Muscle Contraction

Question 1

6 steps of contraction initiation.

Answer 1

1) Action potential on nerve
2) Action potential on sarcolemma
3) Action potential in t-tubules
4) Release Ca++ from SR
5) Ca++ binds troponin (at end of tropomyosin)
6) Tropomyosin moves off active sites on actin

Myosin head is then able to bind

Question 2

6 steps of active contraction.

Answer 2

1) Actin + myosin –> actomyosin cross bridge
2) Spontaneous configuration change
3) PO4 and ADP released
4) ATP attached to myosin (breaking actomyosin cross bridge)
5) ATP hydrolyzed - myosin head reset
6) New actomyosin crossbridge

Question 3

4 steps of contraction termination (relaxation).

Answer 3

1) Sarcolemma and SR depolarized (ATP)
2) Ca++ pumped back into SR (ATP)
3) Troponin releases tropomyosin (covers active site)
4) Actomyosin + ATP –> actin + myosin (breaks cross bridge so it cannot reform)

Question 4

What is the role of sarcoplasmic reticulum in muscle contraction?

Answer 4

• Ca++ storage - relaxed muscle

- Ca++ release - initiate contraction

Question 5

What is the role of ATP in muscle contraction?

Answer 5

• Relaxing factor
• Break actomyosin x-bridge
• Energy for resetting myosin bridge
• Energy for Ca++ pump
• Energy for Na/K pump (depolarization of membranes