cardiac muscle structures 3

Question 1

titin

Answer 1

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)

Question 2

titin isoforms

Answer 2

1. N2B

2. N2BA

Question 3

N2B

Answer 3

more rigid, increases stiffness

can be short term phosphorylated

Question 4

N2BA

Answer 4

less rigid

decreases stiffness

Question 5

Titin regulation sites

Answer 5

there are a ton of them

Question 6

steps of muscle contraction

Answer 6

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

Question 7

Frank-Starling Law of the Heart

Answer 7

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.

Question 8

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

Answer 8

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.

Question 9

the frank starling law is due to

Answer 9

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

Question 10

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

Answer 10

small

Question 11

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

Answer 11

dramatically increases.

Question 12

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

Answer 12

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

Question 13

Mechanisms behind the length-tension relationship

Answer 13

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

Question 14

Extent of overlap:

Answer 14

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.

Question 15

Change in the sensitivity of the myofilament to calcium:

Answer 15

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”.

Question 16

Increased calcium release:

Answer 16

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

Question 17

Calcium Sensitivity of Cardiac Muscle

Answer 17

1. Calcium is the central factor in myocardial contraction

2. The responsiveness of the myofilament to calcium is “calcium sensitivity”

Question 18

factors that regulate calcium sensitivity of the myofilament

Answer 18

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

Question 19

afterload

Answer 19

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)

Question 20

what changes the velocity on the sarcomeric level?

Answer 20

1. Phosphorylation of MLC

2. Phosphorylation of MyBPC

Question 21

THE LAW OF LAPLACE

Answer 21

T = P x r/h

Question 22

Excitation of cardiac myocytes initiates contraction by

Answer 22

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

Question 23

The mechanical response of the myocyte depends on

Answer 23

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

Question 24

preload

Answer 24

the initial length of the myocyte

Question 25

afterload

Answer 25

the tension that needs to be developed

Question 26

the contractility of the myofilament is determined mainly by

Answer 26

calcium sensitivity

Question 27

The cardiac myocyte length-tension relationships are correlated with

Answer 27

changes in pressure-volume in the intact ventricle.

Question 28

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

Answer 28

cardiac dysfunction

Question 29

Proteomic regulation of crossbridge cycling underlies:

Answer 29

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

Question 30

Thin and thick filaments contain

Answer 30

regulatory proteins that are modifiable

Question 31

Titin largely determines the

Answer 31

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