Electrophysiology Flashcards
What are characteristics of cardiac myocytes not present in other muscle cells?
- branching muscle fibers
- cardiac myocytes are connected with intercalated discs
What are the function of intercalated disks? What do they contain?
Allow action potentials to propagate from cell to cell
Gap junctions
What is functional syncitium?
an AP can be induced & depolarization will travel from cell to cell via INTERCALATED DISCS and BRANCHING
aka: entire myocyte mass is depolarized by following the cell before it– cells working together
What prevents tetanization (spasm) of cardiac muscle
cyclic movement of Ca+2
- cells have a moment of rest
What ion channels alter cardiac muscle cell charge?
1) voltage-gated ion channels = Na+, Ca+2, K+
2) ligand-gated ion channels = many K+
3) stretch-activated ion channels
What do stretch-activated ion channels do?
changes the amount of Ca+2 allowed to enter myocyte with each beat
What is the equation for calculating total current?
Total current (I) = N x i x p
What maintains the negative resting membrane potential of cardiac cells?
Sodium Potassium ATPase pump
2K+ in/ 3 Na+ out
Which Ca+ pumps are steady state or opened at depolarization?
1) Na+/Ca+ pump = steady state
Voltage-gated
2) Ca+2 channels (VOCC) = open at depolarization
T or F: nerve and skeletal muscles have the slowest AP duration
F: cardiac myocyte AP duration is the slowest
- due to prolonged period of Ca+2 entry
Four phases of ventricular cardiac myocyte AP
Phase 0: Na+ floods cell - resting potential becomes more (+)
Phase 1: Na channels INACTIVE, some K+ channels leaking outward
Phase 2: VOCC activated - Ca+2 begins entering cell
Phase 3: Ca+2 entering cell decreases, K+ charge being retified
Phase 4: resting membrane
What are the two types of action potentials in myocardial cells?
which type in which cell (pacemaker and contractile myocyte)
Fast response = contractile cells
Atrial myocytes
Ventricular myocytes
Slow response = pacemaker
Sino-Atrial node
Atrio-Ventricular node
Bundle of His and Purkinje fibers
What are the two types of contractile FAST response cells?
Atrial myocytes
Ventricular myocytes
Why are ATRIAL myocytes faster than ventricular myocytes?
- less Ca+2 is needed to contract because it is a lower pressure system than the ventricular myocytes
this means short phase 2
What are the three slow response myocardial cells?
Sino-Atrial node
Atrio-Ventricular node
Bundle of His and Purkinje fibers
What drives phase 4 of slow response action potentials?
interaction of K+/Na+ channels opening and closing
What is the dominate pacemaker of the heart? Where is it located?
Sino-Atrial node
Right atrium
What is the electrical connection between THE ATRIUM
Bachmann’s bundle - connects SA node to the left atrium
What is the AV node? Where is it located?
atrioventricular node - bottom of the right atrium
How does the SA node communicate with the AV node?
3 internodal tracts in the right atrium
How does the atrial electric communicate or connect to ventricular electric?
Describe the branching pattern of the AV node after the bundle of His?
- left and right bundle branch (LBB & RBB)
- left bundle branch branches into anterior & posterior fascicle
- at the end of anterior and posterior fascicles and RBB, there are Purkinje fibers
What are the species differences between locations of Purkinje fibers?
dogs = in endocardium
cows and most other species = diffuse through myocardium
Describe a cardiac pacemaker cell action potential
- depolarization occurs due to Na+ entering and K+ leaving decreases
- Ca+2 begins entering cells and threshold is reached causing AP
What entering the cardiac cells causes the contraction
Ca+
Why are pacemaker cells slower than atrial/ventricular myocytes?
absence of fast Na+ channels during the depolarization period (cells become more positive slower than atrial/ventricular myocytes)
How do acetylcholine and norepineprine change heart rate?
Acetylcholine decreases the rate of depolarization and lengthens the interval between action potentials decreases heart rate
Norepinephrine increases the rate of depolarization and shortens the interval between action potentials increases heart rate
Describe the overall action potential/contraction process of the heart
1) SA node reaches threshold –> AP across right atria to left atria
2) Bachmann’s bundle carries electrical current to left atria (both atrium contract - left slightly slower),
3 internodal tracts communicate with AV node
3) AP travels down AV node through bundle branches to apex of heart, atria done contracting
4) both ventricles contract from Purkinje fibers
What are the two refractory periods present in myocardial cells? Which one is absolute (no AP can be excited)?
1) Effective refractory period (ERP) - absolute - no AP can be excited
2) Relative refractory period (RRP) - strong enough stimuli could produce AP
What happens when AP occur to closely together?
arrhythmias
