Term
| What types of muscle cells are found in the myocardium? |
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Definition
contractile cells
autorhythmic cells |
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Term
| What is the difference between contractile & autorhythmic cells? |
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Definition
contractile cells require an action potential for contraction
autorhythmic cells an spontaneously generate their own action potential |
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Term
| What are gap junctions, and what is their importance? |
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Definition
water-filled pores between adjacent myocardial cells
-allow ions to move freely from one cell to another (electrical activity can move from cell to cell) |
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Term
| Which node determines heart contraction and why? |
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Definition
| Sino-Atrial node because its autorhythmic ability is at a faster pace than the atrio-ventricular node |
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Term
| Which node is the gateway for interaction between the atria and ventricles? |
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Definition
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Term
| What is the role of the bundle of His and Purkinje fibers? |
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Definition
| help to quickly propagate electrical activity from the AV node to the rest of the ventricles |
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Term
| What is the role of the electrical system of the heart? |
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Definition
-maintain an appropriate heart rate
-coordinate contraction of atria & ventricles
-coordinate contraction of each chamber |
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Term
| What is the sequence of excitation of the electrical system of the heart? |
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Definition
1. Self excitation of SA node (AP generated)
2. AP propagate through atria (atrial contraction)
3. AV node activated, electrical activity transmitted to bundle of His & Purkinje fibers
4.Electrical activity propagated through ventricles (ventricular contraction) |
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Term
| Under normal conditions, what drives the self-depolarization of cells in the SA node? |
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Definition
Na+ leaks outside of the cell, K+ diffusion inside the cell is reduced, creating a gradual drift in membrane potential until the AP is generated
cycle then repeats |
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Term
| What action does the ANS have on the autorhythmic ability of SA node cells? |
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Definition
sympathetic fibers - reduce time required to reach threshold
parasympathetic fibers - increase the time required to reach threshold |
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Term
| How does the action potential of contractile cells differ from that of autorhythmic cells or skeletal muscle? What is the importance? |
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Definition
-has a stable RMP (no drift, unlike autorhythmic)
-has a long duration (skeletal is short)
-has a long refractory period (skeletal is short)
This means the muscle cells can't re-excite a frequently, prevents cramping in heart muscle |
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Term
| What are the phases of depolarization/repolarization of cardiac contractile cells? |
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Definition
1. RMP
2. Na+ influx, rapid depolarization
3. Some K+ outfow, short repolarization
4. Plateau phase - Ca2+ flows in
5. Repolarization as K+ flows out |
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Term
| Describe the steps of calcium-stimulated calcium release |
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Definition
1. Depolarization
2. Voltage-gated Ca++ channels open
3. Ca++ release triggers further release of Ca++ from sarcoplasmic reticulum
4. Increase in Ca++ triggers contraction
5. Ca++ pumped back into its compartment |
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Term
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Definition
| cells are overstimulated and stay in a contracted state |
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Term
| Why do all cells of heart muscle contract at once? |
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Definition
| gap junction = rapid distribution of electrical impulse |
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Term
| What effect does the sympathetic nervous system have on the heart? |
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Definition
-increases heart rate
-stimulate firing of SA node
-stimulate speed of AV node conduction
-increases release of Ca++ from sarcoplasm (increase contractile force)
-increases Ca++ transport speed (reduces contraction time) |
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Term
| What mediates the effect of the sympathetic system on heart rate? |
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Definition
| epinephrine/norepinephrine on B-andrenergic receptors in ALL cardiac cells |
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Term
| What effect does the parasympathetic nervous system have on the heart? |
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Definition
-decreases heart rate
-reduces firing of SA node
-decreases speed of AV node conduction |
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Term
| What mediates the effect of the parasympathetic system on heart rate? |
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Definition
binding acetylcholine on muscarinic receptors in autorhythmic cells
-increases K+ permeability
-hyperpolarization increases the time required to reach AP threshold |
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Term
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Definition
| means of measuring heart membrane potential during the cardiac cycle by measuring the electric current conducted through body fluid to the skin |
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Term
| What does the P wave represent? |
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Definition
| depolarization of the atria |
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Term
| What does the QRS wave represent? |
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Definition
| depolarization of the ventricles |
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Term
| What does the T wave represent? |
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Definition
| repolarization of the ventricles |
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Term
| What things are measured in an ECG? |
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Definition
heart rate (intervals between cycles)
contraction force (amplitude of waves)
rhythm (intervals between waves) |
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Term
| What does abnormally long P-Q interval indicate? |
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Definition
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Term
| What do ectopic beats indicate? |
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Definition
| an AP is being generated independently of the SA node |
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Term
| What is the term for a slower heart rate than normal? |
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Definition
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Term
| What is the term for a faster heart rate than normal? |
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Definition
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Term
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Definition
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