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CHORDATE ANATOMY 



MUSCLE SPINDLES 



Muscle spindles form a special set of sensory nerve terminations 

 upon muscle fibers, by means of which we are able to sense the degree of 

 contraction of a muscle and the position of parts of the body. Such 

 neuro-muscular spindles are found in vertebrates, beginning with the 

 Amphibia. As their name suggests, they are spindle-shaped structures 

 located among the fibers of a muscle, usually near where the muscle joins 

 a tendon. 



MUSCLE FIBERS DENDRITES 



RINGS SPIRALS SHEATH 



SHEATH 



Fig. 373. — A portion of a muscle spindle from a gold-chloride preparation of a cat 

 muscle. The sensory nerve terminations take the form of spirals, or rings, or branched 

 dendrites. A connective-tissue sheath surrounds the spindle. CRedrawn from Jordan 

 and Ferguson, after Ruffini.) 



Each spindle usually consists of several striped muscle fibers attached 

 to a tendon at one end and to intramuscular connective tissue at the other. 

 One or more nerve fibers connect with the spindle. Each nerve fiber 

 terminates within the spindle in the form of a spiral encircling a muscle 

 fiber. 



Neuro-tendinous spindles resemble muscular, but are connected with 

 tendons. These also serve to indicate the amount of muscular work and 

 the resistance overcome. 



