18. Cardiovascular System: the Heart

Action potentials in cardiac pacemaker and contractile cells

Heart Physiology: Electrical Events

Cardiac Action Potential

 AV node, subendocardial conducting network, AV node, AV bundle, right and left bundle branches 

 Impulses generated by the SA node spread to the AV node, then to the AV bundle, then to the bundle branches, and finally to the subendocardial conducting network (Purkinje fibers). 

 SA node, subendocardial conducting network, AV node, AV bundle, right and left bundle branches 

 SA node, AV node, AV bundle, right and left bundle branches, subendocardial conducting network 

 subendocardial conducting network, AV node, AV bundle, right and left bundle branches, SA node 

 AV node, SA node, subendocardial conducting network, AV bundle, right and left bundle branches 

 Choose the correct sequence of electrical current flow through the heart wall. 

Intrinsic Conduction System of the Heart

 heart block: uncoordinated atrial and ventricular contraction 

 Extrasystole, or premature contraction, can be caused by ectopic or abnormal pacemakers (also called ectopic foci). An ectopic focus can result when the sinoatrial (SA) node is defective. Additionally, some substances (such as caffeine and nicotine) consumed in excess can generate an ectopic focus. Any defect in the intrinsic conduction system of the heart can generate an irregular heart rhythm (an arrhythmia). Damage to the atrioventricular (AV) node can lead to a heart block. In a complete heart block, impulses do not reach the ventricles; as a result, the ventricles beat at their intrinsic rate, which is too slow to maintain adequate circulation. Fibrillation is characterized by rapid and irregular or out-of-phase contractions of the heart chambers. 

 arrhythmia: atrioventricular (AV) node failure  

 Which of the following are correctly paired? 

 subendocardial conducting network (Purkinje fibers) 

 The SA node generates impulses faster than the other node and sets the pace for the heart. 

 The normal pacemaker of the heart is the __________. 

Cardiac Muscle Action Potential Diagram

Heart: Excitation-Contraction Coupling

 Repolarization abnormalities are represented by a prolonged Q-T interval on an ECG. An enlarged ventricle would appear as an enlarged R wave on an ECG. 

 A myocardial infarction would appear as elevation of the S-T segment on an ECG. An enlarged ventricle would appear as an enlarged R wave on an ECG. 

 An elevated S-T segment on an ECG indicates cardiac ischemia. An enlarged ventricle would appear as an enlarged R wave on an ECG. 

 An enlarged R wave on an ECG would indicate __________. 

EKG/ECG Interpretation

 Pacemakers are noncontractile cardiac muscle cells with an unstable resting membrane potential. 

 The noncontractile cardiac muscle cells that initiate their own depolarization and cause depolarization of the rest of the heart are called __________. 

 The P wave reflects the depolarization of the atria. The QRS complex shows ventricular depolarization, and the T wave is generated by ventricular repolarization. Since the QRS complex is so large, it obscures the wave that is generated by atrial repolarization.  

 The P wave of an electrocardiogram represents __________. 

 The vagus nerve carries parasympathetic fibers to the SA node. 

 The __________ nerve carries parasympathetic fibers to the sinoatrial (SA) node. 

IP Intrinsic Conduction System of the Heart

 An impulse of the heart originates at the sinoatrial (SA) node. The impulse is then transmitted to the atrioventricular (AV) node, where the impulse slows down to allow the atria to completely contract, thereby filling the adjacent ventricles. The AV node then transmits the impulse to the atrioventricular bundle (bundle of His), which branches into left and right bundle branches. The bundle branches give rise to the subendocardial conducting network (Purkinje fibers), which transmit the impulse to the ventricle walls and stimulate ventricular contraction.  

 slow down impulses so that the atria can contract to fill the adjacent ventricles with blood 

 conduct impulses to the sinoatrial node (SA node) 

 The role of the atrioventricular node (AV node) is to __________.  

 the muscle cell will not respond to a stimulus of any strength 

 the muscle cell will respond only to an exceptionally strong stimulus 

 During the absolute refractory period, a muscle cell will not respond to a stimulus of any strength. 

 the muscle cell is ready to respond to any stimulus 

 the muscle cell will respond only to a sub-threshold stimulus 

 the muscle cell is ready to respond to a threshold stimulus 

 The absolute refractory period refers to the time during which __________. 

Action Potentials in Autorhythmic Cells

EKG - Abnormal Heart Rhythms

Cardiac Conduction System

Electrical Conduction System of the Heart Cardiac

Conducting System of the Heart

Cardiac Conduction System and Understanding ECG

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1. Introduction to A&P

2. Chemistry

3. Cells

4. Tissues

5. Integumentary System

6. Bones + Skeletal Tissues

7. Skeletal System

8. Joints

9. Muscles and Muscle Tissue

10. Muscular System

11. Nervous Tissue

12. Central Nervous System

13. Peripheral Nervous System

14. Autonomic Nervous System

15. Special Senses

16. Endocrine System

17. Blood

19. Cardiovascular System: Blood Vessels

20. Lymphatic System

21. Immune System

22. Respiratory System

23. Digestive System

24. Nutrition, Metabolism, Energy Balance

25. Urinary System

26. Fluid and Electrolyte Balance, Acid Base Balance

27. Reproductive System

28. Pregnancy and Human Development