. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Muscle and Electric Origans 603 contract when distended (Ch. 15, p. 547). In vivo hormonal agents, par- ticularly acet\lcholine and adrcnin, are also important in regulating smooth muscle tone. Local, non-conducted impulses from a "pacemaker" region may result in tonus in an organ such as the '- Between these two extremes of striated skeletal and the smooth muscle of hollow organs are many muscles in which rapid rcHex responses may be superimposed upon a tonic background intrinsic in the muscle
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Muscle and Electric Origans 603 contract when distended (Ch. 15, p. 547). In vivo hormonal agents, par- ticularly acet\lcholine and adrcnin, are also important in regulating smooth muscle tone. Local, non-conducted impulses from a "pacemaker" region may result in tonus in an organ such as the '- Between these two extremes of striated skeletal and the smooth muscle of hollow organs are many muscles in which rapid rcHex responses may be superimposed upon a tonic background intrinsic in the muscle. Squid chro- matophore muscles, for example, show a tonic state upon which twitches are super]:);'' Relaxation curves of numerous molluscan and mammalian smooth muscles are similar to the curves of release of tension after a stretch (Fig. 232).^"- ^' However, if in addition the muscle develops tonus on. Fig. 233. Responses ot the byssus retractor ot Mytilus to stimulation with alternating current and direct current. A, Three contractions in response to stimulation by AC (50 cps) for 10 sec. each, and response to stimulation by DC for 10 sec. B, Response to AC 14 sec. tor each minute. C, Response to DC 14 seconds per minute. Note delayed relaxation, summation with DC, fast relaxation and fatigue with AC. After ;"*' Stretching, the relaxation from a contraction may be faster than release of tension.^â '*- '"'' |ordan and his students in many papers, summarized by Jor- dan,^'"' have shown that tonus in the molluscan foot is in part a response of the muscle to stretch but is regulated by the nervous system. It is sug- gested that the tonic and contractile mechanisms are separate. The pedal ganglion decreases the resistance to stretching but does not affect the con- tractility of the foot to an electrical stimulus, whereas the presence of the cerebral ganglion is said to increase the contractility without having any. Please note that these
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