A study of single and complex types of Muscle Spindle in Extensor Digitoriiim communis muscle of rabbit, Rat and Mouse

The present study has been designed to provide the literature with some characteristic features of muscle spindles in the forelimb Extensor digitorum communis (e.d.c) muscle of rabbit, rat and mouse through examination of their number, distribution and morphology. This muscle was chosen because it is expected to be rich with spindles due to its role in controlling the extension of the digits 2,3,4 and 5 also because very little is known about the receptors in this muscle. The study has been carried out by two histological techniques hematoxylin-eosin stained technique and silver nitrate preparations. Spindles were generally seen distributed throughout the entire length of the muscles, although a few spindles were seen concentrated in a certain region of cross section where blood vessels and nerve entry region located. Spindles in rabbit, rat and mouse muscles were generally similar in their basic structures when compared with those of other mammals. Also this study revealed the presence of two unique spindles in one of the rabbit muscles, the first was containing four bags and the second was containing alarge fiber inside the peraxial space. Complex spindles were common in all muscles, although there were individual differences of each kind in each muscle. The present study confirmed the presence of intrafusal capillaries in rabbit muscles. Spindles in rabbit and rat muscles were innervated by both primary and secondary ending, also presence of spindles in rabbit and rat with double primary and devoid of secondary ending