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

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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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