NERVE 



105 



the muscles, tendons, and joints which are stimulated by 

 movements generally originated by stimuli from without, and 

 which we have already seen (p. 88), may have an important 

 influence on the course of the movements produced. These 

 are one kind of the group of receptors which Sherrington has 

 called Proprioceptors. They might be called the muscle- 

 joint receptors. 



III. Muscle and Joint (Proprioceptive). 



A double mechanism is involved — 1st, A mechanism 

 stimulated by the contraction of the muscles ; and 2nd, a 

 mechanism acted on by movements at the joints. 



A. Structure — (1st) Muscle Spindles. — Among the fibres 

 of the muscles are found long fusiform structures containing 

 modified muscle fibres. Into each spindle 

 a medullated nerve passes and breaks 

 up into a non-medullated plexus round 

 tliese fibres (fig. 45). That these nerves rs 

 are ingoing and not ordinary motor fibres , 

 is shown by the fact that they do not .^ 

 degenerate when the anterior root of a 

 spinal nerve which carries the motor 

 fibres is cut, but that they do degenerate 

 when the posterior root is cut outside the 



ganglion. 



Fig. 45. — Structure 

 of muscle spindle 

 — only one fibre re- 

 presented, b, cap- 

 sular space ; c, cap- 

 sule ; p, motor 

 termination; T.S., 

 sensory termina- 

 tion on the spindle 

 fibre. {From Re- 

 gaud and Fayre.) 



(2nd) Organs of Golgi are small 

 fibrous capsules in the tendons near the 

 muscle fibres, and into each a medul- 

 lated fibre enters, and, losing its white 

 sheath, forms a plexus of fibrils with 

 varicosities upon them. 



(3rd) Varicose terminations of axons 

 surrounded by fibrous tissues are found 

 in the synovial membranes and round joints. 



B. Physiology. — Through these mechanisms information 

 is transmitted to the central nervous system as to the position 

 and movements of the various parts, and this is of the 

 utmost importance in modifying and guiding the movements 

 without consciousness being necessarily implicated (p. 83). 



