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42 Cards in this Set
- Front
- Back
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Non-contractile cardiac muscle |
Modified to initiate and distribute impulses |
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Sinoatrial node |
In right atrium Rate 100AP/min (modified to 75 by parasympathetic) |
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Atrioventricular node |
In right atrium Rate 50AP/min |
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Bundle of His |
Originates at AV node ONLY route for electrical activity to go from atria to ventricles |
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Purkinje fibres |
Terminal fibres (stimulate contraction of the ventricular myocardium) 30AP/mij |
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Interartial pathways |
Connects the 2 artials and makes them contract as a unit Via gap junctions |
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Internodal pathway |
Connects the SA and AV node (delay of .1 sec to get through AV node) |
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Artificial pacemakers |
Stim if SA or AV node damaged |
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Threshold of heart muscle cells |
-40mv |
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Pacemaker potential |
Slow inward leak of Na+ (channels open) Causes slow depolarization |
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AP depolarization |
Threshold meet Ca++ gates open Na gates close |
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AP repolarization |
Ca++ close at peak K+ opens (close below threshold) |
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Start of pacemaker cycle |
Na+ channels open at -50mv once K+ channels close NO RMP (it's always changing) |
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Phases of pacemaker activity |
1. Pacemaker potential 2. AP depolarization 3. AP repolarization 4. Na+ channels open at -50mV |
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AP in ventricular myocardium |
Cells=contractile Resting MP = -90mV |
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How signals spread in heart |
Via gap junctions |
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What type of gates allow ions through in the heart |
ALL voltages gated |
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Phases of ventricular myocardial APs |
1. Depolarization 2. Plateau 3. Repolarization |
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Depolarization |
Na gates open (fast) MP to +30 |
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Plateau |
Na channel close and inactivate Ca (SLOW) channels open |
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Repolarization |
Ca++ channels close K+ gates open |
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Absolute refractory period in ventricular myocardial |
Very Long Na+ channels inactivated until MP is close to -70 |
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Excitation contraction coupling in myocardial cells |
1. Ca++ voltage gated open Causing 2. Chemically gated Ca++ channels on SR Causing 3. Contraction |
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Contraction of myocardial cells |
Sliding filament mechanism Duration of AP = 250msec Duration of twitch = 300msec Contraction almost over when AP ends - no summation or tentanus - alternation of contration/reaction |
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3 components of cardiac cycle |
1. Electrical activity (ECG) 2. Mechanical activity 3. Blood flow through heart |
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How do currents move through the heart |
Via salty body fluids |
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ECG |
Potential differences measured on body surface using electric pairs Recording seen as waves |
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Electrode pair called |
A lead |
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ECG waves are |
Sum of electrical activity on ALL myocardial cells (NOT AP) Changes only 2 mV (not -40 to +30) |
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P wave (ECG waves) |
P wave = atrial depolarization followed by contraction |
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QRS wave |
- Ventricular depolarization followed by contraction - atrial repolarization followed by relaxation (masked by ventricular action) |
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T wave (ECG) |
Ventricular repolarization followed by relaxation |
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ECG P-Q interval |
Artia contracted Signal passing through AV node |
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S-T interval |
Ventrical contracted Atria relaxed |
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T-P interval |
Heart at rest |
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Tachycardia |
Resting heartrate above 100bmp |
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Bradycardia |
Resting heart rate under 60bpm |
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Heartblock |
When contractions through AVnode slowed - Increase P-Q interval - ventricles may not contract after each atrial contraction -ventricles follow AV node pass or purkinje rate ( bad!) |
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2 main mechanical events |
Systole = contraction, emptying Diastole = relaxation, filling Initiated by electrical activity |
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1 complete heartbeat is |
Diastole and systole of atria AND diastole and systole of venteicles |
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1 cardiac cycle takes how long |
0.8 seconds |
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When does ventricle contract |
0.1 second after atria for 3 msec. |
