both comprised of an average of 30-40 motoneurons distributed between spinal segments C5 and C7, in lateral regions of Rexed's lami na IX. Although there was considerable overlap among them, the center of the Ad motor nucleus was consistently located more rostral and medi al than that for the Sd motor nucleus.