frog heart study

frog heart study - Na Hye Eunice Kim MCB 32L (THURS-Keling...

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Na Hye Eunice Kim MCB 32L (THURS-Keling Chen) 5 November 2009 LAB7: Frog Heart Study I. Introduction Background: Amphibian like frog has four chambers: the sinous venosus, two atria, and a ventricle. Unlike human heart, frog heart has only one ventricle, causing some mixing of oxygenated and deoxygenated blood, but the structure of the ventricle and the presence of a spiral valve in the arterial cone sufficiently separate the blood. The heart is made up of its muscle layer called myocardium. These myocardial cells are joined to each other by intercalated discs with desmosomes and gap junctions. Desmosomes hold cells together during heart contraction and swelling, and gap junctions allow the passage of molecules and waves of depolarization to spread over the myocardium by using the ion channels. The action potential produced by the pacemaker cells spreads to neighboring cells result in contraction of muscle cells in the atria and in the ventricle. The mechanism of propagation of the action potential in the heart is similar to propagation along an axon. The major difference is that the action potential spreads from one cell to another through gap junctions. In addition, in cardiac muscle, calcium rises because of calcium coming in from extracellular space as well as from the sarcoplasmic reticulum within the cell. Depolization in cardiac muscle is longer than that of skeletal muscle, resulting in a longer absolute and relative refractory period which stops myocardial tetanus from occurring. Similar to the mammalian heart, the number of impulses that arises from pacemaker in the sinus venosus is influenced by sympathetic and parasympathetic nerves, temperature, chemical agents, and other factors. For example, Through vagus nerve, the parasympathetic releases acetylcholine which decrease heart rate. On the other hand, the sympathetic innervations release norepinephrine, which increases heart rate. Epinephrine is more like norepinephrine, increasing the heart rate. The purpose of this lab is to examine the characteristics of cardiac muscle by using many different parameters. Direct heart stimulation, vagus nerve stimulation, and the influence of neurotransmitters, temperature, and ions on cardiac muscle are studied. Hypothesis : In the trace of normal heartbeat, there will be two rises: smaller rise for atrial contraction and larger rise for ventricular contraction. When the heart is stimulated, extra ventricular systole will result. Warm ringers will speed up the heart while cold ringers will slow down the heart. Epinephrine will speed up the heart and acetylcholine will slow down the heart. An excessive potassium and calcium ions in the extracellular environment reduces heart rate as well as the strength of contraction. II.
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frog heart study - Na Hye Eunice Kim MCB 32L (THURS-Keling...

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