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25 Cards in this Set
- Front
- Back
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What does cellular contraction depend on?
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Action potentials
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Cardiac contraction depends on
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Coordinated excitation.
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Coordinated excitation depends on
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A pacemaker and conduction systems.
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What is special about APs in the heart?
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They vary in shape in diff. regions of heart.
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What is the absolute refractory period?
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No response to any further stimulus.It is from fast upstroke to end of plateau(Na+ channels close for 100 ms)
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What is the relative refractory period?
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If stimulate cardiomyocyte hard enough-from end of plateau to after of repolarisation.
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What is the physiological purpose of refractory period?
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Ensures period of relaxation(filling)
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What is the cardiac pacemaker?
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SA node in the right atrium.
-specialised muscle cells -UNSTABLE resting mb potential. -diff. ionic channels conformation than in ventr. cardiomyocytes. |
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What is special about cardiac pacemaker cell?
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No electrical impulses needed to generate AP.(but input from brain via ANS can alter rate)
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What are the 3 ways to alter rate of firing of AP?
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-Increase slope
-lower threshold -move lower mb potential upwards. |
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WHat occurs first?
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Atrial contraction(just before ventricular contraction)
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What is the atrial kick?
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Extra kick of blood by atria into ventricles at end of ventricular diastole.
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What happens if ventricle contract before atrium contracts?
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No kick.
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What slows down conduction of AP?
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AV node
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Why does AV node slow conduction of AP?
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Ensures sufficient time for atrial contraction before ventricular contraction.(allows no more than 200 beats per min thru to ventricles)
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What is AF ?
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Jelly atrium which beats 400-600 time per min.(if >150 ,not good)
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WHat happens during ventricular depol. ?
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Cells depolarize and become activated.
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How does the wave spread?
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Quickly from BASE to APEX and from ENDOcardial to EPIcardial regions.
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What is the first thing to contract?
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Septum.It becomes rigid and acts as a solid foundation for contraction of ventricular walls.
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Heart consists of 2 layers of muscle and inside muscle contracts first,then outside.
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True
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What happens during ventr. repolarization?
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Activated cells return to resting state.
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How does the wave spread during ventr. repolarization?
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Less quickly from apex to base and from EPIcardial to ENDOcardial regions.(longer AP in septum)
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What does an ECG do?
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Record surface electrical voltages from voltage differences generated within heart.
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In an ECG,the magnitude of voltages depend on the mass of tissues involved(no. of cells)
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True-greater in ventricles than in atria.
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The direction of voltages is the sum of the depol. and repol. waves.
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True
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