MTSCLE-KERVE. 



XVI. To DETERMINE ACTUAL SHORTENING OF A MUSCLE 



LN CONTRACTION. 



Divide distance of the writing point of the muscle lever from the 

 axis of the lever by the distance of the muscle attachment from the 

 axis. Then divide the height of the recorded curve by thi> factor. 

 The result is the actual shortening of the muscle during con- 

 traction. 



XVII . To DETERMINE THE WORK DONE BY THE MUSCLE dur- 

 ing any particular contraction, multiply the actual shortening by 

 the load. Thus, if the actual shortening or height of contraction is 

 5 millimetres and the load is 10 grams, then the work done would 

 be 50 gram-millimetres, 



1. On a drum revolved by hand, record the heights of contrac- 

 tion of a gastrocnemius which is receiving submaximal stimuli. 

 After-load the muscle successively with 10, 20, 30. 40, 50, 70, 100, 

 150, 200, 250, 300. 350, 400, 450, and 500 grams. 



2. Estimate the actual work done according to the formulae 

 given above. Plot a curve, marking, on the abscissa, intervals to 

 represent 50-gram weights; on the ordinates, intervals to repre- 

 sent gram-millimetres. What conclusions can you draw from the 

 data thus plotted ? 



XVIII. FATIGUE OF HUMAN VOLUNTARY MUSCLE. 



Ergography. The contraction of voluntary muscle is normally 

 brought about through nerve impulses originating in nerve cells. 

 The nerve cell, as will be shown later, has a certain rhythmic ac- 

 tivity, sending out from 6 to 10 impulses per second. This seems 

 to be sufficient to keep the muscle in a state of tetanus. The short- 

 est voluntary muscle contraction, then, brought about through the 

 discharge of nerve impulses from nerve cells, is a tetanus. The 

 single twitch occurs only under abnormal circumstances, or through 

 artificial stimulation of the nerve or muscle directly. Any stimu- 

 lation of nerve cells, sufficient to cause a discharge of nerve im- 

 pulses, will produce a tetanus in the muscle receiving the impulses. 



