Cardiac muscle phys Flashcards
unique histology of cardiac myocytes
intercalated disks connect fibers: desomsomes, fascia adherens, and gap junctions
major exception to gap junction communication in cardiomyofibers
no gap junctions b/w atrial myocytes and ventricular
pathway of depolarization in the heart
SA node- atria- AV node- bundle of His- left and right branching bundles- purkinje fibers
AV node rate of conduction
slower than SA node, allows for delay b/w atria and ventricles and allows more time for ventricular filling
spread of ventricular contraction
starts in apex, spreads to walls- almost simultaneous b/w ventricles
conduction b/w heartbeats
no APs, pacemakers are depolarizing (If channels)
phases of ventricular AP
4=resting potential 0=upstroke, rapid depolarization 1=partial repolarization 2=plateau 3=rapid repolarization
channel at phase 4 for VAP
leaky IR K channels, maintain resting potential
phase 0 channels in VAP
voltage gated Na+ fast channels open, IR K blocked
phase 1 channels in VAP
Na+ fast channels inactivating, L-type/DHP Ca++ begin to open, transient outward K+ open
phase 2 channels in VAP
L-type Ca++ open, DR K+ begin to open, transient outward K+ inactivating, Na+ fast channels inactive
phase 3 channels in VAP
L-type Ca++ inactivating, DR K+ open, transient outward K+ inactive
unique feature of excitation-contraction coupling w/ cardiac myocytes
SR is not directly adjacent to T-tubules, process is “calcium induced calcium released” as cytosolic Ca++ stimulates ryanodine receptors and Ca++ release from SR
mechanisms for lowering cytosolic Ca++
SERCA pumps on SR, Ca++/Na+ exchanger on sarcolemma (dependent on Na+ concentration gradient), Ca++ ATPase on sarcolemma
phases present in pacemaker action potentials
phase 0= upstroke
3=rapid repolarization
4=slow depolarization! not resting membrane potential, this is responsible for automaticity
