LESSON VIII 

 MUSCLE AND NERVE (Continued) 



CONDUCTION IN NERVE. ACTION CURRENT OF MUSCLE AND NERVE, 

 STIMULATION OF MOTOR POINTS 



1. Motor Nerve More Irritable Near its Center. Pith a frog. 

 Expose . the sciatic nerve in two places, namely : (a) in the pelvis by 

 an incision between the urostyle and the ilium, and (6) in the thigh 

 (dorsal) near the gastrocnemius muscle. Insulate both segments care- 

 fully by means of narrow strips of rubber membrane. Arrange the 

 electric apparatus for stimulation with single induction shocks and de- 

 termine the least strength of make or break shocks which will give a 

 contraction in these two places. Compare the results. 



2. Influence of Temperature. Isolate the nerve just used in its 

 entire length, and place it upon a layer of cotton moistened with warmed 

 saline solution (40 to 45 C.). Apply the electrodes to this stretch of 

 nerve, and determine the threshold value of the make shock now re- 

 quired to evoke a contraction of the gastrocnemius muscle. Quickly 

 place the nerve upon a piece of ice, and again determine the threshold of 

 the least effective make shock. , Compare the results. 



3. Galvani's Experiment. Destroy the brain of a frog and cut away 

 the forepart of its body. Also remove the viscera, ilium, and urostyle, 

 but without injuring the roots of the sciatic nerves. The latter then 

 form the only connection between the lower end of the spinal cord and 

 the legs. Remove the skin from the latter and pass a copper hook 

 through the spinal segment. Suspend this preparation from an ordi- 

 nary iron tripod. Tilt the latter so that the legs come in contact with 

 the iron. Vigorous contractions will result whenever the legs touch the 

 iron. Explain, giving Galvani's as well as Volta's view. 



4. Action Current of Muscle. Rheoscopic Frog. Prepare two 

 gastrocnemii muscles with long segments of nerve. Place both upon 

 a plate at some distance from one another, allowing the end of nerve A 

 to rest upon the raised electrodes, and nerve B of the other muscle 

 lengthwise upon muscle A. Moisten this preparation with saline, but 

 do not allow any of this solution to flow upon the plate. Arrange the 

 induction coil for stimulation with quickly repeated shocks. Stimulate 

 nerve A briefly, noting that muscle B reacts simultaneously with 

 muscle A. 



Annotation. The impulses set up in nerve A by the stimulation produce a 

 contraction of muscle A. Since the different segments of this muscle do not react 

 simultaneously but successively, certain segments of it must be at rest and others 

 active. The active ones are galvanometrically negative to the resting ones, and 

 hence a difference in electric potential is set up in this muscle which is sufficient to 



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