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13 Cards in this Set
- Front
- Back
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Name the two types of cardiac muscle cell |
Contractile cell Autorhythmic cell |
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What is the resting potential of cardiac cells? |
-90mV |
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How is resting potential maintained? |
High concentration of K+ in the cell causes K+ to diffuse out, redistributing the charge across the membrane. The intracellular voltage then becomes more negative until a balance is reached between the two opposing forces. |
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Give the stages of a cardiac action potential |
-Phase 0: Depolarisation from threshold - fast sodium channels open at -60mV. Na+ floods into myocytes. -Phase 1: Spike - Na+ channels close, but K+ continues to move out causing a brief drop in membrane potential. Closing of K+ channels and opening of L type Ca2+ channels depolarise the membrane. - Phase 2: Plateau - Most K+ channels remain closed and most Ca2+ channels remain open. Membrane stays depolarised. - Phase 3: Repolarisation - Slow activating K+ channels open. K+ leaves and membrane repolarises |
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What effect does an increase in Ca2+ have on actin-myosin interactions? |
Increases cross bridge formation by increasing Ca2+ binding to troponin C |
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Give the names of the two refractory periods |
Absolute refractory period Relative refractory period |
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Describe the absolute refractory period |
Contraction lasts about 200-250ms -50mV to full repolarization - Prevents sustained contraction (tetanus) in mycardium |
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Describe the relative refractory period |
Not all fast Na+ channels are reset Larger than normal excitatory stimulus needed |
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Give the hierarchy of pacemaker cells |
SA node - dominant pacemaker Other atrial sites AV node Bundle of His Purkinje cells |
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Give the stages of contraction with regards to the wave of excitation |
-SA node activity begins -Stimulus spreads over atrial surface -Delay at AV node. Atrial contraction begins. - Travels along intraventricular septum in bundle of his -Impulse distributed by purkinje fibres, stimulating ventricular contraction
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What does the QRS complex represent on an ECG? |
Ventricular contraction |
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What does the ST segment represent on an ECG? |
Plateau after ventricular contraction |
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What is the T wave? |
Repolarization |
