MUSCLE READING 



4011 



MUSCLES 



MUSCLE READING. See MIND READING. 



MUSCLES, mus"lz. When a person walks 

 from one place to another, picks up his food, 

 puts on his clothing or performs any other of 

 the countless movements that are a part of 

 everyday life he calls to service certain im- 

 portant bodily organs known as muscles. 

 There are over 500 of these in the human body, 

 and they constitute fully half its weight. They 

 are the lean flesh of man ; the muscles of a cow 

 form the lean meat of beef, and those of a pig 

 lean meat of pork. There are two great 

 classes of muscles, voluntary and involuntary. 

 rmediate between these is heart muscle, 

 which, though it acts like an involuntary mus- 

 cle, is similar to a voluntary muscle in struc- 

 ture. 



Voluntary Muscles. These are the muscles 

 which move according to the will of a person 

 and are under his direct control, as the ones 

 used in walking, swimming or playing ball. 

 -c muscles are for the most part placed 

 next to the bones, and they serve not only as 

 movement organs, but also to round out the 

 figure and so impart beauty to the body. In 

 its typical form such a muscle consists .of a 

 soft red middle portion which tapers towards 

 each end; it is attached to some part of the 

 bony framework by white, inelastic cords called 

 tendons (which see). When the middle portion 

 is stimulated through its nerves it contracts, 

 and in so doing it exerts a pull on the tendons, 

 pull is then transmitted to the part to be 

 moved. A muscle which has two divisions at 

 one end is called a biceps muscle (two-headed), 



(a) Bleeps 

 (6) Triceps 



--a 



BICEPS AND TRICEPS MUSCLES 



that in the front of the arm between the 

 and elbow. When the elbow is bent 

 muscle swells and becomes thicker and 

 harder; a biceps "hard as a rock" is the boast 

 MV a schoolboy who leads an active life. 

 > ps (three-headed) muscle, like that at 

 the back of the upper arm, has three divisions. 



According to structure a voluntary muscle is 

 made up of bundles of fibers about an inch 

 long and about ^oo of an inch wide, each the 

 development of a single cell. Under the micro- 

 scope these fibers are seen to be marked cross- 

 wise with fine alternating bands of dark ancl 

 light. From this comes the name striated 

 (striped) muscle, which is another term for 

 voluntary muscle. The bundles of fibers are 

 enclosed in an elastic sheet of thin membrane 

 called the sarcolemma, a word meaning rind 

 or skin; they are supported and protected by 

 connective tissue, penetrated by nerves from 

 the cerebrospinal system and supplied with 

 blood vessels. Some voluntary muscles, such 

 as those which are concerned in the process of 

 breathing, are both voluntary and involuntary 

 in respect to function. That is, breathing may 

 be controlled by the will, but ordinarily it goes 

 on mechanically, and during slumber its action 

 takes place without the least exercise of the 

 will. 



Involuntary Muscles. The involuntary mus- 

 cles are those whose contractions are beyond a 

 person's control, and which lie in the walls of 

 such organs of the body as the stomach, intes- 

 tines and arteries. No effort of the will can 

 move such muscles. The muscles which by 

 their contraction and relaxation move the food 

 about in the stomach belong to this class. 

 Structurally they are said to be unstriated, or 

 not striped, for they lack the crossbands char- 

 acteristic of striped muscles. Involuntary mus- 

 cles are made up of elongated, spindle-shaped 

 cells, each of which tapers towards its ends and 

 has a central nucleus. These cells vary in 

 length from %oo to Moo of an inch, and are 

 from %ooo to Mooo of an inch wide. Involun- 

 tary muscles are penetrated by nerves from tin- 

 sympathetic system (see NERVOUS SYSTEM). 



Muscular Development. Weak, flabby mus- 

 cles are an indication of physical inactivity, for 

 muscles grow larger and stronger through use. 

 Systematic development of these organs stimu- 

 lates the fundamental processes through which 

 hfr is sustained digestion, Hrnilation and 

 breathing and the whole body will therefore 

 grow more vigorous if the muscles are properly 

 exercised. For tins reason, walking, rou 

 swimming and other forma of exercise and 

 recreation should be practiced by everyone, 

 especially by those whose work keeps them in- 

 active several hours each day. Boys and girls 

 who have allowed themselves to grow stoop- 

 shouldered can strengthen the weak and in- 

 active muscles of the back by proper exercise; 



