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57 Cards in this Set
- Front
- Back
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How many sarcomeres/myofibril?
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~50
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How many myofibrils/muscle fiber?
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~50-100
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What is the resting membrane potential of cardiac muscle?
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-85 to -95 millivolts
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What is the voltage of a cardiac action potential?
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105 mV
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What is the duration of a cardiac action potential?
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~409 to 420 msec
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What happens in phase 0 of the ventricular muscle action potential?
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Nav1.5 channels open, then L-type Ca++ channels open
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At what voltage do Nav1.5 channels open?
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-60 mV
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At what voltage do L-type Ca++ channels open?
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-40 mV
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What happens in phase 1 of the ventricular muscle action potential?
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Kv4.3 channels carrying Ito open
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What happens in phase 2 of the ventricular muscle action potential?
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L-type Ca++ channels remain open longer due to slow voltage dependent inactivation
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What happens in phase 3 of ventricular muscle action potential?
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KvLQT (carrying Iks) and Herg (carrying Ikr) open
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What happens in phase 4 of the ventricular muscle action potential?
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Kir2.1 channels carrying the Ik1 current (establishes the resting membrane potential) fully open
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What is Ito?
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Transient outward current, carried by Kv4.3
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What is Iks?
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Slow delayed rectifier current, carried by KvLQT
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What is Ikr?
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Rapid delayed rectifier current, carried by Herg
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What is Iki?
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Inward rectifier current, carried by Kir2.1
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Which is the only ion channel open at -80 mV?
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Kir2.1
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What is the ratio of Na/Ca ions exchanged by the Na/Ca exchanger?
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3Na+ for 1 Ca++
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What does the NCX do in the forward mode?
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Na+ into the cell, Ca++ out; inward current, net positive charge, depolarizing current
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What does the NCX do in the reverse mode?
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Na+ out of the cell, Ca++ out; outward current- net negative charge in cell
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What mode does the NCX go in during the action potential?
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Reverse then forward
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How does Calcium get out of the cytoplasm?
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75% back into the SR by SERCA
20% back through forward mode NCX 5% through Ca++ ATPase |
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How is stroke volume calculated?
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End diastolic volume-end systolic volume
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How is the ejection fraction calculated?
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stroke volume/end diastolic volume
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How is cardiac output calculated?
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HR*stroke volume
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What is systole?
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Period of heart contraction and blood ejection
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What is diastole?
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Period of heart relaxation, heart fills with blood, muscle reestablishing Na/K/Ca gradients
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How does systole begin?
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Closing of AV valves and isovolumic contraction
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What is isovolumic contraction?
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Ventricular tension increases, but not shortening?
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What is the result of increased ventricular pressure during systole?
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Aortic valve is pushed open, ejection phase
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What happens during diastole?
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Isovolumic relaxation, AV valves open, rapid and slow ventricular filling and atrial systole
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What is automaticity?
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Ability of cardiac tissue to initiate its own beat
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What is rhythmicity?
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Regularity of pacemaking activity in cardiac tissue
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What is the location of the sinus node?
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Right atria below and lateral to opening of superior vena cava
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Why does the sinus node act as a pacemaker?
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Because membrane leaks Na+ , via If (hyperpolarization activated), a sustained inward current (Ist) which is activated around -60mV and ICaT
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How long does it take for the AP from the SA node to reach the AV node?
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30 msec
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What is the delay of the AP in the AV node?
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90 msec
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What is the delay of the AP in the AV bundle?
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40 msec
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What is the purpose of the delay of the AP in the Av node?
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Allows the atria to contract and fill
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What is the Purkinje system?
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Fibers that lead from AV node thorough AV bundle into ventricles
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What is the transmission time between AV bundles and the last of ventricular fibers?
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60msec (QRS time)
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What is the time of arrival of the cardiac impulse to the AV node?
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30msec
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What is the time of arrival of the cardiac impulse to the AV bundle?
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120msec
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What is the time of arrival of the cardiac impulse to the ventricular septum?
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160 msec
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How does the parasympathetic system affect heart rate?
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Parasympathetic (vagal) nerves which release acetylecholine at their endings, innervate SA node and AV junctional fibers proximal to AV node; causes hyperpolarization because of increased K+ permeability in response to Ach-- causes decreased transmission of impulses maybe temporarily stopping heart rate
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How does the sympathetic system affect heart rate?
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Releases norepinephrine at sympathetic ending, causes increase sinus node discharge
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What is the dromotropic response?
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increased rate of conduction of impulse
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What is the inotropic response?
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Increased force of contraction in atria and ventricles
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What is the chronotropic response?
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Increased rate of contraction
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What is the lusitropic response?
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Increased rate of relaxation
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What are the two phases of ventricular repolarization?
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plateau and rapid
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What does the QT interval represent?
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ventricular systole, period of ventricular depolarization and repolarization
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What happens during the TR interval?
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Ventricles are relaxed and filling with blood
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What happens during the ST segment?
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Represents the plateau phase of repolarization
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What is the concentration of Na+ inside and outside of the cell?
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10 mM inside and 145 mM outside
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What is the concentration of Ca++ inside and outside of the cell?
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0.1mM inside and 1.5 outside
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What is the concentration of K+ inside and outside of the cell?
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150 mM inside and 4 mM outside
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