Phys - cardiac muscle Flashcards
The prevent tetany of cardiac muscle contraction ___
The duration of contraction is roughly the same as the duration of the AP
Cardiac contractility the is an increase in force generation due to ___
Altered Ca kinetics
The phase 2 plateau of the cardiac myocyte AP is related to a balance between ___
Movement of K out and Ca in
Function of phospholamban
Decrease Ca reuptake
*to increase Ca reuptake you must phosphorylate phospholamban
NE increases cardiac contractility by ___
Phosphorylation L-type Ca channels
Cardiac relaxation requires ___
Removal of Ca from cytosol
ATP to break actin-myosin bond
Membrane repolarization
Atrial vs ventricular transmission of impulses
- Atria have end to end and side to side (horizontal intercalated discs). No t tubules.
- Ventricles have end to end (perpendicular intercalated discs)
Cardiac AP:
Phase 4
Equilibrium for K (-90mV)
IK1
Inward rectifying K current
-responsible for stable, low resting membrane potential
Cardiac AP:
Phase 0
Rapid depolarization Due to Na channels and then Ca channels gNa - rapid increase (conductance) -H gates are open -also have Ca channels, L and T both open
Ca channels closing
CaT close early
CaL close late
Cardiac AP:
Phase 1
- K repolarization is due to K outflow and Cl inflow
- Ito1 and Ito2 open rapidly and close rapidly, leads to phase 2
Cardiac AP:
Phase 2
Plateau
-relatively equal movement of positive charges in and out of the cell
Cardiac AP:
Phase 3
Ca channels close so repolarization takes place, membrane potential drops, and then you get the relative refractory period
In phase 3, m gates are ___ and h gates are ___
Closed (mid phase 3)
Opening (towards end of phase 3)
The absolute refractory period takes place during phase ___ because ___
2, the inactivation gates of Na channels are closed
-the m gates start to close and the H gates are also closed so the channel is inactivatable
The relative refractory period takes place during phase ___ because ___
3, h gates start to open
In the vulnerable period ___
The smallest of stimuli can cause an AP, after phase 3 (aka supranormal period)
H gate positions during each phase?
M gates?
0- both open
1, 2- m open, h closed
3- m closed, h opening
4- m closed, h open
T tubules:
atria vs ventricles
Atria have little or none
Ventricles have a lot
What causes Ca release from the SR?
Trigger Ca from the extracellular space coming in and binding with RYR channels
How to speed up Ca reuptake
Phosphorylation of phospholamban which activates SERCA
- positive lusitropic effect (relaxation)
- inhibiting the inhibitor
SERCA
Pumps Ca back into SR
-removes Ca from sarcoplasm
___ breaks the actin-myosin bond
ATP
Repolarization of the membrane is due to
K efflux
Passive tension prior to contraction
- due to what?
- what determines it in cardiac muscle
Preload
- due to series and parallel elastic elements
- end diastolic volume and pressure (as blood comes into the heart the ventricle stretches. The end-diastolic volume is the volume in the ventricle right before it contracts)
Active force after contraction
-what is it in the heart?
Afterload
-pressure ventricle pumps against (aortic/diastolic pressure)
Internal shortening, but no external shortening in the heart
Isovolumic (no change in ventricular volume)
Cardiac muscle ejection (stroke volume) is what type of muscle contraction?
Auxotonic
- really it is isotonic
- let’s just call it a shortening contraction
Frank starling law of the heart
Blood stretches the heart, increased by venous return, increased preload, more force, more ejection, greater stroke volume.
The inotropic state of the myocardium determines force generation
Contractility
*its all about the amount of Ca in the cytosol
Heavier load = ____
Slower muscle shortening
Increasing cardiac contractility is called a ___
Positive inotropic effect
*phosphorylation of phospholamban, RYR channels, and L type Ca channels in the membrane ALL increase Ca levels
Epinephrine and norepinephrine cause a ____ inotropic effect
What else does this?
Positive
- beta 1 agonists, sympathetic stimulation
- MORE Ca IN THE CYTOSOL
A change in contractility also can change ___
Vmax
Maximum isometric force
*both increase
