Reflex Contractions 



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237 (2197) 



Reflex contractions of an all-or-none character. 

 By EUGENE L. PORTER and VICTOR V/. HART (by invitation). 



[From the Department of Physiology, School of Medicine, Western 

 Reserve University, Cleveland, Ohio.] 



Sherrington's emphasis on the differences between reflex arc 

 conduction and conduction in the nerve trunk has long been 

 familiar to physiologists. With the establishment of the all-or- 

 none law for muscle and for nerve in recent years it was but 

 natural that the query should be raised as to whether reflex 

 action be bound by the limitations of the all-or-none behavior 

 of muscle and of nerve, or whether the central nervous system 

 so alters the final nerve impulse to muscle that it can over-ride 

 these limitations. A single sensory impulse, for example, might 

 always result in a volley of impulses along the final motor 

 neurones, according to Sherrington's suggestion. 1 Variations 

 in the number of impulses comprising this volley might, by sum- 

 mation of contractions, conceivably produce in the muscle de- 

 grees of response of almost any grade of fineness, and reflex 

 contractions would not then show an all-or-none character. 



The present research was undertaken with the object of com- 

 paring minimal, or close to minimal, responses of muscle se- 

 cured by single shocks to its motor nerve, with similar responses 

 obtained reflexly by stimulation of a sensory nerve. 



The muscle employed was the tenuissimus, a long slender, 

 straight-fibered muscle underlying the biceps and containing 

 approximately one thousand fibers. 2 The nerve to this muscle 

 contains about twenty motor neurones, each neurone presumably 

 innervating approximately fifty muscle fibers. If this nerve 

 be stimulated by single shocks gradually increasing in strength 

 the response of the muscle is not gradual, but by step-like incre- 

 ments, there being no gradation between one step and the next. 

 The heights of the first three increments to appear in three of such 

 experiments are shown in Experiments I, II and III of the ap- 

 pended table. The response is of the same character as that 

 observed by Lucas 3 in the dorso-cutaneous nerve muscle prepa- 

 ration in the frog. When the appropriate sensory nerve is sim- 



1 Sherrington, Proc. Boy. Soc, 1921, xcii, B, 245. 



2 Graham Brown, Proc. Boy. Soc, 1914, lxxxvii, B, 132. 



3 Lucas, Jour. Phys., 1905, xxxiii, 125. 



