. Electro-physiology . vin CONDUCTIVITY AND EXCITABILITY OF XERVE 101 tetanus. If the excitation is weakened again, the opposite effect occurs, /.c. the muscle relaxes. With the gradual disappearance of the tonic contraction, the visible excitation effects appear in one direction only, namely, closure of the claw, contraction of the muscle. The same thing of course follows in preparations where the adductor muscle from the first manifests no perceptible tonus. In correspondence with the characteristics of this muscle as cross- striated, the changes of form described take place with consid
. Electro-physiology . vin CONDUCTIVITY AND EXCITABILITY OF XERVE 101 tetanus. If the excitation is weakened again, the opposite effect occurs, /.c. the muscle relaxes. With the gradual disappearance of the tonic contraction, the visible excitation effects appear in one direction only, namely, closure of the claw, contraction of the muscle. The same thing of course follows in preparations where the adductor muscle from the first manifests no perceptible tonus. In correspondence with the characteristics of this muscle as cross- striated, the changes of form described take place with considerable rapidity. If they are graphically recorded on a slowly-moving surface (Fig. 167), the 11 , . , I , . , . I , . , . I , , curve sinks nearly at right angles at Flo. excitation of ad- the beginning of the tetanus, when the dllctor muscle of crayfish claw in 0 persistent tonic contraction; suc- niUSCle Undergoes SUdden and Often cession of brief inhibitions (relaxa- maximal relaxation. At that strength tion) at eac1'excitation of the nerve" of current with which the inhibitory excitation passes into its contrary, the effects are not seldom in both directions, and many irregularities are manifested. In cases where the natural tonus is wanting, the inhibitory effect of stimulating the nerve may sometimes be demonstrated if the relaxed and resting muscle is artificially thrown into persistent or rhythmically interrupted excitation. This is easily effected by including a metronome in the secondary circuit, as well as the vibrating hammer of the coil, so that groups of induction shocks at any required rhythm may be sent into the adductor muscle by means of two platinum points thrust through the chitinous sheath of the claw. Eegular rhythmical contractions are thus produced, which can be affected by simultaneous excitation of the nerve in the same way as the natural heart-beat, by excitation of the vagus. If, in the preparation in question, the adductor muscle
Size: 3669px × 1362px
Photo credit: © The Bookworm Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1800, bookdecade1890, bookpublisherlondonmacmillan
