Somatotopic relations between spinal motoneurones and muscle fibres of the cat's musculus peroneus longus.

The cat's m.peroneus longus was analyzed with respect to the somatotopic relation between the rostro-caudal site of emergence of ventral root filaments (i.e. rostro-caudal site of motoneurones) and the intramuscular distribution of innervation. Rostro-caudally distinct fractions of ventral roots were stimulated repetitively in order to deplete their respective muscle fibres of glycogen. The intramuscular position of glycogen-depleted fibres was analyzed in transverse sections from different proximo-distal levels. At each level, depleted muscle fibres were dispersed across the whole muscle. No consistent relation was found between the spinal site of origin of a ventral root filament and the proximo-distal distribution of its fibres within the pennate muscle. A significant and evident tendency was found, however, for rostral root filaments (i.e. rostral motoneurones) to innervate a greater number of muscle fibres in anterior than in posterior muscle portions. For caudal root filaments, the opposite pattern of innervation was observed.