C-Cardiac Muscle Myocyte Structure & Function Flashcards Preview

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Flashcards in C-Cardiac Muscle Myocyte Structure & Function Deck (53):
1

Regulators of Cardiac Output

preload
afterload
contractility

CO= Heart Rate x Stroke Volume

2

Afterload is

pressure ventricles are pushing against to eject blood from the heart

3

Preload is

volume in the heart (ventricle) before it beats

4

Heart is made up of approximately 2 -3 billion _________ but this accounts for only about 1/3 of the number of cells

cardiac muscle cells

responsible for corrdinated contraction

5

Other cell types include fibroblasts, endothelial cells, smooth muscle cells, and immune cells in the

heart

6

Contraction starts at

the apex ofthe heart

7

Other cell types include ___________ in the heart

fibroblasts
endothelial cells
smooth muscle cells
immune cells

8

Fibrillar collagen type I and III are the most predominant components of the ECM and disruptions in the ECM occur with disease and___________

cardiac remodeling

9

Cardiac muscles are __________ (like skeletal muscle)

striated

10

Cardiac muscles are ___________ direct neural control (unlike skeletal)

NOT under

11

Cardiac muscle cells are shorter, narrower & richer in mitochondria than skeletal muscle cells have __________ nucleus

only one or two

12

__________ activity of myosin is slower in cardiac than skeletal but faster than smooth muscle

ATPase

13

Cardiac muscle cells are connected with each other through_________-

intercalated discs

(Coincide with the Z discs; contain desmosomes and gap junctions)

14

Ca2+ binding to troponin regulates __________ interaction

actomyosin

15

coupling between cardiac muscle cells is both___________

mechanical and electrical

16

Desmosomes provide adhesion and assure that the ______ generated in one cell passes to the other (connects to ECM)

force

17

Ca2+ binding to ________ regulates actomyosin interaction

troponin

18

_________ provide low resistance pathways for electrical current

Gap junctions

19

_______ binding to troponin regulates actomyosin interaction

Ca2+

20

Composed of hundreds of long, contractile myosin molecules arranged in a staggered side by side complex

Thick Filament

21

Composed of hundreds of long, contractile myosin molecules arranged in a staggered side by side complex

Thin Filament

22

The unit of contractile activity composed mainly of actin and myosin and extending from Z line to Z line in a myofibril

Sarcomere

23

End-to-end arrays of identical sarcomeres

Myofibril

24

A single multinucleate muscle cell containing all the usual cell organelles plus many myofibrils

Myofiber

25

Composed of two heavy chains and four light chains, ATPase activity (a vs b)

motor proteins that move along actin filaments, while hydrolyzing ATP.

Myosin

26

Similar to skeletal muscle myosin
Binds tropomyosin and troponin

Actin

27

A dumbbell shaped protein with the N-lobe containing only ONE Ca2+-binding site (unlike skeletal which contains two)

Troponin C (TN-C)

28

Contains a unique N-terminal extension of 32 amino acids that contains 2 PKA phosphorylation sites critical for adrenergic responsiveness of the heart.

Troponin I (TN-I)*****

-extension interacts with TN-C but is released with phosphorylation.

29

Binds tropomyosin. Developmental regulation of isoform expression (and perhaps pathological regulation).

Troponin T (TN-T)

30

Only alpha isoform in the heart (but may be pathologically regulated)

Tropomyosin

31

Troponin i

lies over myosin binding site
inhibitor

phosphorylation sites critical for adrenergic responsiveness of the heart.

interacts with TN-C but is released with phosphorylation.

32

AP leads to Ca release.
Ca binds to troponin C.
Troponin complex undergoes structural change, moving tropomyosin out of the way.
Myosin binds actin and crossbridge moves.
Ca is released, tropomyosin reblocks binding site - relaxation
****

Contraction – Relaxation Cycle

33

Contraction – Relaxation Cycle****

AP leads to Ca release.

Ca binds to troponin C.

Troponin complex undergoes structural change, moving tropomyosin out of the way.

Myosin binds actin and crossbridge moves.

Ca is released, tropomyosin reblocks binding site - relaxation

34

Cross bridge

myosin head attached/binding to actin
ultimately generates force

35

“rest” state (state 1) during diastole

Cross bridges are initially in a weakly bound, non-force-generating “rest” state

36

The triggering of force generation and contraction is governed by Ca2+ fluxes determined by the dynamics of electrochemical coupling of Ca2+ release and Ca2+ binding to ________

cTnC.

Cross bridges and thin filaments now enter into a transition state (state 2)

37

CO =

heart rate x stroke volume.

38

actin (thin) filaments of muscle fibres slide past the myosin (thick) filaments during muscle contraction, while at constant length.

Sliding Filament Hypothesis

39

Titin forms an ________, and there are many points of regulation within titin


elastic spring

major protein in cardiac muscle cell

40

also known as connectin, is a flexible intrasarcomeric filamentous protein, which is largest proteins known today.

titin

41

Action potential leads ______ in the heart .

to ca release

42

Calcium binds to ________ in the heart.

troponin C

43

Troponin complex undergoes structural change, moving _______ out of the way.

tropomyosin

44

Myosin binds _______ and crossbridge moves.

actin

45

Calcium is released, __________ reblocks binding site - relaxation

tropomyosin

46

The effect of increasing preload on force of contraction:

the greater the volume of blood entering the heart during diastole (end-diastolic volume), the greater the volume of blood ejected during systolic contraction (stroke volume) and vice versa.

Frank-Starling Law of the Heart

47

Frank-Starling Law of the Heart

The Greater the Preload, the greater the force generated”

with a Length-tension relationship for the myocytes

48

Mechanisms behind the length-tension relationship

Extent of overlap
Change in the sensitivity of the myofilament to calcium:
Increased calcium release

49

At short lengths only a fraction of the potential cross-bridges are activated by a given increase in calcium.

At longer lengths, more of the cross-bridges become activated by the same change in intracellular calcium. No time delay in the “sensor”.

Change in the sensitivity of the myofilament to calcium

50

Occurs several minutes after changing the length of the muscle. May be due to stretch-sensitive ion channels in the cell membrane.

Increased calcium release

51

Calcium Sensitivity of Cardiac Muscle

Several factors regulate calcium sensitivity of the myofilament

Several factors regulate calcium sensitivity of the myofilament
TnI phosphorylation
Isoform composition
sarcomere length

52

The responsiveness of the myofilament to calcium is___________

“calcium sensitivity”

53

_________ is the central factor in myocardial contraction

Calcium