. The biology of marine animals. Marine animals; Physiology, Comparative. 110 THE BIOLOGY OF MARINE ANIMALS Raja) (Fig. ). There is occasionally an initial inhibitory effect, which is blocked by atropine. The effect of these amines on the teleost heart is slight (6, 19, 60, 97). Molluscan hearts are myogenic, and all regions can show autonomous contractions. During contraction there is a well-marked A-V interval, amounting to about 0-5 sec. Electrocardiograms have been recorded from several mulluscan hearts, and show the slow waves characteristic of myo- genic types. In Octopus there is an
. The biology of marine animals. Marine animals; Physiology, Comparative. 110 THE BIOLOGY OF MARINE ANIMALS Raja) (Fig. ). There is occasionally an initial inhibitory effect, which is blocked by atropine. The effect of these amines on the teleost heart is slight (6, 19, 60, 97). Molluscan hearts are myogenic, and all regions can show autonomous contractions. During contraction there is a well-marked A-V interval, amounting to about 0-5 sec. Electrocardiograms have been recorded from several mulluscan hearts, and show the slow waves characteristic of myo- genic types. In Octopus there is an initial fast deflexion succeeded by a prolonged wave of negativity, and the same sort of pattern is shown by the gill heart of Lo/igo. The electrocardiogram of Aplysia consists of slow waves with superimposed irregular deflexions; those of bivalves (Ostrea, Anodontd) normally display a diphasic component near the beginning of. -*&-*&- (a) (b) Fig. Electrocardiograms of Molluscan Hearts (a). Aplysia. From above downwards, myogram, electrocardiogram, time in seconds (from Hoffmann, 1911.) (b). Crassostrea virginica. Electrical record, small waves; mechanical tracing, large waves. Upward deflexion of myogram indicates contraction. Time scale below, 1 sec. Temp. 22°C (from Taylor and Walzl (126).) contraction and one or several slow waves associated with contraction (Fig. ). Apparently the fast component in the ECG represents the spread of excitation; and the slow waves, potential changes taking place during contraction. Although showing automaticity, the hearts of molluscs are subject to nervous regulation. Cardiac nerves arise from the visceral ganglion in lamellibranchs; the presence of nerve cells in the heart is disputed. In gastropods cardiac nerves arise from the visceral or accessory visceral ganglion, and terminate in auricle and ventricle. The existence of nerve cells is in doubt; if present they probably represent secondary regulatory neurones. The ne
Size: 1367px × 1829px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectmarineanimals, booksubjectphysiology
