cardiac muscle structures 3 Flashcards Preview

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Flashcards in cardiac muscle structures 3 Deck (31):
1

titin

1. allows the sarcomere to change
2. the major protein allowing for movement
3. acts like an elastic spring
4. One of the major proteins responsible for passive elastic properties of the cell (and thus for diastolic properties of the heart)

2

titin isoforms

1. N2B
2. N2BA

3

N2B

more rigid, increases stiffness
can be short term phosphorylated

4

N2BA

less rigid
decreases stiffness

5

Titin regulation sites

there are a ton of them

6

steps of muscle contraction

1. Action potential leads to calcium release.
2. Calcium binds to troponin C.
3. Troponin complex undergoes structural change, moving tropomyosin out of the way.
4. Myosin binds actin and crossbridge moves.
5. Calcium is released, tropomyosin reblocks binding site - relaxation

7

Frank-Starling Law of the Heart

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.

8

The Frank-Starling law of the heart describes the effect of .

increasing preload on the force of contraction.

the greater the volume of blood entering the heart during diastole, the greater the volume of blood ejected during contraction.

9

the frank starling law is due to

thelength-tension relationship described – as we increase the fiber length, the force of contraction for a given stimulus is increased

10

When cardiac muscle is stimulated to contract at low resting lengths, the amount of active tension developed is ____.

small

11

When you increase the muscle length, the active tension developed ____

dramatically increases.

12

Frank-Starling’s law of the heart: myofilament length-dependent activation

“The Greater the Preload, the greater the force generated”

13

Mechanisms behind the length-tension relationship

1. extent of the overlap
2. change in the sensitivity of the myofilament to calcium
3. increased calcium release

14

Extent of overlap:

Histological studies indicate that the changes in the resting length of the whole muscle are associated with proportional changes in the individual sarcomere. Peak tension development occurs at sarcomere lengths of 2.2 to 2.3 mM.

15

Change in the sensitivity of the myofilament to calcium:

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”.

16

Increased calcium release:

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

17

Calcium Sensitivity of Cardiac Muscle

1. Calcium is the central factor in myocardial contraction
2. The responsiveness of the myofilament to calcium is “calcium sensitivity”

18

factors that regulate calcium sensitivity of the myofilament

1. TnI phosphorylation
2. Isoform composition
3. sarcomere length

19

afterload

the pressure that ventricle has to generate in order to eject blood out of the chamber – most closely related to aortic pressure (except with disease)

20

what changes the velocity on the sarcomeric level?

1. Phosphorylation of MLC
2. Phosphorylation of MyBPC

21

THE LAW OF LAPLACE

T = P x r/h

22

Excitation of cardiac myocytes initiates contraction by

increasing the cytosolic calcium that activates the contractile proteins by binding to troponin, moving tropomyosin and allowing myosin binding to actin.

23

The mechanical response of the myocyte depends on

1. preload
2. afterload
3. the contractility of the myofilament

24

preload

the initial length of the myocyte

25

afterload

the tension that needs to be developed

26

the contractility of the myofilament is determined mainly by

calcium sensitivity

27

The cardiac myocyte length-tension relationships are correlated with

changes in pressure-volume in the intact ventricle.

28

Changes (both translationally and post-translationally) of the myofilament proteins are associated with

cardiac dysfunction

29

Proteomic regulation of crossbridge cycling underlies:

changes in contraction/relaxation of the heart with exercise, age, disease, etc

30

Thin and thick filaments contain

regulatory proteins that are modifiable

31

Titin largely determines the

passive elastic properties of the heart (i.e. diastolic properties)