File:A text-book of physiology - for medical students and physicians (1916) (14583518919).jpg

Identifier: textbookofphysio1916howe (find matches)
Title: A text-book of physiology : for medical students and physicians
Year: 1916 (1910s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Medicine
Publisher: Philadelphia and London : W. B. Saunders Company
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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sses inthe nerve and their effect upon the muscle may be studied simul-taneously. Relation of the Action Current to the Contraction Wavein Muscle and to the Excitation Wave (Nerve Impulse) in Nerve.—The action current or, to be more accurate, the moving negativepotential, which gives rise to an action current when two pointsof the muscle are led off to a galvanometer, has been shown 106 THE PHYSIOLOGY OF MUSCLE AND NERVE. by Bernstein to precede the wave of contraction in muscle; thatis, in a stimulated muscle fiber the electrical change at any pointprecedes the mechanical process of shortening. This relation-ship is shown in the accompanying illustration (Fig. 48), in whichthe mechanical contraction (movement of the lever) is photo-graphed simultaneously with the movement of the string of thestring-galvanometer which indicates the electrical change. Asthe figure shows the electrical change is diphasic, owing to the op-posite effects on the galvanometer of the change of potential at
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Fig. 48.—Simultaneous record of the mechanical and electrical change in a contractingmuscle: 1, Mechanical curve of contraction, photograph of the lever; 2, movement of thestring of the string-galvanometer (owing to its faintness it was necessary to retouch thiscurve); movement upward indicates an increase of negative potential at the upper end of themuscle; 3, time record in hundredths of a second; 4, the stimulating lever; the break in theline indicates the moment of stimulation; on the curve of contraction (1) this moment isindicated by x; on the curve showing the movement of the string (2) the same instant ismarked by the small nick in the curve preceding the large wave caused by the electricalchange. The curve was obtained from the gastrocnemius muscle of a frog, stimulatedthrough its nerve by a single induction shock, contraction isotonic. The leading-off electrodeswere placed at the ends of the muscle; galvanometer string under tension. The electric curveis diphasic, and both

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