Cardiology Intro/Electrophysiology Flashcards
(31 cards)
What are the 3 types of cardiac cells?
Myocardial cells
Pacemaker cells
Conduction cells (purkinje)
Function of myocardial cells
Contraction and impulse conduction
What type of cells exhibit automatic rhythmical electrical discharge in the form of action potentials? (dictate heart rhythm)
Pacemaker cells
What type of cells conduct the action potentials through the heart, providing an excitatory system that controls rhythmic beating?
Conduction cells (purkinje)
What makes the myocardium a functional syncytium?
Doesn’t morph together to form one multinucleated cell like skeletal muscle does, but is able to function as a single unit due to presense of intercalated discs.
What are the crossbands at the end of each myocardial cell called?
Intercalated discs
Types of junctions at intercalated discs
Gap junctions: longitudinal surface. Allow rapid diffusion of ions and AP to travel from cell to cell (functional syncytium)
Desmosomes: transverse surface. Hold cells together and provide mechanical strength.
What are the main Ca++ sources for cardiac muscle contraction?
Ca++ is derived from both the ECF and the SR. SR is not developed enough to provide enough Ca++ on its own.
Different action potentials in the heart
Pacemaker potential
Atrial/ventricular cell potential
Characteristics of pacemaker potentials
Potential gradually becomes less negative until it reaches the threshold.
Characteristics of atrial/ventricular potentials
AP are longer than those in nerve and other muscle cells (300ms vs 3ms in skeletal)
What is the normal pacemaker of the heart?
Sinoatrial (SA) node located in the right atrium
initiates action potential
Where are the backup pacemakers of the heart?
AV node
His-purkinje system
Why is the SA node the main pacemaker?
Discharges faster than the other cells (70-80x per min)
AV node: 40-60x per min
Purkinje fibers: 15-40x per min
Where is the SA Node located?
In the right atrium, below the opening for the cranial vena cava.
Fibers are continuous with atrial muscle fibers, allowing AP to spread immediately into the atrial muscle wall.
Where does the action potential go after the SA node?
Through atrial muscle wall to the AV node, where it is delayed to allow the atria to completely empty their blood into the ventricles before ventricular systole.
Where is the AV node located?
Posterior wall of the right atrium, behind the tricuspid valve.
Has less gap junction permeability, so it more resistant to conduction (delayed response)
What cells transmit the AP after the AV node?
Purkinje fibers lead impulse from the AV node to the AV bundle (bundle of His), and into the ventricles.
How does transmission of the AP in the ventricles compare to that of the atria?
Much faster in the ventricles. Not delayed as it is in the atria.
*Transmission through the remainder of the ventricular muscle is instantaneous
What keeps the electrical impulse from traveling through abnormal routes?
A fibrous skeleton surrounds the atrial muscle.
Impulses can only be transmitted from atrium to ventricle.
How far do the branches of the AV bundle extend?
Down beneath the endocardium to the apex of the ventricles and wrap around, heading back up to the base of the heart.
*Purkinje fibers penetrate and become continuous with the muscle.
Because the cardiac muscle wraps around the heart in a double spiral, how do the atria and ventricles contract?
Atria squeeze inward
Ventricles shorten upward
What is responsible for the slow depolarization of the sinus node?
Pacemaker cells lack normal, fast Na+ channels.
Funny Na+ channels (lf or f) close during AP and open spontaneously after AP finishes, which starts the cycle of depolarization again.
Cause progressive increase in Na+ permeability, and Na+ enters from ECF to lead membrane to threshold again.
How does the closing of the K+ channels assist in depolarization in the sinus node?
Closing of K+ channels at the end of each repolarization keeps K+ inside the cell, making the potential more positive, and leading to another AP.
