Term
| What is the pathway of electrical conduction in the heart? |
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Definition
1. SA node
2. Atrial muscle
3. AV node
4. AV bundle
5. Purkinje fibers
6. Ventricular muscle |
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Term
| What is the resting membrane potential of SA node cells? |
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Definition
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Term
| What is 'pacemaker potential'? |
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Definition
| The ability of SA node cells to depolarize independently of the brain |
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Term
| How do cells of the SA node depolarize/repolarize? |
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Definition
1. Na+ leaks into the cells via 'funny channels', causing mmb pot to drift from -60 to -40
2. L-type Ca2+ channels open, allowing influx of Ca to create a more positive charge.
3. K+ channels open, allowing K+ OUT of the cell to repolarize. |
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Term
| What is the role of the AV node/bundle? |
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Definition
1. Controls fibrillation entry to the ventricles via the fibrous body
2. Back-up pacemacker if the SA node fails (has fewer funny channels but works the same way)
3. Delay the AP conduction to increase filling of the ventricles (has fewer gap junctions). |
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Term
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Definition
HCN
hyperpolarizing activated cyclic nucleotide gated channels |
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Term
True or False
Ventricles contract as a single unit |
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Definition
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Term
| What is the resting membrane potential of cardiac muscle cells? |
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Definition
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Term
| How do ventricular muscle cells contract/conduct an AP? |
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Definition
1. Na+ channels open, rapid influx. Mmb -80 -> +40
2. Channels close, Na+ quickly removed
3. Plateau period, Ca+ enters while Na is removed
5. Ryanodine receptors detect Ca+, release more Ca+.
6. Muscle contracts
7. Ca+ & K+ are removed from the cell, repolarizing the mmb. |
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Term
| What happens during the 'plateau period' of ventricular muscle activation? |
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Definition
Plateau is caused by Na+/Ca2+ exhanger.
-binds Na+ inside the cell, Ca2+ on outside of cell & exchanges them
-L type channels also open causing further Ca+ influx
Result: Ca+ comes in at the same rate as Na+ moves out, balancing the charge across the membrane |
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Term
| What is ventricular tachycardia? |
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Definition
4 or more ventricular premature complexes in a row
-atria aren't functioning properly, ventricles can't fill with blood properly |
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Term
| How does lidocaine work to treat ventricular tachycardia? What are the cons? |
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Definition
Na+ channel blocker to stabilize changes in mmb potential
-non specific, so will block Na+ channels elsewhere, not just in the heart |
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Term
| Why is decreasing contractility of heart muscle via Na+ blockers to treat tachycardia, not necessarily a good idea? |
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Definition
| Na+ blockers are non-specific, will target all sodium channels not just the ones in defective cardiac cells |
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Term
| How does ivabradine work? Why is it preferable to lidocaine? |
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Definition
Targets funny channels, binding to open channels to hold them in an "inactive" state for a longer period of time, preventing Na+ from entering the cells.
-reduces the risk of bradycardia
- only targets channels that are malfunctioning |
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Term
| What is sick sinus syndrome, and how do you treat it? |
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Definition
SA node fires inappropriately
-problem manifests itself differently in each case, so not easily treated with drugs
-best to use a pacemaker, which stimulates atrial muscle right next to the SA node, mimicking its action |
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