Term
| What is the absolute refractory period? |
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Definition
| Inexcitable period where Na channels are open/inactive. ~250 ms, longer than skeletal muscle. |
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Term
| What are the areas of auto-rhythmic cells and their order of depolarization? |
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Definition
- Sinoatrial node - in right atria. Called the heart's pacemaker, sense sinus rhythm.
- Atrioventricular node - Spreads to AV node via internodal pathway. Immediately above tricuspid valve. Delays the signal slightly so atria can finish contraction.
- AV bundle/Bundle of His - in the septum, connects atria and ventricles
- Right and Left bundle branches - split in septum going towards apex. Depolarizes from left to right.
- Purkinje fibers - branches out into ventricular muscle, papillary muscle
- total time: 0.22 s
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Term
| What is resting membrane potential? |
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Definition
| The interior membrane is negatively charged relative to the outside due to potassium ion permeabilty. RMP varies from -40mV to -90mV |
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Term
| What is the flow of conduction in an SA nodal automatic cell? |
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Definition
| If (funny channel) opens, and Na/K influx. Depolarization from -45 to -20. At -20, Ca channels open at rapid depolarization occurs. At +10, Ik opens and potassium efflux, returning to -45. |
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Term
| What happens if you increase membrane permeability to potassium, And/Or decrease sodium permeability? Also happens when closing the funny channel. |
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Definition
| Depresses phase4 slope, RMP becomes more negative, heart rate slows. |
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Term
| What happens when membrane permeability to potassium increases due to Ik openings? |
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Definition
| Phase 3 and 4 severely depressed, hyperpolarization becomes more negative. |
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Term
| What happens when you decrease calcium permeability in phase 0? |
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Definition
| Slope of phase 0 curve shifts right without affecting phase 3 and 4. |
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Term
| How does the action potential of Purkinje fibers work? |
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Definition
| Phase 4 slow depolarization due to funny channel or potassium channels, then upstroke in phase 0 due to SA nodal signaling BEFORE reaching threshold potential. Without SA node, fires once reaching -45, too slow for life. |
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Term
| How does the action potential of ventricular muscle cells work? |
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Definition
NON-Automatic:
- Phase 4 (no-slope) is repolarization with K efflux.
- Phase 0 - depolarization with Na then Ca influx --> rapid upstroke.
- Phase 1 - Cl- influx, repolarization begins.
- Phase 2 - main contraction. Ca binds to troponin, CICR.
- Phase 3 - K efflux and hyperpolarization returning to phase 4 |
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Term
| What is the late sodium channel? |
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Definition
| In phase 2/contraction of a muscle cell, there is a late sodium channel that opens after Ca channels open. Opening prolongs repolarization. |
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Term
| When does abnormal sodium influx occur? |
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Definition
| Normally, Na can leave the cell due to a Na/K exchanger which requires ATP. In hypoxia, there is no ATP, so Na enters the cell from sodium and sodium/H exchangers. All the Na then exchanges for a massive amount of Ca, leading to arrhythmia. |
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Term
| What determines velocity of conduction/speed of transmission? |
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Definition
- Size of the fibers - small fibers are slower
- Presence of gap junctions - fewer are slower
- Level of Resting Membrane Potential (Potassium dependent) - Increase = more negative = increase velocity.
-Membrane responsiveness - sodium dependent, whether sodium channels reactivate or not. |
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Term
| How does sodium influence membrane responsiveness and conduction? |
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Definition
| The more negative the RMP, the more Na channels can open. More Na - greater rate of depolarization/phase 0/velocity. AKA more rapid upstroke. |
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Term
| How do the activation/inactivation gates work in sodium channels? |
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Definition
| Sodium gates start with Activation gate close and inactivation open. In phase 0, Activation opens and Na flows. As RMP becomes positive, inactivation closes for duration of refractory period. |
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Term
| What are the refractory periods? |
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Definition
Absolute refractory period - no sodium channels have been reactivated, will not respond. During phase 2.
Effective refractory period - Some Na channels reactivated, still not enough. Beginning of phase 3.
Relative refractory period - a slower depolarization can occur in the end of phase 3, looks like a bell curve. |
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Term
How do you prolong refractory periods? |
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Definition
- Open the late sodium channel at the end of phase 2. Cell stays positive longer but does NOT prolong the action potential
- Decrease K efflux in phase 3, cell stays positive longer, prolongs the AP.
- Delay reactivation of phase 0 sodium channel. AP is normal, ERP is longer as sodium channels cannot be stimulated.
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Term
| What happens if you influence the reactivation of phase 0/slow Na channels on ERP? |
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Definition
| Repolarization does not slow down, but ERP is prolonged. |
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Term
| What are the nervous ennervations of the heart? |
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Definition
| the PNS (vagus nerve) ennervates the SA and AV node only, while the sympathetic cardiac nerve/SNS ennervates these plus ventricular muscle. |
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Term
| How does the SNS affect the funny channel? |
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Definition
| Activation of the B1 receptor forms cAMP. cAMP binds directly to If, opening the channels and increasing the rate of phase 4 depolarization and therefore heart rate. |
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Term
| What is the intrinsic conduction system? |
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Definition
| Allows for proper sequence of activation and depolarization of atria and ventricles, no contraction. |
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Term
| What is a latent pacemaker? |
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Definition
| Everything besides the SA node, has the ability to become the pacemaker if the SA node is disabled. Conducts at a slower rate. |
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Term
| How long does it take the wave of depolarization to reach the AV node? |
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Definition
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Term
| How long does it take the wave of depolarization to make it through the AV node and bundle of His? |
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Definition
| 0.16 seconds. Point of slowest impulse. Main area of delay is the AV node. |
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Term
| Why does the impulse slow down in the AV node? |
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Definition
| Smaller fibers (large fibers conduct faster), less gap junctions, a more positive RMP (more negative = faster conduction), and slower/less sodium influx (More sodium = faster conduction) |
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Term
| At rest, what are the normal concentrations of ions inside and outside of the cell? |
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Definition
| K is higher inside of the cell, Na and Ca are higher outside of the cell. At rest, only permeable to potassium. |
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Term
| When a drug form of potassium is given, what happens to the cell? |
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Definition
| Increased levels of extracellular K result in K influx, RMP becomes more positive. Can lead to arrhythmia. |
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Term
| What are the phases of an SA nodal cell depolarization? |
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Definition
- Phase 4 - Potassium efflux. As it begins to depolarize and become more positive, K efflux slows, increase in Na influx. Funny channel opens - K/Na influx.
- Phase 0 - Reaches threshold, becomes permeable to calcium. Depolarizes into positive numbers.
- Phase 3 - K efflux and hyperpolarization returning to normal and phase 4. Funny channel reactivates. |
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Term
| What is cardiac excitability? |
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Definition
| How far below threshold potential phase 4 is. If RMP is more negative, decreased cardiac excitability. |
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