R E V I E W S H E E T EXERCISE 31 > Conduction System of the Heart and Electrocardiography The Intrinsic Conduction System 1. List the elements of the intrinsic conduction system in order, starting from the SA node. SA node > ATRIOVENTRICULAR (AV) NODE > > ATRIOVENTRICULAR (AV) BUNDLE BUNDLE BRANCHES PURKINJE FIBERS ATRIOVENTRICULAR (AV) NODE At what structure in the transmission sequence is the impulse temporarily delayed? Why? THIS DELAY IS IMPORTANT BECAUSE IT ENSURES THAT THE ATRIA HAVE
EJECTED THEIR BLOOD INTO THE VENTRICLES FIRST BEFORE THE VENTRICLES CONTRACT. 2. Even though cardiac muscle has an inherent ability to beat, the nodal system plays a critical role in heart physiology. What is that role? GENERATE ACTION POTENTIALS AT A GREATER FREQUENCY THAN OTHER CARDIAC MUS THEY ARE THE PACEMAKER OF THE HEARTTHEREFORE, IT SETS THE HEARTRATE UNDER NORMAL Electrocardiography 3. Define ECG. THE GRAPHIC RECORDING OF THE ELECTRICAL CHANGES (DEPOLARIZATION FOLLOWED DURING THE CARDIAC CYCLE REPOLARIZATION) OCCURING DURING THE CARDIAC CYCLE. . Draw an ECG wave form representing one heartbeat. Label the P, QRS, and T waves; the P–R interval; the S–T segment, and the Q–T interval. R S T P T Q PR INTERVAL S QT INTERVAL 5. Why does heart rate increase during running? IN GREATER DEMAND WHEN OUR BODY IS UNDER THAT KIND OF STRAIN. THE HEART MUST BEAT FASTER AND HARDER IN ORDER TO DELIVER THE LARGER AMOUNT OF BLOOD TO MUSCLES BEING USED WHEN RUNNING 207 6. Describe what happens in the cardiac cycle in the following situations.
1. 2. 3. 4. 5. 6. mmediately before the P wave: during the P wave: HEART IS IN DIASTOLE DEPOLARIZATION OF ATRIA CONTRACTION OF ATRIA immediately after the P wave (P–R segment): during the QRS wave: DEPOLARIZATION OF VENTRICLES CONTRACTION OF VENTRICLES immediately after the QRS wave (S–T interval): during the T wave: REPOLARIZATION OF VENTRICLES 7. Define the following terms. 1. 2. 3. tachycardia: bradycardia: fibrillation: A HEART RATE OVER 100 BEATS/MIN A HEART RATE BELOW 60 BEATS/MIN RAPID, UNCOORDINATED HEART CONTRACTIONS THAT MAKES HEART USELESS AS A VENTRICULAR FIBRILLATION . Which would be more serious, atrial or ventricular fibrillation? Why? BECAUSE WHEN YOUR IN V-FIB YOUR PRETTY MUCH DEAD UNLESS THEY CAN SHOCK YOUR H WITH ATRIAL FIBRILLATION, IT CAN BE TREATED WITH ANTI-RHYTHMIC DRUGS 9. Abnormalities of heart valves can be detected more accurately by auscultation than by electrocardiography. Why is this so? ABNORMAL HEART VALVES CAUSE EXTRA HEART SOUNDS (S3 AND S4) THAT CAN BE HEARD WITH A AN ECG JUST MEASURES ELECTRICAL ACTIVITY IN THE HEART, IT REALLY DOESNT HAVE ANYTHING TO DO WITH HOW THE VALVES WORK. 208 Review Sheet 31