A text-book of human physiology (1906) (14583726970)

Identifier: textbookofhumanp00tige (find matches)

Title: A text-book of human physiology

Year: 1906 (1900s)

Authors: Tigerstedt, Robert, 1853-1923 Murlin, John R. (John Raymond), b. 1874, tr

Subjects: Physiology

Publisher: New York and London, D. Appleton and Co.

Contributing Library: Columbia University Libraries

Digitizing Sponsor: Open Knowledge Commons

Text Appearing Before Image:

fibers.The red salens muscle of the rabbit falls into almost complete tetanus with tenstimuli per second, while the white (fastrncnemius medius with the same fre-quency of stimulation gives very evidf^it single contractions. A frequency ofsix stimuli per second permits the white muscle to relax almost completely 430 THE FUNCTIONS OF CROSS-STRIATED MUSCLES between contractions, whereas it keeps the red muscle almost continuously con-tracted (Ranvier, Kronecker and Stirling; cf. Fig. 167). Everything which tends to make the single contractions occupy more timeoperates to reduce the frequency of stimulation necessary to evoke completetetanus. Thus fatigued muscles are thrown into tetanus with a lower frequencythan unfatigued, because their contractions are slower. The more the frequency is reduced below that which is just sufficient toproduce tetanus, the more distinctly do the contractions produced by the indi-vidual stimuli stand out from one another, until finally below a certain fre-

Text Appearing After Image:

FiG. 167.—Tetanus curves of the white (lower tracings) and of the red (upper tracings) musclesof the rabbit, after Kronecker and Stirling. To be read from right to left. A. ten stimuliper second. B, six stimuli per second. quency there is no fusion whatever. We have therefore all possible gradationsbetween the isolated contractions and complete tetanus. This suggests that teta-nus itself, notwithstanding the continuous curve by which it is representedgraphically, is really a discontinuous process, and complete proof of this isfurnished by the electrical variations accompanying tetanus (page 433). How are we to conceive of the processes going on in the muscle in tetanus?One significant fact is that by artificially supporting the muscle, so that it doesnot lift its weight until it has contracted some distance, the single contractionscan be made to reach the same height as tetanus with the same strength of cur-rent (v. Frey). We may say, therefore, that in tetanus the muscle contractst

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1906

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