Pages 363-370
Cardiac muscle cells contract: Spontaneously Independently
Two systems regulate heart rhythm: Intrinsic Conduction System
Uses the specialized cardiac muscle cells (nodal tissue)
75 beats per minute Autonomic nervous system
Speed up or slow down
Sinoatrial (SA) node Atrioventricular (AV) node Atrioventricular (AV) bundle (bundle of
His) Discovered by Wilhelm His in 1893
Bundle branches Purkinje fibers
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Superiorvena cava
Sinoatrial (SA)node (pacemaker)
Atrioventricular(AV) node
Right atrium
Bundle branches
Purkinje fibers
Left atrium
Atrioventricular(AV) bundle(bundle of His)
Purkinje fibers
Interventricularseptum
Sinoatrial Node = the heart’s natural pacemaker The “SA Node” Located in the right atrium Starts each heartbeat; sets the pace
From the SA node the impulse spreads: To the AV node – atria contract … Then the impulse travels to the:
AV bundle > Bundle branches > Purkinje fibers Ventricles contract toward atria, ejecting blood
http://highered.mheducation.com/sites/0072495855/student_view0/chapter22/animation__conducting_system_of_the_heart.html
Ischemia —lack of adequate oxygen supply to heart muscle results in fibrillation
Fibrillation—a rapid, uncoordinated
shuddering of the heart muscle Major cause of death from heart attacks Use of defibrillator can save life by restoring natural
rhythm using electrical current
Tachycardia —rapid heart rate over 100 bpm Prolonged can progress to fibrillation
Bradycardia —slow heart rate less than 60 bpm
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Cardiac cycle refers to one complete heartbeat
Refers to the sounds of the ventricles Systole contraction Diastole relaxation
beats about 75 times per minute length of beat is about 0.8 seconds
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Two distinct sounds “Lub” – closing of the AV valves-
ventricular systole (systolic blood pressure) “Dup” – closing of the semilunar valves
Ventricular diastole (diastolic blood pressure)
Faulty valves reduce efficiency of the heart Can lead to abnormal heart sounds (murmurs)
Sounds like a whooshing or swishing
1. Autonomic Nervous System Sympathetic nervous system Parasympathetic nervous system
2. Hormones and ions via Endocrine System
Epinephrine and thyroxine increase heart rate Imbalances of Ca⁺⁺ or K⁺ can depress, stop, or
increase heart rhythms
3. Physical factors Age : faster in young Gender : faster in females Exercise Body temperature
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