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In what ways are autorhythmic fibers similar to and different from contractile...

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lashsh | Student, College Freshman | (Level 2) Honors

Posted August 3, 2010 at 11:59 AM via web

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In what ways are autorhythmic fibers similar to and different from contractile fibers?


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chimeric | College Teacher | (Level 2) Adjunct Educator

Posted August 13, 2010 at 3:53 AM (Answer #1)

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The source of the rhythmical electrical activity that makes up the heart's lifelong beat is found in autorhytmic fibers. These fibers "repeatedly generate action potentials that trigger heart contractions. They continue to stimulate a heart to beat even after it is removed from the body," because unlike contractile fibers, they are self excitable and do not require neural stimulation to trigger contractions. "Autorhythmic fibers form the conduction system, cardiac muscle fibers that spontaneously depolarize and generate action potentials." (p. 726)

Unlike autorhythmic fibers, contractile
fibers have a stable resting membrane potential that is close to - 90 mV. When a contractile fiber is brought to threshold by an action potential from neighboring fibers, its voltage-gated fast Na+ channels open. (p. 728)

Source: Anatomy and Physiology: From Science to Life, 2nd Edition Gail Jenkins (Montgomery College ), Christopher Kemnitz (Lake Superior College ), Gerard J. Tortora (Bergen Community College) January 2009, ©2010

Chapter 20: The Cardiovascular System: The Heart


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