Cardiovascular System The Heart part 2

Cardiovascular System The Heart part 2 - Cardiovascular...

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Cardiovascular System: The Heart Angela Peterson-Ford, PhD September 15, 2010 Office: E 209 apetersonford@collin.edu
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18 The Cardiovascular System: The Heart Part 2
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Cardiac Muscle Contraction Heart muscle: Is stimulated by nerves and is self-excitable (automaticity) Contracts as a unit Has a long (250 ms) absolute refractory period Cardiac muscle contraction is similar to skeletal muscle contraction
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Heart Physiology: Intrinsic Conduction System Autorhythmic cells: Initiate action potentials Have unstable resting potentials called pacemaker potentials Use calcium influx (rather than sodium) for rising phase of the action potential
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Pacemaker and Action Potentials of the Heart Figure 18.13
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Heart Physiology: Sequence of Excitation Sinoatrial (SA) node generates impulses about 75 times/minute Atrioventricular (AV) node delays the impulse approximately 0.1 second Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)
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Heart Physiology: Sequence of Excitation AV bundle splits into two pathways in the interventricular septum (bundle branches) Bundle branches carry the impulse toward the apex of the heart Purkinje fibers carry the impulse to the heart apex and ventricular walls
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Heart Physiology: Sequence of Excitation Figure 18.14a
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Heart Excitation Related to ECG Figure 18.17
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Extrinsic Innervation of the Heart Heart is stimulated by the sympathetic cardioaccelerator y center Heart is inhibited by the parasympathetic cardioinhibitory center Figure 18.15
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Electrocardiography Electrical activity is recorded by electrocardiogram (ECG) P wave corresponds to depolarization of SA node
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Cardiovascular System The Heart part 2 - Cardiovascular...

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