Phys - cardiac muscle

Question 1

The prevent tetany of cardiac muscle contraction ___

Answer 1

The duration of contraction is roughly the same as the duration of the AP

Question 2

Cardiac contractility the is an increase in force generation due to ___

Answer 2

Altered Ca kinetics

Question 3

The phase 2 plateau of the cardiac myocyte AP is related to a balance between ___

Answer 3

Movement of K out and Ca in

Question 4

Function of phospholamban

Answer 4

Decrease Ca reuptake

*to increase Ca reuptake you must phosphorylate phospholamban

Question 5

NE increases cardiac contractility by ___

Answer 5

Phosphorylation L-type Ca channels

Question 6

Cardiac relaxation requires ___

Answer 6

Removal of Ca from cytosol
ATP to break actin-myosin bond
Membrane repolarization

Question 7

Atrial vs ventricular transmission of impulses

Answer 7

• Atria have end to end and side to side (horizontal intercalated discs). No t tubules.
• Ventricles have end to end (perpendicular intercalated discs)

Question 8

Cardiac AP:

Phase 4

Answer 8

Equilibrium for K (-90mV)

Question 9

IK1

Answer 9

Inward rectifying K current

-responsible for stable, low resting membrane potential

Question 10

Cardiac AP:

Phase 0

Answer 10

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

Question 11

Ca channels closing

Answer 11

CaT close early

CaL close late

Question 12

Cardiac AP:

Phase 1

Answer 12

• K repolarization is due to K outflow and Cl inflow

- Ito1 and Ito2 open rapidly and close rapidly, leads to phase 2

Question 13

Cardiac AP:

Phase 2

Answer 13

Plateau

-relatively equal movement of positive charges in and out of the cell

Question 14

Cardiac AP:

Phase 3

Answer 14

Ca channels close so repolarization takes place, membrane potential drops, and then you get the relative refractory period

Question 15

In phase 3, m gates are ___ and h gates are ___

Answer 15

Closed (mid phase 3)

Opening (towards end of phase 3)

Question 16

The absolute refractory period takes place during phase ___ because ___

Answer 16

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

Question 17

The relative refractory period takes place during phase ___ because ___

Answer 17

3, h gates start to open

Question 18

In the vulnerable period ___

Answer 18

The smallest of stimuli can cause an AP, after phase 3 (aka supranormal period)

Question 19

H gate positions during each phase?

M gates?

Answer 19

0- both open
1, 2- m open, h closed
3- m closed, h opening
4- m closed, h open

Question 20

T tubules:

atria vs ventricles

Answer 20

Atria have little or none

Ventricles have a lot

Question 21

What causes Ca release from the SR?

Answer 21

Trigger Ca from the extracellular space coming in and binding with RYR channels

Question 22

How to speed up Ca reuptake

Answer 22

Phosphorylation of phospholamban which activates SERCA

• positive lusitropic effect (relaxation)
• inhibiting the inhibitor

Question 23

SERCA

Answer 23

Pumps Ca back into SR

-removes Ca from sarcoplasm

Question 24

___ breaks the actin-myosin bond

Answer 24

ATP

Question 25

Repolarization of the membrane is due to

Answer 25

K efflux

Question 26

Passive tension prior to contraction * due to what? - what determines it in cardiac muscle

Answer 26

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)

Question 27

Active force after contraction | -what is it in the heart?

Answer 27

Afterload | -pressure ventricle pumps against (aortic/diastolic pressure)

Question 28

Internal shortening, but no external shortening in the heart

Answer 28

Isovolumic (no change in ventricular volume)

Question 29

Cardiac muscle ejection (stroke volume) is what type of muscle contraction?

Answer 29

Auxotonic - really it is isotonic - let's just call it a shortening contraction

Question 30

Frank starling law of the heart

Answer 30

Blood stretches the heart, increased by venous return, increased preload, more force, more ejection, greater stroke volume.

Question 31

The inotropic state of the myocardium determines force generation

Answer 31

Contractility | *its all about the amount of Ca in the cytosol

Question 32

Heavier load = ____

Answer 32

Slower muscle shortening

Question 33

Increasing cardiac contractility is called a ___

Answer 33

Positive inotropic effect | *phosphorylation of phospholamban, RYR channels, and L type Ca channels in the membrane ALL increase Ca levels

Question 34

Epinephrine and norepinephrine cause a ____ inotropic effect What else does this?

Answer 34

Positive - beta 1 agonists, sympathetic stimulation * MORE Ca IN THE CYTOSOL

Question 35

A change in contractility also can change ___

Answer 35

Vmax Maximum isometric force *both increase