Term
| True or False: The heart is able to beat spontanenously without input from the nervous system. |
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Definition
| True. This is true because cardiac cells are able to produce the electrical signal spontaneously. |
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Term
| What are the 5 major properties of the heart that regulate coordinated spontaneous activity? |
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Definition
1. Automaticity 2. Rythmicity 3. Excitability 4. Conductivity 5. Contractility |
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Term
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Definition
| The ability of the heart to spontaneously generate the membrane action potential necessary for each heartbeat. |
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Term
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Definition
| Defined as the regular occurence of electrical events that generate the sequential beating of the heart. |
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Term
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Definition
| The ability of the heart to respond to external stimuli, such as electrical stimulations. |
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Term
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Definition
| The capacity of the cardiac cells to propagate action potentials along the entire lengh of each cell as well as in between cells. |
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Term
| Explain how cardiac muscles cells differ from skeletal muscles cells such that they can be referred to as a "syncytium". |
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Definition
| Cardiac cells differ from skeletal cells in that they do not operate as individual distinct entities, but instead branch and anastomose to form meshworks of fibers throughout the atrial and ventricular walls. |
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Term
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Definition
| The ability of the cardiac cells to contract in response to electrical stimuli. |
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Term
| Jepoardy style: This is a group of specialized cells located on the posterior wall of the right atrium, close to points of entry for the vena cava. |
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Definition
| What is the sinoartrial (SA) node? |
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Term
| Describe the spread of electrical activity after the origin in the SA node. |
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Definition
SA Node -> Atria -> AV Node -> Purkinje Fibers -> Ventricles |
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Term
| The action potential generated by the pacemaker cells is called a ______________ potential. |
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Definition
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Term
| What is the resting membrane potential of pacemaker cells? What implication does this have on automaticity? |
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Definition
| The resting membrane potential of cardiac cells is -50mV (versus -90mV in ventricular cells). This is the primary reason that pacemaker cells can fire spontaneously. |
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Term
| What causes the electrical signal in cardiac cells? |
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Definition
| Caused by the ionic gradients across the plasma membrane and selective opening and closing of ion channels, a group of transmembrane proteins, in response to changes in the membrane voltage. Na+, K+ and Ca2+ contribute to the cardiac electrical activity. |
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Term
| What is Phase 0 of the cardiac membrane potential? |
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Definition
| Rapid membrane depolarization. When the cardiac cell is depolarized above a threshold potential, Na+ channels open allowing Na+ to enter into the cell. |
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Term
| Defects in the structural region of the Na+ channel protein is responsible for what type of syndrome, a disease associated with abnormal repolarization and ventricular tachycardia? |
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Definition
| Congenital long QT syndrome |
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Term
| What is Phase 1 of the cardiac cycle? |
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Definition
| Notch, or partial repolarization. Due primarly to the inactivation of Na+ channels and to much less extent the activation of K+ channels. |
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Term
| What is Phase 2 of the cardiac cycle? |
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Definition
| Plateau phase of cardiac action potential. Inward depolarizing Ca2+ current primarily through Ca2+ channels maintains the cell depolarization during the plateau phase. Phase 2 is prominent in ventricular myocytes, where Ca2+ influx trigers muscle contraction. |
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Term
| What is Phase 3 of the cardiac cycle? |
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Definition
| Repolarization of cardiac cells. Phase 3 is primarly due to efflux of K+ through K+ channels, and to a much lesser degree inactivation of the Ca2+ current. |
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Term
| What is Phase 4 of the cardiac cycle? |
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Definition
| The resting membrane potential. Phase 4 results from K+ efflux through K+ channels. |
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Term
| Where are fast type action potentials found? |
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Definition
Atrial Muscle Atrial Internodal Tracts Purkinje Fibers Ventricular Muscle |
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Term
| What is characteristic of fast action potentials? |
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Definition
1. A stable resting potential of approximately 90 mV. 2. Action potential of approximately 120 mV. 3. Very rapid depolarization phase, due to rapid opening of voltage-gated Na+ channels and influx of Na+ ions through Na+ channels. |
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Term
| What is characteristic of slow action potentials? |
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Definition
1. Less negative resting potential of -50 to -60 mV. 2. Less magnitude of action potential. 3. Requirement of less depolarization to reach threshold. 4. Shorter action potential duration of 150 msec. |
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Term
| What is the primary role of the Na+-K+ ATPase pump? |
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Definition
| Used to maintain the normal asymetrical distribution of Na+ and K+ ions across the cell membrane. This helps also to develop the repolarized state of the membrane. |
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Term
| What during Phases 0, 1, 2, and part of 3 can cardiac cells not undergo depolarization? What is the implication of this? |
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Definition
| Because Na2+ channels are still inactivated. Tetanic contractions cannot be induced in cardiac muscle. |
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Term
| How is the action potential spread in cardiac muscle from cell to cell? |
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Definition
| Via gap junctions in intercalated discs. |
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Term
| What portions of the heart display pacemaker activity? |
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Definition
| SA node, AV node, and Purkinje Fibers |
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Term
| What mechanisms are established to form the pacemaker hierarchy? |
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Definition
1. Intrinsic Rate - normally the fastest pacemaker sets the heart rate and overrides all others. 2. Time required to reach phase 4 repolarization 3. Refractory period |
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Term
| After the SA node, which pacemaker cells are next in line to set the pace of the heart? |
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Definition
| Normally, the AV node is next inline after the SA node. When overall ventricular depolarization rate is too low, implantation of a pacemaker is necessary. |
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Term
| What are the interatrial and internodal pathways in the atria? |
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Definition
| These are responsible for propogating the signal from SA node to the atrial muscle and AV node respectively. |
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Term
| What is the only point of electrial communication between the atria and ventricles? |
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Definition
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Term
| What is the clinical significance of having a slower conduction through the AV node? |
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Definition
| The slow conduction delays activation of the ventricles which allows for complete emptying of the atria into the ventricles before contraction. |
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Term
| How can conduction velocity through the AV node be altered? |
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Definition
Sympathetic - Speeds up conduction velocity through the node Parasympathetic - Slows down the conduction velocity through the node |
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Term
| The action potential exits the AV node into the ___________, which bifurcates into the _________________________. |
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Definition
| bundle of His, left and right bundle branches. |
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Term
| What is the cause of ventricular arrhythmias? |
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Definition
| Since conduction through the Perkinje fibers is very rapid, spontaneous conduction can occur causing arrhythmias. |
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Term
| True or False: Impulse conduction occurs from Epicardium to Endocardium. |
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Definition
| False. Conduction occurs from Inside to Out, or Endocardium to Epicardium. |
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Term
Administration of norepinephrine will ___________ the activity of Ca2+ channels. This will result in an __________ in heart rate. |
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Definition
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Term
What is the affect on heart rate on each of these items: 1. Norepinephrine 2. β-Blockers 3. Acetylcholine 4. Atropine |
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Definition
1. Increase HR 2. Decrease HR 3. Decrease HR 4. Blocks parasympathetic activity and increases HR |
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Term
| True or False: Cholinergic effects on the atrial and ventricular muscle include decreased contractility. |
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Definition
| False. Cholinergic effects are little to none on atrial and ventricular myocytes. |
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Term
| Rate of spontaneous depolarization can also be affected by which two non-neuronal factors? |
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Definition
High Body Temperature (Fever) Elevated Plasma levels of thyroxin (Hyperthyroidism) |
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Term
| What is the affect of accumulated K ions extracellularly because of failure of Na+-K+ pumps in ischemic regions of the heart? |
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Definition
| Reduced resting potential, slower phase 0 depolarization, reduced AP amplitude, and shortened AP duration. |
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