Cardiac Muscle Structure

Question 1

Relationship between exercise intensity and CO

Answer 1

Positive

Incr exercise and need of skeletal muscle, incr CO

Question 2

Define Preload

Answer 2

volume in the ventricle before ejection

Question 3

Define afterload

Answer 3

pressure ventricles pushing against to eject blood (usu aortic pressure or pulm HTN)

Question 4

Largest cell population in heart

Answer 4

1) endothelial cells

2) cardiac fibroblasts

Question 5

function of cardiac fibroblast

Answer 5

lay down ECM of heart for myocytes to function

Question 6

most predominant components of ECM

Answer 6

fibrillar collagen type 1 and 3

Question 7

Unique features of skeletal muscle

Answer 7

1) striated
2) not under direct neural control (like skeletal)
3) muscle shorter, narrower, richer in mitochondria than skeletal
4) ATPase activity of myosin slower in cardiac
5) Ca2+ binding to troponin C regulates actomyosin

Question 8

cardiac muscle cells connected with each other through ____

Answer 8

intercalated discs

Question 9

each cardiac muscle is from __ to __ and contain ___ and ___

Answer 9

z disc to z disc

contain desmosomes and gap junctions

Question 10

function of desmosomes

Answer 10

adhesion and assure force transferred from cell to cell

Question 11

function of gap jucntion

Answer 11

low resistance path for electric current

Question 12

coupling between cardiac muscle cells is both ___ and ___

Answer 12

mechanical and electrical

Question 13

what is cardiac muscle made primarily of

Answer 13

myocytes in a collagen weave

Question 14

what does each cardiac myocyte contain?

Answer 14

contains multiple rod strands called myofibrils

Question 15

what are myofibrils composed of?

Answer 15

end to end array of sarcomere

Question 16

what is a sarcomere

Answer 16

contractile unit made of actin and myosin from Z to Z

Question 17

what is a myofiber

Answer 17

1 multinucelate muscle cell with all usual organelles + myofibrils

Question 18

what is in thin filament?

Answer 18

actin

Question 19

what is in thick filament

Answer 19

myosin

Question 20

what is a thin filament also known as

Answer 20

I band extending from Z line

Question 21

what is a thick filament also known as

Answer 21

A band-

Question 22

what is myosin made of?

Answer 22

2 heavy chains + 4 light chains (2 regul + 2 essential)

Question 23

what are the two forms of myosin?

Answer 23

alpha

beta

Question 24

which myosin isoform has higher ATPase activity? and which form is associated with heart failure?

Answer 24

higher ATPase = alpha

heart failure = beta

Question 25

what does actin bind on to?

Answer 25

tropomyosin | troponin

Question 26

what is troponin C structure

Answer 26

1 Ca2+ binding site | skeletal muscle has 2

Question 27

What is troponin I

Answer 27

has N-terminal extension with 2 PKA phosphorylation site interacts with Trop C but is released with phsophorylation

Question 28

what is troponin T

Answer 28

binds tropomyosin

Question 29

what is tropomyosin

Answer 29

only alpha isoform in heart

Question 30

Cross bridge cycle

Answer 30

1) Depol open plasma membrane Ca2+ channel 2) Ca2+ binds RyR2 on membrane of SR to induce more Ca2+ release 3) Ca2+ binds Trop C --> conformation change in tropomyosin to expose cross bridge sites on actin 4) ATP on myosin hydrolyzed to ADP + Pi 5) Actin interact with myosin --> crossbridge 6) muscle contract when ADP dissoc 7) Ca2+ released from troponin resets tropomyosin blocking actin 8) ATP rebinds myosin head --> reset

Question 31

4 state crossbridge cycle #1 Rest state

Answer 31

No Ca2+ weakly bound no force generate

Question 32

``` 4 state crossbridge cycle #2 transition state ```

Answer 32

Ca2+ bound cross bridge weak bound no force generate

Question 33

``` 4 state crossbridge cycle #3 active state ```

Answer 33

Ca2+ bound cross bridge strong bound force generate

Question 34

``` 4 state crossbridge cycle #4 active state ```

Answer 34

No Ca2+ cross bridge strong bound force generate

Question 35

How is cross bridge cycling regulated?

Answer 35

Via calcium flow (level of calcium determine whether cross bridge forms)

Question 36

Sliding filament hypothesis how does thin filament change?

Answer 36

NO CHANGE IN LENGTH BTWN CONTRACT AND RELAX STATE

Question 37

Sliding Filament hypothesis how does thick filament change

Answer 37

NO CHANGE IN LENGTH LIKE THIN BUT DOES CHANGE ORIENTATION OF HEAD

Question 38

Function of Titin

Answer 38

allow interaction btwn myosin and actin to contract and relax without changing intracellular distance btwn actin/myosin diastolic propertis

Question 39

what are 2 diff titin isoforms? which is longer and less stiff?

Answer 39

``` N2b N2ba (longer and less stiff) ```

Question 40

which titin isoform is found in diastolic heart failure

Answer 40

incr N2b

Question 41

what is frank starling law of heart

Answer 41

1) MORE VOLUME OF BLOOD ENTER HEART IN DIASTOLE (EDV) | 2) MORE VOLUME BLOOD EJECT DURING SYSTOLE (SV)

Question 42

what is frank starling law of heart based on?

Answer 42

length tension relationship incr fiber length, incr force of contraction (tension)

Question 43

how does length tension relationship apply to heart?

Answer 43

incr preload incr fiber length incr force of contraction

Question 44

is there a limit on length tension relationship?

Answer 44

YES, OVERSTRETCH BEYOND OPTIMUM WILL DECREASE TENSION AND CONTRACTION

Question 45

what are the mechanisms behind length-tension relationship

Answer 45

1) extent of overlap 2) changes in sensitivity of myofilament to calcium 3) incr calcium release

Question 46

mechanisms behind length tension relationship extent of overlap

Answer 46

Change resting length of muscle --> proportional change in individual sarcomere Peak at 2.2-2.3 uM

Question 47

mechanisms behind length tension relationship change in sensitivity of myofilament to calcium what is main factor in myocardial contraction

Answer 47

1) calcium is main factor in myocardial contraction

Question 48

mechanisms behind length tension relationship change in sensitivity of myofilament to calcium what is aclacium sensitivity

Answer 48

responsiveness of myofilament to calcium

Question 49

mechanisms behind length tension relationship change in sensitivity of myofilament to calcium what are factors that regulate calcium sensitivity of myofilament

Answer 49

Troponin I phosphorylation Isoform composition sarcomere length