Cardiac muscle physiology Flashcards
sarcomere elements
- go from z band to z ban
- thin filament area called the I band
- overlap of filaments is the A band
- thick filament zone is the H band
latent pacemakers
cells other than the SA node exhibiting automaticity
pacemaker rates
-SA>AV>bundle of HIS>purkinje
ectopic pacemakers
latent pacemakers that become the pacemaker of the heart
speed of conduction
purkinje>atria and ventricles> AV node
AV node
delays electrical conduction between the atria and ventricles
equilibrium potentials
- K is -95
- Na is +72
- Ca is +133
- determined by the number of open channels and by electrogenic ion pumps and exchangers
fast reponse action potentials
- contractile myocytes
- atrial and ventricular
slow response action potentials
- pacemaker myocytes
- SA and AV nodes
fast response APs phase 4
- resting Em
- near Ek due to high K+ permeability
- dominated by IK1 (outward current due to activation of inwardly rectifying K channels)
fast response APs phase 0
- rapid depolarization
- mediated by INa (inward current due to activation of voltage-dependent Na channels)
fast response APs phase 1
- transient repolarization
- mediated by Na channel inactivation and activation of transient outward K current (iKto)
fast response APs phase 2
- plateau
- mediated by inward current of Ca due to Ltype voltage gated Ca channles (CGCC) and outwards iK1
fast response APs phase 3
- rapid repolarization
- mediated by iK (outward current due to activation of voltage-dependent K channels)
slow response APs phase 4
- pacemaker potential
- inward funny current (If) carried mainly by Na+
- inward Ca currents mediated by T-Type and L type channels
slow response APs phase 0
- slow depolarization
- mediated by iCaL
slow response Aps phase 3
-mediated by iK (outward current due to activation of voltage-dependent K channels)
conduction system summary
- SA node determines HR
- AV node: low conduction velocity; delays AP propagation between atria and ventricles
- Purkinje fibers: conduct impulses to ventricles leading to ventricular systole
fast response APs summary
- characteristic of contractile myocytes
- stable phase 4; rapid phase 0; phase 2 plateau
slow-response APs
- characteristic of pacemaker myocytes
- unstable phase 4 (pacemaker potential)
- slow phase 0; lack iNa (voltage gated Na channels
excitation-contraction coupling
- altering Ca cytosolic concentrations
- during plataeu phase, L type VGCC open and Ca stimulated CICR on ryanodine receptors
- Ca binds to TnC and contraction occurs
- Ca inhibits the Ltype receptors
- SERCA pumps Ca back into the SR
contraction
-depolarization leads to Ltype VGCC activation
-ryandone receptor is stimulated
=Ca released from SR
-increased Ca concentration
cross bridge cycling
-Ca binds to TN-C on thin filament to initiate contraction
relaxation
- inactivation of L type VGCC
- Ca reuptake to SR via SERCA
- Ca extrusion via the Na/Ca exchanger and Ca ATPase
