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