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II \MHli K IK i II- PHYSIOLOGY 



NEUROPHYSIOLOGY III 



further means of action. "The wealth of sensibility, 

 the control of binocular vision, the progress of in- 

 telligence and of creative imagination, the tenacity 



of purpose, all converge towards the realization of 

 this admirable tool to which, from the time ol Hippoc- 

 rates, Aristotle and Galen up to the present day, 

 philosophers, doctors, physiologists and psychologists 

 and also the most meditating laymen have directed 

 (heir thoughts ...'"( i 18). 



These preliminary considerations, inspired by the 

 data of phylogenesis and ontogenesis, help us to 

 realize the unique place held by skilled movements 

 among the forms of expression of motor capacity 

 and the ties that bind their neurophysiological stuck 

 to that of the higher functions of the nervous system. 



FIG. 2. Models of joints. Left: A hinge joint, with a single 

 degree of freedom, moved by a pair of antagonistic muscles. 

 Right : A ball joint, with free rotational motion, operated by 

 four muscles. [From Weiss (130).] 



PERtPIIEKAl EXPRESSION OF SKILLED MOVEMENTS 



We shall try, as a first step, to describe the condi- 

 tions and the forms of expression of skilled move- 

 ments at the level of the peripheral organs. 



Conditions of Ex/ni ssion 



Movement is the result of the motor activity of 

 the muscles acting upon the levers of the skeleton. 

 I be morphology of the effector organ sets the me- 

 chanical conditions which limit the possibilities of 

 its use. from this point of view, man's hand is, .is 

 Galen saiel, ""a perfectly constructed instrument of 

 prehension." We owe to this author a penetrating 

 studv of the mechanical conditions of the act of 

 prehension. The essential morphological charac- 

 teristic of the hand of the primates and of man 

 resides in the rather complete mechanical inde- 

 pendence "i the live digital appendices which com- 

 pose it and --till more in the opposition ol the thumb. 

 Aristotle, who called it the 'great linger,' underlined 

 the functional importance of this arrangement. 

 Galen noticed, with exactitude, the advantage of 

 man's hand with its opposable thumb over the flat 

 hand ol the monkey . 



Thirty muscles arc employed in the movement ol 



the multiple joints o| the hand As sirewd bv Jack- 

 OH (ll6), they make possible the thousands ol 



binations ol movements which he believed to be 



'represented' in the eoi lev We must note especially 



with Gratiolei [cited bv .Mix (5)] the addition to the 



hand of a inusele belonging only to man, the long 



propei flexoi "I the thumb, the independent action 

 of which permits the isolated flexion oi the second 



phalanx and contributes to the execution of the 

 delicate movements of writing (28). 



Each contracting muscle generally exerts an 

 obvious mechanical effect which is due to its fixed 

 attachment to the bone lever. The arrangement of 

 muscles relative to the lever arms shows several 

 different types of organization. The most elementary 

 organization appears in the play of the hinge joint 

 articulations, the 'ginglymi' of Winslow (134), as 

 in the knee, elbow and interphalangeal joints. The 

 mobility of such a joint requires the insertion of two 

 muscles or muscle groups on opposite sides of the 

 bone lever (see lig. 2). The simultaneous action ol 

 these two muscles ('coinnervation' ) permits fixation 

 of an articulation and its maintenance in a deter- 

 mined position by means of a nonkinetogenic muscu- 

 lar activity (which had already been called 'tonic' bv 

 Galen). From the antagonistic action of these muscle-, 

 ('reciprocal innervation'!, one contracting while the 

 other relaxes, there results .1 movement ol the lever. 

 In relation to the natural position of rest of the lever 

 arm, we call the muscle the contraction of which 

 tends 10 augment the open angle of the articulation 

 an 'extensor,' and the one the action of which di- 

 minishes this angle a 'flexor.' 



The hinge joint articulations are, however, not 



the rule 1 lie joints of the segments of the limbs I 



ol their attachments to the skeletal girdles generally 

 posM-vs more than one degree oi freedom, the 'ar- 

 throdies' and 'enarthroses' of Winslow (134) \< 

 cordingly, they require lor their movement a more 

 complex muscular organization than the simple 

 antagonism just described. 



The 'ball joint' can, lor instance, be moved in any 

 direction whatSOevei around its center within its 



