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68 Cards in this Set
- Front
- Back
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what type of muscle is cardiac muscle?
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striated
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how does cardiac muscle differ from skeletal muscle?
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has intercalated discs with desmosomes, gap junctions, has functional syncytium, huge mitochondria, extensive branching & variations in diameter that alter the arrangement of sarcomeres
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what are intercalated discs?
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discs that consist of desmosomes and gap junctions that enable the transmission of current across the heart
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what are desmosomes?
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physical anchors that prevent adjacent cells from separating during contraction
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what prevents adjacent cells from separating during contraction?
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desmosomes
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what are gap junctions?
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intercellular connections that enable the passage of ionic current from cell to cell
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what transmits current across the heart?
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intercalated discs
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what do desmosomes and gap junctions form?
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intercalated discs
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what are the intercellular connections that enable the passage of ionic current from cell to cell?
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gap junctions
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what is myocardium?
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heart muscle
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what do gap junctions do?
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couple the ionic basis of excitation contraction coupling between adjacent cells
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what is a functional syncytium?
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a single coordinated unit
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what term means the myocardium acts as a single coordinated unit?
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functional syncytium
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how do mitochondria differ in cardiac muscle compared to skeletal muscle?
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huge, occupy 25-35% of the volume of cardiac cells (2% in skeletal muscle)
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what is the volume of a cardiac cell filled with?
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25-35% mitochondria, most remaining volume with sarcomeres composed of the same filaments as those in skeletal muscles
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how does the arrangement of sarcomeres in cardiac muslce differ from skeletal muscles?
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the myofibrils of cardiac muscle cells vary in diameter and branch extensively, accommodating the larger mitochondria lying between them (less dramatic banding patttern than in skeletal m)
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the system for delivering calcium ions to the contractile elemens is BLANK elaborate in cardiac muscle than in skeletal muscle
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less
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what is different in the calcium ion delivery system in cardiac muscle vs skeletal muscle?
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T-tubules are wider and fewer, entering the cell only once per sarcomere at the Z-discs, the SR is simpler and lacks terminal cisternae, resulting in no triads
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what do T-tubules look like in cardiac muscle vs skeletal muscle?
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wider and fewer
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how do T-tubules enter cells in cardiac muscle?
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once per sarcomere at the Z-discs
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what does the cardiac muscle lack compared to skeletal muscle?
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lacks terminal cisternae (because SR is simpler) and triads
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what is different in the excitation-contraction coupling of cardiac muscle vs skeletal muscle?
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automaticity (autorhythmicity) as a means of stimulation vs nerves, syncytial vs motor unity, and 250msec vs 1-2msec of absolute refractory period
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what is the means of stimulation of cardiac muscle?
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automaticity (autorhythmicity)
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what is the means of stimulation of skeletal muscle?
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nerves
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what is the contraction unit of cardiac muscle?
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syncytial
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what is the contraction unit of skeletal muscle?
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as motor units
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what is the length of absolute refractory period of cardiac muscle?
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250msec
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what is the length of absolute refractory period of skeletal muscle?
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1-2msec
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what triggers cardiac muscle contractions?
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action potential
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what triggers skeletal muscle contractions?
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action potential
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What initiates a wave of depolarization in cardiac muscle?
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spontaneous depolarization
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how is depolarization transmitted?
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cell-to-cell via gap junctions
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how does the subsequent contractions of cardiac muscle occur?
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in a mechanical sequence that optimizes the ejection of blood when initiating impulse is generated from the appropriate pacing center and spreads over the myocardium along the normal pathway
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what is the pacing center?
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the spontaneous depolarizing cells
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how many myocardial cells have the spontaneous depolarizing feature?
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~1% of cardiac fibers, remaining fibers are contractile elements
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how does a fast cardiac AP begin?
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at phase 0 the initial upstrake of the AP occurs when depolarization opens voltage-gated fast Na+ channels
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what happens in a fast cardiac AP after voltage-gated fast Na+ channels open?
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extracellular Na+ briefly enters the cell triggering depolarization of the membrane potential until the Na channels are inactivated
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what causes a plateau in the fast cardiac AP?
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the inward flux of Ca++ (10-20% of total Ca++ necessary for triggering contraction) through slow Ca++ channels that were opened by the same voltage that opened the Na+ channels (they are called slow because their opening is delayed)
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what occurs in the ventricular myocardial cell after slow Ca++ channels open?
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the influx of Ca++ stimulates the release of Ca++ (the remaining required) from the SR
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what is the role of potasium in fast cardiac AP?
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fast K+ channels open wih NA+ flux, then close quickly while slow K+ channel opens and enables K+ flus that decreases membrane potential
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what occurs if Ca++ channels are open during a fast cardiac AP?
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Ca++ continues to enter and cells continue to contract
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when does tension development by myocardial cells occur?
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during the plateau and peaks after the plateau ends because the entry of extracellular Ca++ is the initiating event on coupling contractile activity to depolarization
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do cardiac muscles undergo summation?
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No!
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can tetanus occur with repeated stimulation in cardiac muscles?
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No!
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do cardiac muscle contractions get stronger?
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no, they are at the same tension (but the tension may be altered by autonomic nervous system input
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what can skeletal muscle do that cardiac muscle can't?
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form stronger contractions using summation and recruitment
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what events occur supsequent to depolarization?
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calcium exits the cell
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how does Ca++ enter myocardial cells?
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through voltage-gated dihydropyridine (DHP) receptor
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what does DHP stand for?
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dihydropyridine (a voltage gated receptor)
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how does the secondary increase in cytoplasmic Ca++ occur in myocardial cells?
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ryanodine (Ry) receptors
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what does Ry stand for?
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ryanodine receptor
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how are DHP and Ry receptors coupled in skeletal muscles?
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mechanically
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how are DHP and Ry receptors coupled in cardiac muscles?
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calcium-induced calcium release
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what is calcium induced calcium release?
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when the extracellular Ca++ enering through DHP channeles triggers the opening of the Ry channel (in cardiac muscles)
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calcium-induced calcium release occurs where?
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between the DHP and Ry receptors coupled in cardiac muscle
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what is a Ca++ signal created from?
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summed Ca++ sparks (release events) that establish an intracellular Ca++ concentration sufficient to bind troponin and initiate the interaction beteen myosin and actin that contract muscles
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what do Ca++ sparks do?
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create a Ca++ signal that establishes an intracellular Ca++ concentration sufficient to bind troponin and initiate the interaction beteen myosin and actin that contract muscles
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what is necessary to initiate interactions between myosin and actin?
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a Ca++ signal that establishes an intracellular Ca++ concentration that binds troponin
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what do myosin and actin do?
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shorten the muscle similar to skeletal muscle
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when does muscle relaxation occur?
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when the cytosolic Ca++ concentration becomes insufficient for sustained interactions with troponin
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what happens when cytosolic Ca++ concentration becomes insufficient for sustains interactions with troponin?
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relaxation occurs
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how does fre Ca++ concentration decrease?
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Ca++ ATPase & cell membrane Na+/K+ ATPase
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what does Ca++ ATPase do?
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pumps Ca++ back into the SR
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what does SR stand for?
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sarcoplasmic reticulem
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what does cell membrane Na+/K+ ATPase do?
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pumps Na+ out and K+ in that ultimately enables Ca++ (2) exchange for Na+ (3)
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becaues cardiac muscle contains a lot of mitochondria, it is intolerant of what?
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oxygen debt
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because cardiac muscle is intolerant of oxygen debt, what is the rule of metabolism?
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aerobic
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because cardiac muscle relies on aerobic metabolism, it can do what?
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oxidize a wide array of energy molecules depending on what is available
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