NEURO-MUSCULAR MECHANISM 



107 



B. PROPRIO-CEPTIVE SPINAL MECHANISM 

 Kinaesthetie OP Muscle and Joint Sense 



The importance of the action of the receptors which are 

 stimulated by the action of muscles has been indicated in the 

 study of retiex action (p. 96). A double mechanism is in- 

 volved 1st, A mechanism stimulated by the contraction of 

 the muscles ; and 2nd, a mechanism acted 

 on by movements at the joints. The re- 

 ceptors are of three kinds : 



(1st) Muscle Spindles. Among the fibres 

 of the muscles are found long fusiform 

 structures containing modified parts of the 

 muscle fibres. Into each spindle a medul- 

 lated nerve passes and breaks up into a 

 non-medullated plexus round the fibres 

 (fig. 48). 



(2nd) Organs of Golgi are small fibrous 

 capsules in the tendons near the muscle 

 fibres into which a medullated fibre enters, 

 and losing its white sheath forms a plexus 

 of fibrils with varicosities upon them. 



(3rd) Varicose terminations of axons sur- 

 rounded by fibrous tissues are found in the 

 synovial membranes and round joints. 



Through these mechanisms information 

 is transmitted to the central nervous system 

 as to the position and movements of the various parts, and 

 this, as has been already indicated, although not necessarily 

 modifying the consciousness, is of the utmost importance in 

 guiding the movements. When the consciousness is affected, 

 valuable information as to the conditions of the surroundings 

 may be gained. In estimating the weight of bodies, these 

 sensations are much used. The body to be weighed is taken 

 in the hand, and by determining the amount of muscular con- 

 traction required to support or raise it, the weight is estimated. 

 The shape and size of objects are also determined by this sense 

 in conjunction with the sense of touch by estimating the 

 distance through which the limb touching it may be moved in 



FIG. 48. Structure 

 of muscle spindle 

 only one fibre repre- 

 sented. 6, capsular 

 space ; c, capsule ; 

 p, motor termina- 

 tion ; T.S., sensory 

 termination on the 

 spindle fibre. (From 

 RKGAUDand FAVRE.) 



