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Cardiac Conducting System
Cardiac muscle tissue contracts on its own
No neural nor hormonal control
Specialized cells: initiate and distribute depolarization
1. Sinoatrial node (SA node)
a. Near entrance of superior vena cava/posterior wall of
R. atrium
b. “pacemaker cells” establish heart rate
c. Connected to AV node via conducting pathways
d. Stimulus affects only ATRIA
i. Fibrous skeletal separates atria from ventricle
2. AV node:
a. Floor of right atrium
b. Near opening of coronary sinus
c. From AV to bundle of His(bundle branches) which run
along interventricular septum
d. Delay at AV node allows atria to complete contraction
before ventricular contraction begins
3. AV bundle(bundle of His)
a. Impulse reaches AV bundle- travels along septum,
splits between L & R bundle branches
b. Purkinje fibers – where the bundle of His diverge into
smaller branches
i. Cause ventricular contraction
ii. Wave action from apex(bottom) to base(top)
iii. Blood is pushed out aortic and pulmonary trunk
Monitors electrical activity of heart
1. P wave: small, atria contract after start of P wave –
depolarization of atria
2. QRS complex: ventricles depolarize – STRONG electrical
signal – ventricles contract AFTER peak at R
3. T wave – ventricles relax
4. Do not “see” atrial relaxation due to strong QRS
Problems detected:
Extension of P-R interval = damage to conducting pathways or
damage to AV node
Extension of Q-T interval = myocardial damage
HEART ATTACK – myocardial infarction
Infarct = nonfunctional area of myocardium
Enzymes that detect MI= LDH; SGOT; CPK(creatine
Systole – contraction
Diastole – relaxation
On patient with stethoscope
Patients upper area right of sternum – hear pulmonary
semilunar valve
Lower right of sternum – hear right atrioventricular valve
Upper right of sternum – hear aortic semilunar valve
Lower right of sternum – left atrial ventricular valve – bicuspid