Excitation Contraction Coupling Cardia Cycle

Question 1

What happens when you add increasing doses of Diltiazem (a Ca channel blocker) to a cell?

Answer 1

Ca channels that open during phase 2 are blocked → plateau phase of AP gets shorter → contraction of muscle gets increasingly shorter

Question 2

What is Ca that comes in during the plateau phase important to?

Answer 2

Contraction of cardiac muscle

Question 3

What happens to the twitch force of a cell when you add increasing doses of Diltiazem?

Answer 3

It decreases

Question 4

Define: sarcolemma

Answer 4

outer-cell membrane

Question 5

Define: T-tubule

Answer 5

invagination of cell membrane that goes deep in muscle and communicates with EC space.

Question 6

How does the AP open Ca channels along the membrane?

Answer 6

AP travels along the cardiac muscle and down the T-tubule when the cardiac muscle depolarizes → Ca channels open along the membrane

Question 7

Where is Ca stored inside the cell?

Answer 7

Sarcoplasmic reticulum

Question 8

When do Ca Channels open?

Answer 8

when there is a voltage change between -10 mV and +10 mV

Question 9

What is the main mechanism for getting Ca from the cytosol back into the SR?

Answer 9

ATPase pump

Question 10

How does extracellular Ca aid in muscle contraction?

Answer 10

Ca channel opens → Ca flows in → Ca binds to rhyinadine channels → allows Ca to flow from SR into cytoplasm → intracellular Ca concentration increases → contraction

Question 11

How does the membrane voltage increase from -10 mV to 10 mV?

Answer 11

Fast sodium channels open

Question 12

How do Catecholamines function in muscle contraction?

Answer 12

E or NE bind β₁ receptor → causes activation of adenylyl cyclase → increases cyclic AMP → stimulates cAMP-PK → Phosphorylates Phospholamban and Troponin → enhance relaxation of muscle

Question 13

What happens when phospholamban is phosphorylated?

Answer 13

it decreases inhibition → enhances activity of Ca pump → pumps Ca back into SR faster

Question 14

What is phospholamban?

Answer 14

Regulatory protein that inhibits Ca pump

Question 15

What happens when Troponin I is phosphorylated?

Answer 15

it has reduced affinity for Trp C for Ca → Ca still binds but not as tightly → Ca is releases from Troponin more quickly

Question 16

How do catecholamines affect the cardiac muscle?

Answer 16

It makes them more efficient in handling Ca → more efficient in contracting, creating pressure, and pumping out greater SV

Question 17

What happens when a Ca channel is phosphorylated?

Answer 17

It stays open longer and conducts more Ca → more efficient contraction b/c more Ca in cell

Question 18

What does the Ca pump do to the cardiac muscle cell?

Answer 18

it uses ATP to remove Ca from the cytosol and put it in the EC

Question 19

What does the Na-Ca exchanger pump do to the cardiac cell?

Answer 19

It removes Ca from the cell by exchanging 3 Na for 1 Ca

Question 20

What do Cardiac Glycosides do to cardiac muscle cells?

Answer 20

they inhibit Na-K pump which results in intracellular Na+ accumulation

Question 21

What is the resulting effect of a Cardiac glycoside?

Answer 21

Na concentration outside cell decreases

less sodium gradient to exchange Na for Ca

more calcium in cell

Increased calcium in cell promotes a better contraction in the ventricle

dont enhance relaxation

Question 22

Define: Systole

Answer 22

Contraction and shortening

Question 23

Define: Diastole

Answer 23

Relaxation and refilling

move calcium back into storage

Question 24

What is the equation for Cardiac Output?

Answer 24

CO = HR X SV

Question 25

How can you increase HR using the autonomic nervous system?

Answer 25

by stimulating sympathetic nervous system

Question 26

How does Ca cycling influence SV?

Answer 26

it increases it

Question 27

What governs the systolic phase of Ca cycling?

Answer 27

AP (depolarization in the heart) → Ca channels open, firing of SA node causes depolarization

Question 28

In general, how does Ca effect muscle contraction?

Answer 28

Ca binds to Troponin C → troponin moves and uncovers myosin binding site → myosin binds to actin → shortening occurs → contraction

Question 29

What effect does ACh have on the contractile force of the heart?

Answer 29

Decrease HR Decrease force of contraction Decrease SV by reducing Contraction

Question 30

What effect does NE have on the contractile force of the heart?

Answer 30

Increases contractile force increases SV

Question 31

What is the mechanism behind Calcium induced Calcium release?

Answer 31

Ca ions bind to a channel protein on SR, opening a channel and allows Ca out of storage into cytoplasm

Question 32

What increases SV?

Answer 32

Contractility Preload

Question 33

How does afterload effect SV?

Answer 33

it reduces it

Question 34

How do contractility and Preload effect CO?

Answer 34

they increase ut

Question 35

What does afterload do to CO?

Answer 35

limits CO

Question 36

What happens to SV as you increase afterload?

Answer 36

it inhibits SV

Question 37

Define: Preload

Answer 37

the force present in a relaxed muscle (measure of how close you are to optimal length)

Question 38

Define: Optimal Length (L_o)

Answer 38

length at which you get max contraction in skeletal muscle get max shortening

Question 39

is preload fixed in the heart?

Answer 39

no

Question 40

What determines Preload in vitro?

Answer 40

it varies with resting length of muscle

Question 41

What determines Preload in vivo?

Answer 41

venous pressure and end diastolic volume

Question 42

Define: End Diastolic Volume (EDV)

Answer 42

amount of blood in ventricle at end of filling phase

Question 43

What determines preload?

Answer 43

amount of blood that fills ventricles prior to being stimulated to contract

Question 44

What does the preload force set?

Answer 44

the length of the resting muscle

Question 45

Why does cardiac muscle operate at less than its optimal legth?

Answer 45

the more it is filled the better it contracts until it gets to a certain length if you over stretch it, function starts to drop off

Question 46

Define: Frank-Starling Relationship

Answer 46

The sequential increase in output by putting more blood in the ventricle

Question 47

What happens as more preload is added to the ventricle?

Answer 47

The ventricle will contract more efficiently

Question 48

Define: Afterload

Answer 48

The force exerted by a shortening muscle (force that opposes shortening of muscle) (i.e. the weight you hold)

Question 49

What is the afterload of the right ventricle?

Answer 49

pulmonary artery

Question 50

What is the afterload of the Left Ventricle?

Answer 50

aorta

Question 51

How is afterload determined in vitro?

Answer 51

by the applied load

Question 52

How is afterload determined in vivo?

Answer 52

by arterial pressure (systemic arterial pressure for the left ventricle (aorta) and pulmonary arterial pressure for the right ventricle

Question 53

What does the RV empty its blood contents?

Answer 53

When it overcomes the pressure of pulmonary artery to open the pulmonic valve

Question 54

What does the LV empty its blood contents?

Answer 54

when it overcomes the pressure of the aorta to open the aortic valve

Question 55

Define: Contractility (Inotropy)

Answer 55

The variable state of muscle performance at a given muscle length The ability to increase cardiac function not dependent on length

Question 56

What do most pathways that regulate contractility involve?

Answer 56

Ca++

Question 57

what is the relationship between contractility, length, and preload?

Answer 57

Contractility is independent of length and preload

Question 58

What is the result of contractility being independent of length and preload?

Answer 58

no matter what the preload of a muscle is at, the max velocity of shortening comes back to the same point no matter what the length of your muscle is stretched to, if you increase contractility, you can make muscle contract more efficiently

Question 59

what is contractility distinguished from in muscle performance?

Answer 59

length-dependent changes

Question 60

How do you increase contractility?

Answer 60

increase Ca content

Question 61

What happens to SV if you increase contractility?

Answer 61

it increases

Question 62

What is contractility determined by?

Answer 62

dP/dt | (rate at which pressure increases)

Question 63

Define: Chronotrope

Answer 63

anything that effects heart rate

Question 64

Define: Positive Chronotrope

Answer 64

increases heart rate (sympathetic nervous system stimulation [release of NE or E])

Question 65

Define: Negative Chronotrope

Answer 65

decreases heart rate | (ACh → binds muscarinic receptor)

Question 66

Define: Inotrope

Answer 66

influences contractility

Question 67

Define: Positive inotrope

Answer 67

increases contractility (NE, E bind β₁ receptors and enhance Ca cycling

Question 68

Define: Negative Inotrope

Answer 68

Decreases contractility → ACh

Question 69

What is parasympathetic (chronotrope/inotrope)?

Answer 69

Negative Chronotrope Negative Inotrope

Question 70

What is sympathetic (chronotrope/inotrope)?

Answer 70

positive chronotrope positive inotrope

Question 71

Equation: Ejection Fraction

Answer 71

EF = EDV - (ESV/EDV) → EF = SV/EDV

Question 72

Define: Ejection Fraction

Answer 72

% of blood in ventricle that gets ejected each time heart beats (ratio of the volume of blood ejected from LV per beat (SV) to the volume of blood in the LV at the end of diastole (EDV)

Question 73

Define: End diastolic volume (EDV)

Answer 73

max volume in ventricle prior to contraction

Question 74

Which one of the following would most likely occur as a direct result of applying a Ca++ channel blocker to a ventricular myocyte? A. no effect B. An increase in contractility C. an increase in HR D. a reduction in the duration of phase 2 of the action potential E. Loss in phase 1 of the action potential

Answer 74

D. a reduction in the duration of phase 2 of the action potential

Question 75

In contracting calcium muscle, calcium… A. is present in an amount that usually saturates all intracellular calcium binding sites B. comes from both the extracellular space and from the SR C. enters the cell during the rapid upstroke (phase 0) of the AP D. all of the above E. none of the above

Answer 75

comes from both the extracellular space and from the SR

Question 76

The Frank-Starling Relationship… A. Explains the effect of ACh on ventricular performance B. Explains the relationship between afterload (wall stress) and maximum +dP/dt C. Is determined during isovolumic contraction D. Explains the influence of positive inotropic agents on cardiac function E. None of the above

Answer 76

E. None of the above