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15 Cards in this Set
- Front
- Back
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Adherens junction |
cytoplasmic face is linked to the actin cytoskeleton; appears as bands encircling the cell or as spots of attachement to extracellular matrix |
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Desmosome |
attach two adjacent cells formed from protein plaques in the cell membranes linked by filaments; keeps cell from being pulled apart |
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tight junctions |
specialized connection such that the spare usually lying between the two adjacent cells is absent; mainly in epithelial cells |
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P wave |
representing atrial depolarization (80ms) |
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PR interval |
from beginning of P-wave to beginning of QRS complex Reflecting the time from the SA node through the AV node and entering ventricles; good estimate of AV node function (120-200ms) |
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QRS complex |
rapid depolarization of right and left ventricles (80-120ms) |
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ST segment |
represents the period when the ventricles are depolarized (80-120ms) |
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T wave |
represents the repolarization of ventricles; the interval from the beginning of the QRS complex to the apex of the T-wave is refereed to as the relative refractory period (160ms) |
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U wave |
not always seen; small, representing repolarization of papillary muscles or Purkinje fibers Most seen in hypokalemia, hypercalcemia,... |
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Effect of sympathetic nerve on threshold potential in fast response cells (cardiomyocytes) |
- if a stimulus is not strong enough to depolarize the membrane to threshold, AP doesn't occur - the threshold potential (TP) of an excitable cell is NOT a fixed potential valve, but rather subject to influence by various factors (ex sympathetic n) |
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Comparison of AP/contraction between skeletal muscle and cardiac muscle |
Refractory period: after AP, during which another AP cannot be initiated - effective or absolute refractory period: ventricles absolute refractory period is ~200-250ms (till plateu); atrium is ~100ms, there s no response to stimuli - relative refractory period: 50ms, strong stimulus required for premature beats formation. Because the cell is stimulated from a voltage less negative than resting potential; its upstroke is less steep and lower amplitude and its conduction velocity slower than normal |
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Hodgkin-Huxley Model of Sodium channel gating and ARP (absolute refractory period) |
1. At resting membrane membrane potential the channel is closed but available for opening if challenged by a chemical or voltage stimulus 2. Activated open state the channel is open and permits the passage of ionic current 3. Inactivated state-channels closed and unavailable for activation. Cell refractory (as long as H-gates are closed- these gates are polypeptide that form one part of the transmembrane protein channel, and they undergo conformational changes in response to changes in voltage) |
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Absolute Refractory Period |
- begins when Na+ channels are inactivated during AP - lasts until Na+ channels begin to return to their resting state - during the ARP, a second action potential CANNOT be initiated regardless of the strength of the stimulus |
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Relative Refractory Period |
- immediately follows the ARP - second action potential can be triggered is a suprathreshold stimulus is applied - in this period some of Na+ channels have returned to their resting state and are available for activation |
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Significance of refractory period |
- protects the heart from too rapid re-excitation, which could impair its function as pump - protects the rhythmic excitation-relaxation recycling of the heart which would interfere with the rhythmic alternation of contraction and relaxation
o the refractory period of the excited myocardial cells is normally longer than time taken for spread of excitation over atria or ventricles o a wave of excitation originating from SA node can cover the heart only once at most, then dies out, because it encounter refractory tissue everywhere |
