2. Circulatory System How does the heart work?

3. Heart beat Motor nerve Skeletal muscle The heart is myogenic  Generates its own electricity

4. Heart beat Sinus node  Plexus of nerves  Initiates contraction of cardiac muscle Atria  Heart’s “natural pacemaker” Sinus Node (SA Node)

5. Heart beat AV node  Receives impulse from SA Node  Delivers impulse to the His- Purkinje System Sinus Node (SA Node) Atrio- ventricular Node (AV Node)

6. Heart beat Bundle of His  Begins conduction to the ventricles Sinus Node (SA Node) Atrio- ventricular Node (AV Node) Bundle of His

7. Heart beat Purkinje System  Bundle branches  Purkinje fibers  Moves the impulse through the ventricles for contractions Sinus Node (SA Node) Atrio- ventricular Node (AV Node) Bundle of His Bundle Branches Purkinje Fibers

8. Heart beat SA node AV node both atria contract 0.1 second delay Both ventricles contract

9. Heart beat Pacemaker is controlled by the medulla oblongata Sympathetic nerves can speed heart rate up  Noradrenaline (neurotransmitter) Increases rate of cardiac muscle contraction Parasympathetic nerves can slow heart rate down  Acetylcholine (neurotransmitter) Decreases rate of cardiac muscle contraction Adrenaline (hormone) may also increase heart beat

10. Heart sounds (lub-dub) 0.1 sec delay results in 2 sounds Results from closing of valves  “lub” Recoil of blood against closed AV valves  “dub” Recoil of blood against semilunar valves Heart murmur  defect in valves causes hissing sound when stream of blood squirts backward through valve

11. Cardiac cycle 1 complete cycle of pumping  Heart contracts & pumps  Heart relaxes & fills  Contraction phase Systole Ventricles pump blood out  Relaxation phase Diastole Atria/ventricles fill with blood systolic ________ diastolic pump (peak pressure) _________________ fill (minimum pressure) 110 ____ 70

14. Measuring of blood pressure High Blood Pressure (hypertension)  if top number ( systolic pumping) > 150  if bottom number ( diastolic filling) > 90

15. Electrocardiogram (ECG or EKG) Measures electrical impulse through heart

16. Electrocardiogram – P wave Atrial depolarization  Caused by impulse from SA Node

17. Electrocardiogram – PQ segment Delay at AV Node

18. Electrocardiogram – PQ segment Conduction of impulse through Bundle Branches

19. Electrocardiogram – PQ segment Conduction of impulse through Purkinje Fibers

20. Electrocardiogram – QRS wave Ventricular depolarization  Ensures synchronized contraction of ventricles Contraction begins at apex

21. Electrocardiogram – ST segment Interval between ventricle depolarization and repolarization

22. Electrocardiogram – T wave Ventricle repolarization

23. Normal EKG activity

24. Putting it all together …

25. Any questions?