Page 24

Question 1

A patient with leg in cast for 2 weeks shows decreased gastrocnemius muscle size. Cause?

Answer 1

Temporary decrease of actin and myosin

Question 2

Largest molecular weight protein in muscle?

Answer 2

Myosin

Question 3

Portion of sarcomere that does not change during contraction?

Answer 3

A band

Question 4

What shortens during muscle contraction?

Answer 4

I band and H zone

Question 5

Cross-bridges in sarcomere are formed by?

Answer 5

Myosin

Question 6

During full skeletal muscle contraction what happens to Z discs?

Answer 6

Two Z discs touches the edges
of myosin filaments

Question 7

Actin binds to Z line via?

Answer 7

Actinin

Question 8

Cross-section through H-zone of relaxed sarcomere shows?

Answer 8

Thick filaments only

Question 9

Protein important in power stroke of skeletal muscle?

Answer 9

Myosin

Question 10

What covers actin binding sites at rest?

Answer 10

Tropomyosin

Question 11

Cause of rigor mortis or stiffness in dead body?

Answer 11

Failure of separation of myosin cross bridges

Question 12

Condition essential for initiating skeletal muscle contraction?

Answer 12

Membrane depolarization

Question 13

Skeletal muscle action potential requires which neurotransmitter?

Answer 13

Acetylcholine

Question 14

Calcium in skeletal muscle binds to which protein for contraction?

Answer 14

Troponin-C

Question 15

During relaxation of skeletal muscle where does Ca²⁺ go?

Answer 15

Ca returns to ser

Question 16

Cardiac muscle contraction is associated with shortening of?

Answer 16

I band

Question 17

Steps in excitation-contraction coupling in skeletal muscle: Action potential initiation

Answer 17

Depolarization of muscle cell membrane and T-tubules

Question 18

Steps in excitation-contraction coupling in skeletal muscle: Ca2+ release

Answer 18

T-tubule depolarization triggers Ca2+ release from sarcoplasmic reticulum (SR)

Question 19

Steps in excitation-contraction coupling in skeletal muscle: Ca2+ binding

Answer 19

Ca2+ binds to troponin C

Question 20

Cross-bridge cycle: Myosin-actin binding

Answer 20

Myosin head binds to actin (ADP + Pi attached)

Question 21

Cross-bridge cycle: Power stroke

Answer 21

Myosin head pivots

Question 22

Cross-bridge cycle: Cross-bridge detachment

Answer 22

ATP binds to myosin

Question 23

Cross-bridge cycle: Myosin re-cocking

Answer 23

ATP hydrolyzed to ADP + Pi

Question 24

Cross-bridge cycle: Cycle repeats

Answer 24

Continues as long as Ca2+ is bound to troponin C

Question 25

Skeletal muscle relaxation

Answer 25

Ca2+ is re-accumulated by SR via SERCA; tropomyosin re-covers actin sites

Question 26

Contraction effect on A band

Answer 26

No change

Question 27

Contraction effect on I band and H zone

Answer 27

Shortens