1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 18 The Cardiovascular System: The Heart: Part B

2. Copyright © 2010 Pearson Education, Inc. The conductive system The heart is an autonomic system that can work without neural stimuli – an intrinsic conduction system. The autonomic function of the heart results from: The pacemaker function – Autorhythmic cells The conductive system that transfer those impulses throughout the heart Two types of cardiac muscle cells that are involved in a normal heartbeat: Specialized muscle cells of the conducting system Contractile cells

3. Copyright © 2010 Pearson Education, Inc. Heart Physiology: Sequence of Excitation 1.Sinoatrial (SA) node (pacemaker) Generates impulses about 75 times/minute (sinus rhythm) Depolarizes faster than any other part of the myocardium 2.Atrioventricular (AV) node Smaller diameter fibers; fewer gap junctions Delays impulses approximately 0.1 second Depolarizes 50 times per minute in absence of SA node input

4. Copyright © 2010 Pearson Education, Inc. Heart Physiology: Sequence of Excitation 3.Atrioventricular (AV) bundle (bundle of His) Only electrical connection between the atria and ventricles 4.Right and left bundle branches Two pathways in the interventricular septum that carry the impulses toward the apex of the heart 5.Purkinje fibers Complete the pathway into the apex and ventricular walls AV bundle and Purkinje fibers depolarize only 30 times per minute in absence of AV node input

5. Copyright © 2010 Pearson Education, Inc. The upper part of the heart (the 2 atria) is insulated from the lower part Electrical excitation can pass from the atria to the ventricles only at the AV node

6. Copyright © 2010 Pearson Education, Inc. Electrocardiography (ECG or EKG) Body fluids are good conductors which allows the record of the myocardial action potential extracellularly EKG pairs of electrodes (leads) one serve as positive side of the lead and one as the negative Potentials (voltage) are being measured between the 2 electrodes EKG is the summed electrical potentials generated by all cells of the heart and gives electrical “view” of 3D object (different from one action potential) EKG shows depolarization and repolarization

7. Copyright © 2010 Pearson Education, Inc. Electrocardiography EKG is made of waves and segments Waves are deflections above or below baseline Three waves 1.P wave: depolarization of SA node 2.QRS complex: ventricular depolarization (Atrial repolarization record is masked by the larger QRS complex) 3.T wave: ventricular repolarization Segments are sections of baseline between waves

8. Copyright © 2010 Pearson Education, Inc. An Electrocardiogram Figure 20.14b

9. Copyright © 2010 Pearson Education, Inc. Heart Sounds Two sounds (lub-dup) associated with closing of heart valves First sound occurs as AV valves close and signifies beginning of systole Second sound occurs when SL valves close at the beginning of ventricular diastole Heart murmurs: abnormal heart sounds most often indicative of valve problems