Heart Part 2

Heart beat is controlled by Autonomic Nervous System * Cardiac center in medulla oblongata (in brain stem)

Cardio-acceleratory center | Cardio-inhibitory center | - Innervates SA and AV nodes, heart muscle and coronary arteries with sympathetic neurons | - Inhibits SA and AV nodes with parasympathetic fibers in vagus nerves |

Vasomotor center in Medulla Pressor area: increase blood pressure via vasoconstriction Depressor area: decreases blood pressure by inhibiting nerves causing vasoconstriction
Cardio-acceleratory center: activated when pressor area is stimulated
Cardio-inhibitory center: depresses heard activity

Basic Heart Rate is set by intrinsic conduction system can be modified by ANS according to body’s needs

Sympathetic Nervous system:
Accelerator increases Heart rate and increases force of contraction

Parasympathetic nervous system:
“the break” decreases heart rate
Basic Heart Rate is set by intrinsic conduction system can be modified by ANS according to body’s needs

Sympathetic Nervous system:
Accelerator increases Heart rate and increases force of contraction

Parasympathetic nervous system:
“the break” decreases heart rate

Heart rate under Parasympathetic stimulation | Heart rate under Sympathetic stimulation | * Decreased heart rate when Ach opens chemically gated K+ channels * Slows (decreases) the rate of spontaneous depolarization | * Increased heart rate when norepinephrine is released by sympathetic neurons opening ion channels * Increases rate of depolarization * Shortens period of repolarization |

Electrocardiograph (EKG or ECG) Record of electrical activity of the heart Composite of all action potentials generated at any given time (nodal and contractile) 12 leads + 9 electrodes (in a clinical setting)

3 distinguishable waves 1. P Wave = atria depolarization (after atria contraction) 2. QRS complex = ventricular depolarization (after ventricular contraction) 3. T wave = ventricular repolarization (during ventricular excitation)

P-Q interval marked from the beginning of the atrial excitation to the beginning of ventricular excitation * atrial depolarization + contraction * passage of depolarization to the rest of the conducting system

S-T segment action potential in plateau * depolarization of entire ventricle myocardium

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a) Normal sinus rhythm

b) Junctional rhythm * SA node non-functional * HR paced by AV node (40/60 BPM) * P waves absent c) Normal sinus rhythm

d) Junctional rhythm * SA node non-functional * HR paced by AV node (40/60 BPM) * P waves absent

c) Second degree heart block
- some P waves are NOT CONDUCTED through the AV node
- >P than QRS waves

d) Ventricular fibrillation - seen in acute heart attack and electrical shock c) Second degree heart block
- some P waves are NOT CONDUCTED through the AV node
- >P than QRS waves

d) Ventricular fibrillation - seen in acute heart attack and electrical shock

Steps seen in Electrocardiography 1. Atrial depolarization, initiated by SA node, causes the P wave 2. With atrial depolarization complete, the impulse is delayed at the AV node 3. Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs 4. Ventricular depolarization is complete 5. Ventricular repolarization begins at apex, causing the T wave. 6. Ventricular repolarization is complete

yellow = depolarization red= repolarization
Heart blocks Defective AV node
May result in: 1. Partial heart block - Only some impulses from SA node reach the ventricles 2. Total heart block - No impulses get through and the ventricles beat at their own intrinsic way (too slow)
Heart sounds
LUB-DUP sound = closing of heart valves

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