Anatomy of medial gastrocnemius and soleus motor nuclei in cat spinal cord

Publisher Website
Google Scholar
Abstract
The number, size and position of motoneurons labeled with horseradish peroxidase (HRP: Sigma, Type VI) after intramuscular injection into either the medial gastrocnemius (MG) or soleus (SOL) muscles were studied in adult cats. Labeled motoneurons were found in a discrete longitudinal column in segments L7 and S1, with the main concentration of SOL cells somewhat rostral to that of MG. Within the caudal half of the region of MG and SOL nuclear overlap, more than 96% of all neurons present in the target cell column were labeled. The average soma diameters of MG and SOL motoneurons were bimodally distributed; about 25-30% of the cells were small (average soma diameter 18-38.5 .mu.m) and were regarded as .gamma.-motoneurons, the other 70-75% were larger (38.5-78 .mu.m diameter) and were regarded as .alpha.-motoneurons. The size distribution of .gamma.-cells was similar in the MG and SOL nuclei but the MG nucleus contained many more large .alpha.-motoneurons (diameter greater than 50 .mu.m) than the SOL. Labeled .gamma.- and .alpha.-motoneurons were intermingled throughout the entire length of both MG and SOL cell columns. The rostral third of the MG cell column contained a higher than expected percentage of the largest .alpha. motoneurons. The latter finding was correlated with a non-uniform distribution of muscle fiber types (and therefore of motor unit types) within the MG muscle.