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27 Cards in this Set
- Front
- Back
The electrocardiogram (EKG or ECG) is
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a means of recording electrical activity of the heart from externally-applied electrodes.
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For ECG, the P-wave
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corresponds to depolarization of the atria
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For ECG, the ORS complex
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is the result of ventricular depolarization.
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For ECG, the T-wave
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is the result of ventricular repolarization
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The EKG can be used to detect
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abnormalities in electrical events
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The EKG cannot be used to detect
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abnormalities in mechanical activity unless it also causes electrical disturbance.
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Atrial depolarization occurs ________ ventricular depolarization.
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before and separated from.
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The role of the AV node is
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to delay transmission of AP from atria to ventricle.
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The pacemaker of the heart is
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SA node.
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SA node is the pacemaker of the heart because
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it drives AV node to threshold.
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A wave of depolarization coming towards a positive electrode will cause ________ on ECG.
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positive deflection
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A wave of depolarization going away from a positive electrode will cause ________ on ECG.
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negative deflection
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The ultimate stimulus for cardiac muscle contractions is
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the increase in cytosolic Ca2+ concentration
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For excitation-contraction coupling in the heart, AP induced on the plasma membrane are carried into the cell by
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T-tubules
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For excitation-contraction coupling in the heart, during the plateau phase of the cardiac AP
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calcium flows into the cells.
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For excitation-contraction coupling in the heart, extracellular calcium triggers
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release of Ca2+ from SR.
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For excitation-contraction coupling in the heart, extracellular calcium activates
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contraction process
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For excitation-contraction coupling in the heart, the increase in cytosolic Ca2+ concentration that initiates contraction is the result of
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Ca2+ being released from the SR and entering the cell from outside.
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For excitation-contraction coupling in the heart, during repolarization Ca2+ is removed from cytosol by
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1. Primary active Ca2++-ATPase pump into SR, and 2. Primary active Ca2+-ATPase pump and Ca2+/Na+ exchanger out of the cell.
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The amount of free Ca2+ that is available to trigger the process of cross-bridge formation is a direct determinant of
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the strength of cardiac contraction.
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Mechanisms for controlling the strength of contraction occur through
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factors that increase or decrease the amount of free Ca2+.
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The steps of excitation-contraction coupling in the heart are
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1. Depolarization of plasma membrane, 2. Opening of plasma membrane L-type Ca2+ channels in T-tubules, 3. Flow of Ca2+ into cytosol, 4. Ca2+ binds to Ca2+ (ryanodine) receptors on surface of SR and opens Ca2+ channels, 5. Cytosolic Ca2+ concentration increases, 6. Cross bridge cycling and contraction.
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Examples of control mechanisms to change free calcium concentrations are
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autonomic nervous system and drugs.
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The refractory period of cardiac muscle lasts
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almost as long as mechanical contraction
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During the refractory period of cardiac muscle, _______ can not be elicited.
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further muscle contractions
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The refractory period of cardiac muscle is due to
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long plateau phase seen in cardiac AP.
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Unlike skeletal muscle, is impossible to produce _______ in cardiac muscle.
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Tetanic contractions.
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