Flashcards in Cardiac Action Potential Deck (31):
What all does the AP from the SA node go through?
spreads throughout atria causing depolarization (RA slightly before LA); spreads down to the AV node
Describe the path of the AP from the AV node through the ventricles
AV node -> bundle of His -> right and left bundle branches in the interventricular septum -> down towards apex of heart and turns and moves back up along the lateral walls of the ventricles through Purkinje fibers
Why are nerve fiber sizes in the heart important? Describe the order from large to small
larger fibers have faster AP transmission & greater velocity
Purkinje fibers/bundle branches/bundle of His > atria and ventricular myocytes > AV node
What is the purpose of the conduction delay at the AV node?
to allow atria to completely empty into ventricles before ventricles contract
What is resting membrane potential of the SA node?
-65 +/- (-5)
What is resting membrane potential of the atria and ventricles?
-90 +/- (-5)
Describe Na (m) channels
voltage gated Na channels that open to depolarize the cell during phase 0 (activated when membrane potential crosses threshold); contribute to phase 1 as well (inactivation gates close)
Describe K (a) channels)
produce a transient outward current during phase 1; open briefly to cause partial repolarization (balancing act w/ Na (m) channels
Describe L type Ca channels
voltage gated Ca channels that open after depolarization spike and bring Ca into the cell; establish plateau of phase 2 w/ K (b) channels; closing causes phase 3
Describe K (b) channels
allow K out of cell except from phase 0 to phase 3; slow to close but prevent K from leaking out of cell too much as a result of Na influx
Describe K (c) channels
K leak channels are always open and contribute to resting membrane potential
Describe Na (f) channels
specific to the SA and AV nodes; cause slow depolarization during resting phase (allows nodes to have autonomous depolarization)
Describe K (d) channels
voltage gated K channels; open and release K during phase 3 (repolarization)
What causes phase 4 of the SA and AV nodes? What happens if the slope changes?
Phase 4 caused by Na (f) channels
If slope increases -> faster depolarization
If slope decreases -> slower depolarization
What causes phase 0 of SA/AV node?
L type Ca channels open (Ca influx) and K (b) channels close
What causes phase 3 of SA/AV node?
closing of L type Ca channels and opening of K (b) channels (reverse of phase 0)
What do fast tissues involve for cardiac AP?
myocytes and Purkinje fibers
What sustained resting membrane potential in phase 4 of fast tissues?
K (c) channels - leak channels continuously allow K out of cell
What causes phase 0 of fast tissues?
depolarization caused by crossing threshold; voltage gated Na (m) channels open
What causes phase 1 of fast tissues?
small repolarization caused by Na (m) channels closing and K (a) channels opening -> pulls potential down a little bit
What causes phase 2 of fast tissues?
plateau phase -> sustained by slow opening of L type Ca channels which delays repolarization; balances w/ closure of K (b) channels to maintain plateau (sustain contraction)
What causes phase 3 of fast tissues?
complete repolarization caused by closing of L type Ca channels and reopening of K (b) channels and opening of voltage gated K (d) channels
What is absolute refractory period (ARP)?
no depolarization can occur
What is relative refractory period (RRP)?
when an AP can be generated but the cell will have abnormal conduction (AP is weaker)
What is supernormal period (SNP)?
when the cell is more excitable than normal but will have a lower phase 0 slope (slower velocity)
Describe chronotropic effect
changes rate of depolarization of SA node (affects HR)
Positive = faster HR
Negative = slower HR
Describe dromotropic effect
changes speed of conduction
Positive = increased speed
Negative = decreased speed
Describe inotropic effect
changes strength of muscular contraction
Positive = heart contracts harder
Negative = heart contracts softer
Describe lusitropic effect
changes rate of muscular relaxation
Positive = increased relaxation
Negative = decreased relaxation
What carries parasympathetic fibers to the SA and AV nodes? Describe the receptors and NT involved in parasympathetics of the heart
Vagus N. carries parasympathetics to SA and AV node
NT = ACh
Receptor = muscarinic (M2 or M3)