Term
| How many nuclei does a cardiac cell contain? |
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Definition
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Term
| T/F Cardiac cells contain T-tubules and sarcoplasmic reticulum. |
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Definition
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Term
| What is the purpose of intercalated discs? |
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Definition
| Intercalated discs are mechanical connections which keep the cardiac cells from pulling apart during contraction. Composed of fascia adherens and desmosomes. Also have electrical connections called gap junctions that allow for the propagation of action potential throughout the heart. |
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Term
| What makes of the sarcomere. |
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Definition
| Myofilaments of actin and myosin. |
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Term
| Draw and label the cardiac action potential cycle. |
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Definition
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Term
| What happens during phase 4 of cardiac action potential? |
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Definition
It is the resting potential.
-Sodium and calcium channels are closed
-potassium channels (inward rectifying) are open
-extracellular concentration of Na is greater than intracellular
-extracellular concentration of K is less than intracellular |
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Term
| What takes place during phase 0 of cardiac action potential? |
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Definition
-fast sodium channels open when the membrane rapidly depolarizes
-sodium channels only open for a brief period of time
-sodium channels close to inactive state
-sodium channels return to closed resting state when membrane repolarizes |
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Term
| What takes place during phase 1 of cardiac action potential? |
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Definition
Partial repolarization due to:
-efflux of K through transient outward channels
-inactivation of sodium channels |
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Term
| What takes place during phase 2 of cardiac action potential? |
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Definition
-L-type calcium channels open and remain open for relatively long time
-calcium influx more gradual than sodium
-these calcium ions trigger internal calcium release from SR
-K+ exits through delayed rectifier channels
-plateau caused by balance between influx of calcium and efflux of K+ |
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Term
| What takes place during phase 3 of cardiac action potential? |
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Definition
-K+ exits through delayed rectifier channels
-K+ efflux is greater than Ca2+ influx
-Eventually Ca2+ influx stops and soley K+ efflux
-membrane is depolarized by to resting potential |
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Term
| Which is longer the refractory period of cardiac or skeletal muscle cells? |
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Definition
| Cardiac muscle cells--allows time for ventricles to empty and refill. |
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Term
| Why can't an action potential be generated during the refractory period? |
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Definition
| B/c fast sodium channels are inactive. |
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Term
| What is the difference between the effective and relative refractory period? |
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Definition
| During the effective refractive period an action potential cannot be generated, during the relative refractory period an action potential can be generated with a large enough stimulus-but it is slow and weak. |
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Term
| What is the role of extracellular calcium in the contraction of cardiac muscles? |
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Definition
| Extracellular calcium is not sufficient to induce contraction of cardiac muscles however it signals to release intracellular calcium from the SR which then allows for contraction |
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Term
| How does calcium enter cardiac cells and during which phase? |
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Definition
| Calcium enters cardiac muscle cells via L type channels in the T-tubules and sarcolema during phase 2 of action potential. |
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Term
| Which opens first T-type Calcium channels or L-type calcium channels? |
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Definition
| T-type calcium channels open first during zero phase. |
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Term
| Which calcium channels must be activated for contraction to occur? |
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Definition
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Term
| Once calcium enters through L-type channels what does it activate? |
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Definition
| Ryanodine receptor 2 (RyR2) which are calcium gated--calcium causes confirmational change allowing the release of calcium from the SR |
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Term
| How does calcium release result in contraction of cardiac muscle? |
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Definition
| Calcium binds to troponin, cahnging the conformation of troponin/tropomyosin and allowing myosin to bind to actin. |
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Term
| What is the model for cardiac muscle contraction? |
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Definition
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Term
| During what phase do cardiac muscle cells have the greatest force from contraction? |
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Definition
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Term
| During what stage does relaxation take place? |
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Definition
| During the end of phase 2 beginning of phase 3. |
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Term
| What events cause relaxation? |
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Definition
| During the end of phase 2 and the beginning of phase 3 SERCA pumps most calcium back into the SR. The remaining calcium is removed by sodium-calcium exchanger and calcium pump. |
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Term
| How is calcium uptake into the SR regulated? |
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Definition
| Phsopholamaban regulated SR calcium reuptake. When phospholamban is phosphorylated it makes SERCA more active--cytoplasmic calcium levels go down and cardiac muscle cells relax. |
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Term
| How does the amount of calcium in the SR effect contraction strength? |
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Definition
| The more calcium that is released the stronger the contraction. |
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Term
| How is the force of contraction regulated? |
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Definition
All cardiac muscle cells contract, so cannot increase the number of cells to increase contraction strength. Instead calcium levels are regulated by modulating:
-amount of calcium into the cell
-calcium release by SR
-SERCA levels
-calcium efflux |
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Term
| What is the effect of stimulating the sympathetic nervous system on cardiac muscle cells? What is the mechanism for this? |
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Definition
Increases contraction and relaxation.
Mechanism:
-Stimulation of sympathetic nervous system leads to the release of catecholamines
-Catecholamines bind to beta adrenergic receptors
-B/Adrednergic receptors activate PKA
-leads to phosphorylation of L-type ca channels
-More calcium enters cell
- Increase in release of ca from SR
-Increase in calcium leads to increase in contraction strength
-Increase in PKA leads to phosphorylation of phospholamban which increases SERCA reuptake of ca to SR leading to an increase in relaxation. |
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Term
| What is the effect of beta adrenergic receptor blockers? |
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Definition
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Term
| What is the effect of stimulation of the parasympathetic nervous system on heart rate? What is the mechanism for this? |
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Definition
Lowers heart rate.
Mechanism:
-Acetylcholine released from nerve that binds to muscarinic receptors
-Acetylcholine inhibits kinases by preventing activation
-this slows the contraction rate by reducing intracellular calcium concentration |
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Term
| Which cells are more sensitive to cholinergic stimulation? |
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Definition
| Atrial cells are more sensitive to cholinergic stimulation than ventricular cells |
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Term
What is one way to treat congestive heart failure involving sodium potassium ATPase?
What is the mechanism for this? |
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Definition
With cardiac glycosides such as digoxin and ouabain.
-Inhibit ATPase
-Less Na gets pumped
-Increase in intracellular Na inhibits sodium-calcium exchange
-Leads to increased intracellular calcium
-Leads to greater contractions |
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Term
| What is the Frank-Starling Law of the heart? |
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Definition
| Stretching sarcomere increases the force of contraction |
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Term
| Why does the heart have greater passive resistance than skeletal muscle? |
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Definition
Titin
More extracellular matrix and thus more connective tissue |
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Term
| What are some factors that might allow cardiac muscle to increase its force of contraction with stretching? |
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Definition
-cardiac muscle has greater passive resistance than skeletal muscle
-actin and myosin filaments closer together during stretch
-increasing sarcomere length increases sensitvity of troponin c to calcium, which increases rate of cross bridge attachment and detachment (stretch takes less calcium to generate same force) |
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Term
| What is the decrease in contraction force due to at high degrees of stretch? |
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Definition
| Decrease is due to disruption of myocardial fibers--cardiac muscles stretch too far they break |
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