Uncoordinated atrial and ventricular contractions 3

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Uncoordinated atrial and ventricular contractions3.Fibrillation: rapid, irregular contractions; useless for pumping blood
Extrinsic Innervation of the HeartHeartbeat is modified by the ANS Cardiac centers are located in the medulla oblongataCardioacceleratory center innervates SA and AV nodes, heart muscle, and coronary arteries through sympathetic neuronsCardioinhibitory center inhibits SA and AV nodes through parasympathetic fibers in the vagus nerves
Figure 18.15Thoracic spinal cordThe vagus nerve (parasympathetic) decreases heart rate.Cardioinhibitory centerCardio-acceleratorycenterSympathetic cardiacnerves increase heart rateand force of contraction.Medulla oblongataSympathetic trunk ganglionDorsal motor nucleus of vagusSympathetic trunkAV nodeSA nodeParasympathetic fibersSympathetic fibersInterneurons
ElectrocardiographyElectrocardiogram (ECG or EKG): a composite of all the action potentials generated by nodal and contractile cells at a given timeThree waves1.P wave: depolarization of SA node2.QRS complex: ventricular depolarization3.T wave: ventricular repolarization
Figure 18.16SinoatrialnodeAtrioventricularnodeAtrialdepolarizationQRS complexVentriculardepolarizationVentricularrepolarizationP-QIntervalS-TSegmentQ-TInterval
Figure 18.18(a) Normal sinus rhythm.(c) Second-degree heart block.Some P waves are not conductedthrough the AV node; hence more P than QRS waves are seen. In this tracing, the ratio of P waves to QRS waves is mostly 2:1.(d) Ventricular fibrillation. Thesechaotic, grossly irregular ECGdeflections are seen in acuteheart attack and electrical shock.(b) Junctional rhythm. The SA node is nonfunctional, P waves are absent, and heart is paced by the AV node at 40 - 60 beats/min.
Heart SoundsTwo sounds (lub-dup) associated with closing of heart valvesFirst sound occurs as AV valves close and signifies beginning of systoleSecond sound occurs when SL valves close at the beginning of ventricular diastole Heart murmurs: abnormal heart sounds most often indicative of valve problems
Figure 18.19Tricuspid valve sounds typically heard in right sternal margin of 5th intercostal spaceAortic valve sounds heard in 2nd intercostal space atright sternal marginPulmonary valvesounds heard in 2ndintercostal space at leftsternal marginMitral valve soundsheard over heart apex(in 5th intercostal space)in line with middle ofclavicle
Mechanical Events: The Cardiac CycleCardiac cycle: all events associated with blood flow through the heart during one complete heartbeatSystole—contraction Diastole—relaxation
Phases of the Cardiac Cycle1.Ventricular filling—takes place in mid-to-late diastoleAV valves are open 80% of blood passively flows into ventriclesAtrial systole occurs, delivering the remaining 20%End diastolic volume (EDV): volume of blood in each ventricle at the end of ventricular diastole
Phases of the Cardiac Cycle2.

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