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Contents of the Cardiac Cycle of the Turtle

bulletEffects of Temperature
bulletNature of the Refractory Period
bulletStarling's Law of the Heart
bulletEffects of Vagal Stimulation

Details of the Cardiac Cycle of the Turtle

The second program deals with the events of the cardiac cycle and the intrinsic and extrinsic factors that control it. The tape begins by comparing the human heart to that of a turtle with respect to the origin of the pacemaking impulse and the rhythmic activity of pacemaker cells. Gross differences in the structure of the human and turtle heart are discussed.

The next segment of the tape demonstrates the turtle heart preparation itself and shows the external anatomy of the turtle heart. The tape demonstrates the attachment of transducers to record the atrial and ventricular myograms. The equipment utilized in the recording of the experimental variables is discussed and includes a Tektronix model 5113 dual beam, dual trace storage oscilloscope, two Harvard model 357 heart muscle transducers and a Grass model S-44 stimulator. The nature and time course of a myogram are discussed and the atrial and ventricular myograms are displayed on the storage scope.

The third segment of the tape examines the effects of temperature on heart rate followed by a demonstration of Starling's Law of the heart. The nature of the refractory period of cardiac muscle is explored by stimulation at different times during the cardiac cycle. The terms extra systole and compensatory pause are discussed and correlations are made with Starling's Law. Correlations between the physical and electrical events of the cardiac cycle are demonstrated next by simultaneous recordings of the atrial and ventricular myograms and of the electrocardiogram.

The tape illustrates the dissection of the vagus nerve preparatory to vagal nerve stimulation. The tape concludes by presenting the effects of vagal stimulation on heart rate. Inhibition followed by ventricular escape is shown. A data readout of the physiological information accompanies each of the sections and involves two or three channels of data.


February 08, 2001

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Last modified:    02/08/01