Myocyte contraction coupling

Question 1

Describe the structure of the cardiac muscle? (3)

Answer 1

Intercalated disks made of

Mechanical links – desmosomes (filaments)

Electrical links – gap junctions

Question 2

What are the 3 channels that regulate Ca2+ and cardiac relaxation in the mitochondria? (3)

Answer 2

NCX1
PMCA
SETCA2

Question 3

What is the strength / velocity of contraction in myocyte determined by? (2)

Answer 3

-How much Ca2+ increases
-Sensitivity contractile proteins to Ca2+

Question 4

What is the strength / velocity of contraction in myocyte determined by? (2)

Answer 4

-Pre-load - how much blood is in ventricles before they contract
-Afterload - what pressure is ventricle against to pump out blood from heart

Question 5

What connects sarcomeres together?

Answer 5

Desmin

(set length to get certain amount of contraction)

Question 6

What two proteins are important for generating passive tension?

Answer 6

-Titin
-Desmin

Question 7

What do Titian and Desmin do? (2)

Answer 7

Titin links through z line to myosin, different version with different lengths, length determines how much contraction is generated

Desmin links sarcomeres together, in cardiac muscle there is 5x more desmin than skeletal muscle

Question 8

How do you have the highest number of cross bridges between actin and myosin?

Answer 8

Optimum sarcomere length

Question 9

What effect does sarcomere length have in skeletal muscle?

Answer 9

As sarcomere length increases tension decreases

Question 10

What kind of length of sarcomere is required for activation in cardiac muscle?

Answer 10

Short length

Question 11

Why does a longer length of cardiac muscle mean less cross-bridges between actin and myosin?

Answer 11

If you stretch muscle further, you reduce the amount of overlap between actin and myosin, number of cross-bridges formed is reduced

Question 12

What happens when cardiac muscles are stretched? (4)

Answer 12

-Actin and myosin closer together
-Increases chances of cross-bridges formed
-Increase in passive tension
-Activates stretch mediated calcium channels

Question 13

What kind of tension is in systole and diastole? (2)

Answer 13

Diastole = passive tension

Systole = active tension

Question 14

What does long sarcomere length mean?

Answer 14

More passive tension

Question 15

How can you calculate velocity of shortening?

Answer 15

-Muscle with adjustable stop and weight for after load while it is isovolmetric

-You set tension, then you can remove stop and muscle shortens

Question 16

How does velocity of shortening change at high and low arteriole pressures? (2)

Answer 16

-High arteriole pressure velocity of shortening reduced
-Low arteriole pressure velocity of shortening increased

Question 17

How does preload effect velocity of shortening and tension? (2)

Answer 17

-Higher pre-load velocity of shortening is faster
-Higher pre-load means more tension generated

Question 18

What string and speed of contraction do these have? (8)

Large volume & low arterial pressure -
Large volume & high arterial pressure -
Low volume & low arterial pressure -
Low volume & high arterial pressure -

Answer 18

Large volume & low arterial pressure - strong contraction, fast contraction
Large volume & high arterial pressure - strong contraction, slow contraction
Low volume & low arterial pressure - weaker contraction, fast contraction
Low volume & high arterial pressure - weaker contraction, slow contraction

Question 19

What do inotropic agents and chronotropic agents change?

Answer 19

Contractility - inotropic
Rate - chronotropic

Question 20

What does increase in heart rate mean in terms of tension and Ca2+ availability? (2)

Answer 20

Increase in heart rate means increase in tension and Ca2+ availability

Question 21

What does reversal of NCX in muscle mean?

Answer 21

Reversal of NCX means it take sodium out and calcium in rather than the normal way round