AbstractCineradiography and electromyography were used to study the strike and swallowing behaviour of the rattlesnake, Crotalus durissus. From the data gathered, we describe the kinetic events of the cranial bones correlated with both the activity of individual jaw muscles (electromyograms) and with the calculated relative forces produced by these same muscles. During the strike, the independently suspended jaws of left and right sides simultaneously protract to erect the folded fangs. This is accompanied by opening of the lower jaws. Some low level activity first appears in the depressor muscles, but immediately thereafter they and all other jaw muscles suddenly and nearly simultaneously reach peak output. From the calculated relative muscle forces, vector models of the jaws were determined for early and peak points in the strike. Swallowing is accomplished by reciprocating alternate motions of bones on the left and right sides of the skull. This produces a swallowing cycle of two phases, moving and fixing. In turn, each phase divides into three parts-opening, advance, close. On the ipsilateral side, opening is characterized by a relaxation of contact of bones and teeth they bear with the prey and the braincase begins rotation about three axes simultaneously. Motions begun in opening, contiue into advance, but now the ipsilateral jaw elements are protracted to progress them along the prey. As protraction ends, the jaws again come into contact with the prey to establish the close part of the moving phase of swallowing. After a pause, the fixing phase begins while opposite jaw elements now take their turn to progress through similar displacements. During this fixing phase ipsilateral elements arc often further retracted. Emphasis is given to the complicated rotations of the braincase which contribute first to disengagement of teeth and second to advancement of suspended jaw elements around and along the prey. Most muscles reached peak output during one of the two swallowing phases, although the timing and intensity of these peaks varied between muscles. The relative muscle forces were used to construct vector models of the jaws during stages of swallowing. Upon these vector models and from the overall patterns of activity, determination was made of the likely roles played by individual muscles in abduction, protraction, and adduction of jaw elements. Muscles, besides being basic movers of the jaw elements, apparently also play critical parts in stabilizing and regulating the controlled positioning of bones.
Bimanual Movements and Chronic Stroke Rehabilitation: Looking Back and Looking Forward
