Essentials of human physiology for medical students / by D. Noël Paton.

  • Paton D. No︠︡l (Diarmid No︠︡l), 1859-1928.
Date:
1903
Catalogue details

Licence: In copyright

Credit: Essentials of human physiology for medical students / by D. Noël Paton. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    for a time by washing out the muscle with salt solution (Fig. 20). {Practical Exercise.) 2. Temperature.—U a muscle be warmed above the nor- mal temperature of the animal from which it is taken, all the phases of contraction become more rapid, but the contraction is less complete and less powerful. If, on the other hand, a muscle be cooled, the various periods are prolonged. At first the contraction hecomes greater and more powerful, but as the cooling process goes on, it becomes less and less, until finally the most powerful stimuli produce no effect. Cooling has thus practically the same effect as fatigue (Fig. 20). {Practical Exercise.) 4. Strength of Stimulus.—A stimulus must have a certain intensity to cause a contraction. The precise strength of this minimum stim- ulus depends upon the condition of the muscle. The appli- cation of stronger and stronger stim- uli cause the muscu- lar contraction to become more and more rapid, more and more complete, and more and more powerful. But in- crease in the contraction is not proportionate to the increase in the stimulus. If the stimulus is steadily increased, the increase in contraction becomes less and less. This may be represented diagrammatically in the accompany- ing figure where the continuous line represents the strength of the stimulus and the dotted line the extent of the con- traction (Fig. 21). After a certain strength of stimulus has been reached, further increase of the stimulus does not cause any increase in the muscular contraction. This smallest stimulus which causes the maximum muscular contraction is called the optimum stimulus. Fig. 21.—Influence of increasing the Strength of Stimulus upon the contraction of Skeletal Muscle. St., the stimulus ; Con., the resulting contraction. A, A subminimal stimulus ; B, The minimum adequate stim- ulus ; C, The optimum stimulus.