122 ANATOMY AND PHYSIOLOGY 



and relaxation of the diaphragm, the whole body of abdominal and 

 pelvic organs moves upward, and vice versa. 



Passing to the consideration of more complicated movements. 

 For respiration we must have the muscles of the thorax; for 

 swallowing or deglution, the muscles of the tongue and throat; for 

 speaking, those of the tongue and face. 



The arms and hands become organs of prehension when by use 

 of their numerous muscles they reach out to gather things in; the 

 lower limbs are organs of locomotion, only because their muscles 

 enable them to bear and transport the body from place to place. 

 Even the ability to stand still is due to a balanced tension of mus- 

 cles, which keeps the joints quiet. 



Finally, various emotions may be expressed by muscle-action 

 without a spoken word, both by changes of the face (referred to, 

 .p. 88) and gestures of the body. Compare the erect posture of 

 the person ready and alert, with the drooping figure of despond- 

 ency or the lax one of indolence. Read the meaning of the firm, 

 quick footstep, and contrast it with the uncertain and halting 

 one. Note how the hand may welcome, or repel. Even the eye 

 would be far less expressive were the iris immovable. Indeed, 

 we might well see a literal meaning in the old adage " Actions 

 speak louder than words." Thus muscle action means much 

 more than simple movement, and it all depends ultimately upon 

 the specially developed attributes of the muscle cell contractility, 

 extensibility, elasticity. 



And thus we find that all functions of the body depend in the 

 beginning upon muscle action, as the heart itself is a collection of 

 muscles influencing the entire body, since without circulation of 

 blood all processes of life must cease. 



Muscle Stimulus. The action of skeletal muscles as we 

 ordinarily see them, expresses the result of the response of muscle 

 tissue to the natural and direct stimulus of nerves. (Nerve im- 

 pulses 1 originate in the brain and spinal cord in response to sense 

 impressions, and will be studied in connection with the nervous 

 system.) Certain other stimuli cause temporary muscle action 

 for example, the contact of acids (chemical], a sharp blow (mechan- 

 ical), electricity, etc. 



Allusion has already been made to the tension of muscles pro- 



1 An unsatisfactory term, but in common use. 



