Cardiac Mm

Front 1

What allows for a long refractory period in cardiac mm?

Back 1

Plateau

Front 2

What is the source of Ca in cardiac mm? How is this different from sk mm?

Back 2

Cardiac mm: extracellular Ca
Sk mm: intracellular Ca from SR

Front 3

How is the depolarization wave spread in cardiac mm? How is it spread in sk mm?

Back 3

Cardiac mm uses gap junctions so depolarization comes from neighboring cell.
Sk mm has T tubules that propagate the depolarization into the mm.

Front 4

What is calcium induced calcium release?

Back 4

Ca from extracellular sources induces Ca from the Sr to be released in cardiac mm. (Ca induces RyR receptors)

Front 5

What is the mech that allows actin/myosin binding in cardiac mm

Back 5

Ca binds troponin, just like Sk mm!

Front 6

What are two ways Ca is cleared from cardiac mm. What is the result from decreased Ca

Back 6

1. SERCA: ATPase on SR
2. 2nd Active Transport: Ca leaves and Na enters the cell

When Ca decreases it no longer binds troponin so Actin/Myosin cant bind.

Front 7

How many AP in autorythemic cells are needed to elicit 1 AP in contractile cells?

How does an AP reach contractile cells?

Back 7

1

**the AP in autorhythmic cells are carried by PK fibers to the contractile cells. The AP spreads through contractile cells via gap junctions in intercalated disk

Front 8

Trace the conduction path of the heart

Back 8

SA
AV
Bundle of HIS
R/L Bundle Branch
PK Fibers

Front 9

What mechanical event follows atrial depolarization?

Back 9

Atrial Contraction?

Front 10

What allows depolarization to spread rapidly among the contractile cells of the heart?

Back 10

Intercallated disks

Front 11

Do autorhythmic cells do mechanical work?

Back 11

NO

Front 12

What increases the force of contractility of cardiac mm?

Back 12

Ca

Front 13

What is a distinguishing characteristic of cardiac mm?

Back 13

it has intrinsic control

Front 14

Does Cardiac mm rely on motor neurons?
What mechanism allows this?

Back 14

NO
the AP generated by AR cells frees the heart from needing motor neurons

Front 15

Intercalated disks are made of what two features. What is the function of each

Back 15

1. Desmosomes: resist mechanical force

2. Gap junctions: eletrical coupling, cytoplasm is continuous

Together, these allow the cardiac mm to act as a single unit

Front 16

What are the major cell types in cardiac mm?

Back 16

1. Contractile Cells: more abundant, respond to depolarization by contracting, do the mechanical contraction, AP has a characteristically long refractory period, Fast AP

2. Autorhythmic (conductile) Cells: rapid spread of eletrical signal, conducting system, dont contract, initiate and propagate the AP that triggeres contraction, 'pacemaker', myogenic, self excitable, gives rise to a coordinated rhythmic pumping, Slow AP

Front 17

When is a contractile cell stimulated, what happens at stimulation?

Back 17

contractile cell is stimulated by an AR cell. At this time ALL channels are stimulated to open, but do so at differing speeds

Front 18

In AR cells what ion channel allows AP generation (depolarization) once threshold has been reached

Back 18

L type Ca channels

Front 19

What leads to depolarization in AR cells

Back 19

F type Na channels open
T type Ca channels open (L type open at threshold to cause upstroke)
K channels close

Front 20

name the 4 ion channels involved in AP of AR cells

Back 20

T type: transient Ca. When these open, Depolarization
F type: funny Na. When these open, Depolarization
L type: long lasting Ca. Generates depolarization of AP (upstroke), close during repolarization
K+. Open to repolarize the cell

Front 21

Describe the general characteristics of the AP for a contractile cell.

time
resting potential
refractory period

Back 21

long period of time!
stable resting potential
LONG refractory period to ensure NO tetnus

Front 22

What occurs during phase 0 of an AP created by contractile cells?

Back 22

this is the upstroke of the AP

Na enters the cell

cell is DEPOLARIZED

**recall in AR cells phase 0 occurs due to Ca entering the cell

Front 23

What occurs during phase 1 of an AP created by contractile cells?

Back 23

breif repolarization due to a little K (fast K channels)leaving the cell and Na channels closing

Front 24

What occurs during phase 2 of an AP created by contractile cells?

Back 24

plateau period: inward/outward currents are about equal
Responsible for the LONG AP seen in cardac contractile cells

Ca will enter the cell
K leaves the cell

Front 25

what is the major difference btwn cardiac contractile cell AP and sk mm AP?

Back 25

Phase 2 PLATEAU. the cardiac cells have a period when Ca into the cell is about equal to the K out of the cell so there is a broad flat peak in the AP. This ensures cardiac cells will NOT have tetnus

Front 26

Ca inhibitors will block which phase of AP in contractile cells?

Back 26

phase 2
plateau

Front 27

What occurs during phase 3 of an AP created by contractile cells?

Back 27

Repolarization!

Ca no longer enters the cell
K leaves the cell to hyperpolarize the cell to resting

Front 28

What occurs during phase 4 of an AP created by contractile cells?

Back 28

Resting membrane potential

Front 29

How long does a mm contraction take in relation to the AP that generated it (contractile cells). What does this mean and why is it important to have this response?

Back 29

the contraction lasts longer than the AP

ie by the time the AP is over the mm is just finishing up contraction, this restricts summation and tetnus in cardiac mm. Good so that mm can contract AND relax: its a pump!

Front 30

What does an AP in a contractile cell elitic?

Back 30

a mm contraction

Front 31

Where are the AR cells that conduct AP located?

Back 31

SA node

Front 32

What is the pacemaker of the heart? What is a unique feature?

Back 32

SA node
Unstable resting membrane potential

Front 33

Why is the pacemaker of the heart the SA node?

Back 33

the SA node has the highest rate of intrinisic depolarization (HR)

Front 34

Name 3 differences in the AP of contractile cells vs AR cells

Back 34

1. automaticity in AR only
2. Plateau in contractile only
3. unstable resting membrane potential in AR only

Front 35

What phases are missing in AR AP?

Back 35

1
2

Front 36

What occurs during phase 0 of an AP created by AR cells?

Back 36

upstroke of an AP

caused by Ca entering the cell

**recall an inflow of Na is responsible for phase 0 in contractile cells

Front 37

What occurs in phase 3 of an AP created by AR cells?

Back 37

Repolarization
K leaves the cell
Ca channels close

Front 38

What occurs in phase 4 of an AP created by AR cells?

Back 38

Pacemaker potential: Automaticity
Spontaneous depolarization

Front 39

What causes depolarization of cells in the SA node?

Back 39

Spontaneous depolarization to threshold fires an AP
Pacemaker Potential
F type Na channles (turned on by previous repolarization)
T Ca open at threshold

Front 40

What causes the upstroke of AP in AR cells? Contractile cells? What phase

Back 40

AR: Ca
Contractile: Na
Phase 0

Front 41

The rate of what phase of what AP sets HR

Back 41

Phase 4
AP by AR

**when the slope of the depolarization is more steep more AP will fire and so HR increases

Front 42

From what node does NSR (normal sinus rhythem) occur? What is the BPM for normal conduction

Back 42

SA node
60-100

Front 43

When will a latent pacemaker take over for the heart?

Back 43

When the SA node is blocked

the fastest pacemaker will take over. The pacemaker potential is highest at the begining of the condiction path and slowest at the end of the conduction path
ie SA>AV>Bundle of HIS> R/L bundle branch> PK fibers

Front 44

Is conduction through the AV node slow or fast?

Back 44

Slow

Front 45

Is conduction through the PK fibers slow or fast?

Back 45

fast

Front 46

What does conduction velocity refer to?

Back 46

the spread of an AP through the heart
**conduction velocity has physiological implications

Front 47

name 2 factors that dictate conduction velocity

Back 47

1. upstroke of AP (how membrane pot changes over time)
2. resistance

Front 48

What cardiac cell type fires fast AP?

Back 48

contractile cells

Front 49

What cardiac cell type fires slow AP?

Back 49

Pacemaker (AR cells)

Front 50

Where are T Tubules more developed in the heart?

Back 50

ventricles

Front 51

State the steps of Excitation Contraction Coupling in cardiac mm

Back 51

1. AP brings depolarization down the T tubule
2. L type Ca channels open as part of AP (phase 2, plateau)
3. The L type (DHP) receptors that allow Ca into the cell induce more Ca to enter the cell via RyR on SR
4. Ca binds troponin and moves tropomyosin out of the way
5. Actin/Myosin bind and cross bridging occurs
6. Relaxation occurs when Ca is cleared by SERCA

Front 52

What is the tension/force/contractility of a cardiac mm contraction proportional to?

Back 52

Ca levels!

Front 53

What determines how much Ca is released from the SR

Back 53

Ca induced Ca release

1. amt of Ca in Sr
2. Amt of Ca that enters via L type

Front 54

What contributes to the majority of Ca flux?

Back 54

SERCA pump

Front 55

Name 2 drugs that enhance the force of contraction of cardiac mm?

Back 55

Digitalis
Digitoxin

Front 56

How do digitalis/digitoxin work?

Back 56

They block the Na/K ATPase so that the Na/Ca exchanger works in reverse and pumps Na out of the cell and Ca into the cell.
Increased Ca leads to increased force of contraction

Front 57

In what direction does the Na/Ca exchanger normally work?

Back 57

Allows Na INto the cell along conc grad
Pumps Ca OUT of the cell

Front 58

When the Na/K ATP ase no longer functions what happens to the Na/Ca exchanger?

Back 58

Ca is moved INTO the cell!
This increases the force of contraction of the heart

ex digitalis/digitoxin

Front 59

Does the heart undergo tentus or summation?

How does the heart regulate the force of contraction?

Back 59

NO

strength of contraction increases when cardiac mm fibers are stretched

Front 60

Does cardiac mm work at the optimal length tension relationship?

Back 60

NO

Front 61

What does the force of contraction of cardiac mm rely on?

Back 61

initial fiber length

Front 62

What does increasing the length of a cardiac mm fiber do?

Back 62

1. increases affinity of Ca and troponin
2. Increases release of Ca from SR

Front 63

what is the realtionship btwn ca, length, force?

Back 63

increased ca leads to increased force. ca can be increased by stretching cardiac mm fibers

Front 64

how does contractility alter tension?

Back 64

independent of fiber length

Front 65

positive ionotropic effect

3 examples

Back 65

increasaed contractility and rate of tension at a fixed length

sympathetic NS
catecholamines
HR

Front 66

negative ionotropic effect

2 examples

Back 66

decreased contractility and rate of tension at a fixed length

parasympathetic activity
heart failure

Front 67

what causes faster relaxation in cardiac mm?

Back 67

phospholamban is Pi and increases activity of SERCA

Front 68

What two things will increase the rate of tension development in cardiac mm?

Back 68

1. phosphorylation of Ca channels on the SR increase the Ca that comes into the cell during the Plateau
2. Increased ca induced ca release (increased tension)

Front 69

What is increased peak tension due to in cardiac mm?

Back 69

increased intracellular Ca

Front 70

Where do T tubules and SR meet?

Back 70

Z line

Front 71

is cardiac mm single nuclei or multinucleate

Back 71

SINGLE

Front 72

waht things increase contractility

Back 72

SNS
Catecholamines
HR


Contractility is decreased by:
Heart Failure and PNS


**Recall contractility (inotropism) is a way to increase the force of contraction without changing fiber length, this method increaes Ca to increase contractility