The innervation of muscle spindles in the snake, Elaphe quadrivirgata

The morphology and distribution of sensory endings in snake (Elaphe quadrivirgata) muscle spindles was studied in silver preparations. The sensory axon supplying long-capsule spindles often bifurcates before or after penetrating the capsule and runs for some distance along the intrafusal fibre. The sensory axon supplying short-capsule spindles penetrates the capsule at a sharp angle, and, without ramification, terminates abruptly on the intrafusal fibre. The sensory terminal is composed of terminal bulbs and small links. In long-capsule spindles the sensory ending is arranged longitudinally in one or two rows. The sensory ending in short-capsule spindles ramifies extensively, covering densely the intrafusal fibre. The area occupied by sensory bulbs was estimated to be slightly higher in short-capsule (15-17?) THAN IN LONG-CAPSULE SPINDLES (12-13). The functional significance of these findings is discussed. Motor innervation of muscle spindles in the snake Elaphe quadrivirgata was studied using AchE staining for light microscopy in conjection with electron microscopy. In the polar region of either type of spindle, the majority of the motor endings are of grape type. In long-capsule spindles plate endings may occur in the spindle pole as well as in the capsular region. Motor endings in the capsular region are mostly of plate type. Plate endings rarely occur in short-capsule spindles. Identified single motor endings were studied by electron microscopy. Intrafusal grape endings are characterized by a smooth post-synaptic membrane. Intrafusal plate endings in the polar region are characterized by junctional folds or gutterings; plate endings in the capsular region show less developed gutterings or indentations. The distribution of intrafusal motor endings was examined along the length of single intrafusal fibres. The long-capsule spindle often receives asymmetrical motor innervation around the capsular region, whereas motor endings in the short-capsule spindle distribute more symmetrically.