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17 Cards in this Set
- Front
- Back
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How many bpm is normal heart beat? |
60-80 bpm |
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What happens when heart rate is <40? |
Patient collapses, cardiac arrest occurs |
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Arrythmia |
- abnormal rate, rhythm, origin or conduction of impulses within the heart; caused by pacemaker elsewhere in heart other than SA or AV node |
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SA Node |
- sinoatrial node - initiates heartbeat, sending electrical impulses - "natural pacemaker" |
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AV node |
- atrioventricular node - electrical impulse from SA node spreads through the atria to the AV node -> impulses from AV node travel down to specialised fibres, His-Purkinje system to all parts of the ventricles |
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Importance of SA and AV nodes |
They both must be followed for heart to pump properly |
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Pacemaker cells (classification) |
- Round, oval in shape, very small - Found in SA and AV nodes - Reduced no. of myofibrils |
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Conducting cells |
- large cylindrical cells - reduced myofibrils - found in Bindle of His, bundle branches, and Purkinje fibres |
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Contractile cells |
- abundant myofibrils - extensive T-tubule system - predominant cell type in atria and ventricles |
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Nernst equation |
- Predicts membrane potential, assuming membrane permeability to a single ion |
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Goldman's equation |
Predicts membrane potential, assuming membrane permeability to more than one single ion |
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Ohm's law |
Conductance (g) is the inverse of resistance, thus a measure of the membrane's permeability to one or more ions. |
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Equilibrium potentials for Na, Ca, K, Cl |
ENa +60 ECa = +130 EK = -93 ECl = -80 |
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Fast response AP - phases |
0 - Upstroke and overshoot 1 - Rapid decrease of Na conductance due to time and voltage-dependent closing of channels; activation then inactivation of brief outward K channels 2 - L-type (long lasting activation) Ca channel; plateau phase; rapid at first, then turns off; heart doesn't function if Ca doesn't pass through 3 - Final repolarisation; Ions move against their currents 4 - Return to resting membrane potential; eventually effect of AP stops, AP is normalised |
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Slow response AP - phases |
0 - upstroke; slow increase of L-type Ca conductance, not Na 3 - repolarisation; slow decrease in Ca conductance, increase in K conductance 4 - maximum diastolic potential; lower resting K conductance, higher resting Na conductance; diastolic depolarisation - reduction in K conductance and/or steady inward current carried mainly by Na. Late in Phase 4, Ca conductance increases |
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Autonomic regulation of electrical activity (sympathetic) |
- Increased automaticity in pacemaker cells - Increased contractibility of atrial and ventricular cells - Alters AP configuration |
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Autonomic regulation of electrical activity (parasympathetic) |
- Decreased rate of SA and AV nodes - Decreased conduction velocity in AV nodes - Antagonises sympathetic stimulation in all areas of the heart |
