Muscle Contraction

Question 1

1st step?

Answer 1

When the muscle is stimulated, the action potential passes along the sarcolemma and down the t-tubules into the muscle fibres

Question 2

2nd step?

Answer 2

The action potential is carried to the sarcoplasmic reticulum which stores Ca2+ ions- the Ca2+ ions diffuse into the myofibrils

Question 3

3rd step?

Answer 3

The Ca2+ ions bind to troponin which is attached to tropomyosin.
Troponin changes shape which causes tropomyosin to move aside from myosin binding sites on actin filaments
This exposes the binding sites on the actin filaments for the myosin heads.

Question 4

4th step?

Answer 4

Myosin heads bind to the actin- forming actin-myosin cross bridges

Question 5

5th step?

Answer 5

Actin filaments are pulled inwards, over the myosin filaments- power stroke

Question 6

Step 6?

Answer 6

An ATP molecule binds to the myosin head- causing the actin-myosin cross bridge to break and the myosin head detaches from the actin

Question 7

Step 7?

Answer 7

ATP is hydrolysed into ADP and Pi, releasing energy, which resets the myosin head so it can then bend again further up the actin filament- forming another actin myosin cross bridge