MOTION 



51 



forms a meniscus. If the muscle is now made to contract, it will be 

 seen that the meniscus does not move. 



The Excitation of Muscle. — We have seen that all movements 

 which are to be carried out with precision, are effected by means of 

 striated muscle. In nearly all cases this tissue is under the control 

 of the central nervous system and especially of the cerebrum which 

 gives rise to volition. Non-striated muscle, on the other hand, is not 

 absolutely dependent upon central nervous structures, but is regulated 

 by peripheral or local centers. For this reason, it is able to show a 

 marked degree of spontaneity and is, therefore, not wholly under the 

 guidance of the will. It is true, however, that its independency is 

 not absolute, because its connection with the 

 cerebrospinal system is necessary to bring it into 

 functional relation with other parts of the body. 



The different muscles are connected with the 

 central nervous system by means of nerves which 

 conduct impulses either toward them or away 

 from them. Hence, muscle tissue must be in 

 possession of two types of end-organs, namely 

 one for the reception of the stimuli and one for 

 the production of the motor reaction. The sen- 

 sory end-organ or muscle-spindle , is composed of 

 a group of delicate fibers which are invested by 

 a thick covering of perimysium. Around these 

 the nerve terminals are arranged in the form of 

 spirals or rings. The motor end-organ, or motor 

 plate, consists of a bulbular enlargement of the 

 axis cylinder which is pressed flat against the Show That Contract- 



T . ^ ,1 1 r«i T, ING Muscle Does Not 



sarcolemm^ of the muscle fiber. It 



Fig. 23.— Schema to 



appears as change Its Volume. 



a rounded granular mass, the substance of which 

 contains numerous nuclei. 



M, meniscus of sa- 

 lt is invested solely ^^^^ solution; ,S, elec- 

 trodes ^'^ '^ — 1----1- 



1 1 r* i_ • J* J.1 J.' 'J.^ troues through which 



by neurolemma which is directly continuous with ^^^^^^ j^ receptacle is 

 the sarcolemma. The medullary sheath dis- stimulated, 

 appears at some distance from the motor plate, 

 namely, at the point where the nerve fiber begins to divide to form this 

 ramification of axis cylinders. Most generally, a single muscle fiber 

 contains only one of these motor plates, but if it is very long, it usually 

 embraces two or several of these endings. The different nerve fibrils 

 arising from these plates, unite into larger ones so that their number 

 is much reduced when leaving the muscle. That this is a very econom- 

 ical arrangement may be gathered from the fact that inasmuch as a 

 muscle, such as the oculomotorius, contains about 15,000 muscle fibers, 

 about 180 million nerve fibers would be required for 30,000 grams of 

 muscle substance. Stilling, however, has found only about 30,000 

 fibers in the anterior roots of the spinal cord. In smooth muscle, the 

 individual nerve fibers terminate in complicated networks which are 



