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Myocardial Cells: Location, primary function, primary property
- Location: Myocardium
- Primary Function: Contraction relaxation
- Primary Property: Contractility
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Pacemaker Cells: Location, primary function, primary property
- Location: Electrical conduction system
- Primary Function: Generation and conduction of electrical
- impulsesPrimary Property: Automaticity, Conductivity
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Current
the flow of electrical charge from one point to another
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Voltage
measurement of potential energy (volts or milivolts)
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Electrolytes
elements or compounds that break into charged particles when melted or dissolved into water or another solvent (Na, K, Ca, Cl)
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Action Potention
transient depolarization and repolarization of cells that is triggered by external mechanisms
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Resting membrane potential
electrical charge across a cell membrane (Ca, Na, K)
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Threshold membrane potential
at which the cell will depolarize and become more positive
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slow response
- because fewer channels and intercalated disks
- SA and AV nodes (Slow calcium and sodium channels) Spontaneous action potentials
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fast response
- Atria, ventricles and Purkinje system (Voltage sensitive sodium channels)
- sensitive to sodium
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Polarization
- resting membrane potential (-90mV)
- resting state without electrical changes
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what leaks out during depolerization to maintain threshold?
K+
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Depolarization
- resting to positive state
- Na+ enters the cell
- electrical stimulus proceeds from endocardium to epicardium
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P wave?
Atrial Depolarization
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QRS complex?
ventricular depolarization
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repolarization
- Na+ stops flowing into cell
- K+ leaks out
- Returns to negative state inside cell
- relaxation of contractile proteins
- Electrical stimulus proceeds from epicardium to endocardium
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Phase 0?
Rapid Depolarization
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Phase 1?
Early Repolarization
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Phase 2?
Repolarization (plateau phase)
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Phase 3?
Rapid Repolarization
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Phase 4
Resting membrane potential
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What happens as cell is rapidly depolarizing?
cells recieve impulse, Na+ comes in, Ca2+ comes in slowly, and K+ diffuses out slowly
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What happens as cell is in early repolarization?
Na+ Channels partially closed (slowly come in), Cl- enters and K+ leaves
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What happens as cell is repolarizing?
- Ca2+ comes in slowly, K+ leaces
- ST segment (absolute refractory period)
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What is happening as a cell is in Rapid Repolarization?
- K+ goes out fast (more negative)
- T wave (relative refractory period)
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What happens to a cell when is it at resting membrane potential?
sodium potassium pump is regulating
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Refractory period?
during which cardiac cells may or may not depolarize due to an electrical stimulus
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Absolute Refractory Period (ARP)?
- Onset of QRS complex to the peak of the T wave
- Cannot be stimulated to depolarize
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Relative Refractory Period (RRP)
- Peak of T wave to the end
- Sufficient repolarization that a strong stimulus will depolarize cells
- Vulnerable period of repolarization
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Supernodal Period
End of the T-wave
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Automaticity of cardiac cells?
- Ability of pacemaker cells to spontaneously initiate electrical
- impulse without stimulation from outside source
- SA node, AV node, Purkinje fibers
- Normal Na+, Ca2+, and K+ necessary
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Irritability of cardiac cells?
- Ability to respond to external stimulus (chemical, electrical or
- mechanical)
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Conductivity of cardiac cells?
Ability to receive stimulus and conduct to an adjacent cell (Intercalated disks)
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Contractility of cardiac cells?
Ability to shorten and produce force
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S-A Node?
- “Natural pacemaker" of your heart because it
- controls your heart rate.
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What is the S-A node made of and where is it located?
- Bundle of specialized cells
- In your right atrium connected directly to atria
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How many electrical signals does the S-A node produce per
minute?
- Normally produces 60-100 electrical signals per
- minute
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Internodal pathway
- Bachmann’s Bundle: anterior internodal pathway
- Wenckebach’s bundle: middle
- Thorel’s pathway: posterior
- 50 ms SA node to AV node conduction
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Atrioventricular Junction?
- delays relay of impulse to allow atria time to empty
- (includes AV node and bundle of His)
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What is the AV Node made of and where is it located?
bundle of specialized cells located posterior septal wall of right atrium behind tricuspid valve near the coronary sinus.
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Bundle of His? (and how many bts/min bidcharge?)
- only electrical connection between atria and ventricles.
- Automaticity: 40 – 60 bts/min discharge
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What is the point of the AV delay?
Allows the artria to empty completely
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Where is the His-Purkinje System located and what does it do?
located in ventricals, makes your ventricles contract.
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Accessory pathway
allows for a shortcut for impulses can become dangerous if heartrate increases or etc.
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The parts of the His-Purkinje system include:
- Bundle of His (the start of the system)
- Right bundle branch
- Left bundle branch
- Purkinje fibers (the end of the system)
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Where is the Right bundle branch located?
right ventricle
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three branches of the left bundle branch?
- o Anterior fascicle
- o Posterior fascicle
- o Septal fascicle
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What are Purkinje Fibers are branches of?
The bundle branch that spread through the interventricular septum into the myocardium
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Enhanced automaticity?
- increased firing rate from another pacemaker site other than the SA node
- spontaneous depolarization of non-pacemaker cells
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What is the intrinsic rate of the bundle branches?
20 to 40 bts/min
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Causes of Arrhythmias?
- o Enhanced automaticity
- o Reentry
- o Escape beats (protective)
- o Conduction disturbances (i.e.: AV block)
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What is Reentry?
- Have to have Circular conduction pathway
- o Block within the circuit
- o Delayed conduction with the remainder of the circuit.
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Waveform
positive or negative deflection from the baseline
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What is a segment?
- a line between to waveforms
- o PR segment
- o ST segment
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What is an Interval?
- waveform + segment
- o P-R interval
- o Q-T interval
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What is a complex?
several waveforms
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