8o TEXT-BOOK OF PHYSIOLOGY. 



The term phasic is applied to these currents. The first current flows in the 

 muscle in the direction of progress of the contraction wave first phase; the 

 second current flows in the reverse direction second phase; the current is 

 therefore diphasic. When a muscle is tetanized, there is but a single current 

 observed, which, however, endures so long as the tetanic contraction is 

 maintained. To this current the term decremential is given. When a 

 muscle is excited to action by the nerve impulse which enters at its center, 

 two contraction waves are developed, one in each half of the muscle, and 

 hence there are two sets of diphasic action currents. 



The presence of action currents in the muscle of the living body during a 

 single contraction was demonstrated by Hermann in the muscles of the 

 forearm. The arrangement of the experiment was, briefly, as follows: 

 The forearm was surrounded by two twine electrodes saturated with zinc 

 solution, one being placed at the physiologic middle the nervous equator 

 the other at the wrist. Both electrodes were then connected with the galvan- 

 ometer. When the brachial plexus was stimulated in the axillary space, the 

 deflections of the galvanometer needle, when analyzed with the repeating 

 rheotome, indicated phasic currents with a single contraction. In the first 

 phase atterminal the wrist became positive and the current passed in the 

 muscle toward its termination; and in the second abterminal it became 

 negative and the current now passed in the reverse direction. The action 

 currents which are observed in the frog's muscle were thus shown to be 

 present in the living human muscle, with this difference, however: that the 

 second phase abterminal instead of being weaker in man, is equally 

 strong with the atterminal. This experiment also revealed the fact that the 

 rapidity of propagation of the excitation wave was much greater in man, 

 amounting to about twelve meters per second. Hermann therefore denies 

 the pre-existence of electric currents and regards them as due to localized 

 temporary disintegration of the muscle in consequence of activity, as they 

 disappear on the restoration of the muscle to its normal condition. 



SPECIAL ACTION OF MUSCLE GROUPS. 



The individual muscles of the axial and appendicular portions of the 

 body are named with reference to their shape, action, structure, etc.; e.g., 

 deltoid, flexor, penniform, etc. In different localities a group of muscles 

 having a common function is named in accordance with the kind of motion 

 it produces or to which it gives rise: e.g., groups of muscles which alternately 

 diminish or increase the angular distance between two bones are known 

 respectively as flexors and extensors; such muscle groups are usually found 

 in association with ginglymus joints. Muscles which rotate the bone to 

 which they are attached around its own axis without producing any great 

 change of position are known as rotators, and are found in association with 

 enarthrodial or ball-and-socket joints. Muscles which impart an angular 

 movement to the extremities to and from the median line of the body are 

 termed adductors and abductors respectively. 



In addition to the actions of individual groups of muscles in producing 

 special movements, in some regions of the body, several groups of muscles 

 are coordinated for the accomplishment of certain definite functions; e.g., 



