Sliding filament model/stages of contraction

Question 1

1st stage?

Answer 1

Resting state, muscle is relaxed

Question 2

2nd stage?

Answer 2

Nerve impulse depolarises the sarcolemma of the muscle fibre

Question 3

3rd stage?

Answer 3

Transverse tubules transmit this depolarisation throughout the fibre

Question 4

4th stage?

Answer 4

Calcium ions enter the myofibril from the sarcoplasmic reticulum

Question 5

5th stage?

Answer 5

The calcium ions bind to the troponin, changes its shape, dragging the tropomyosin away from the myosin binding sites of the actin

Question 6

6th stage?

Answer 6

The myosin heads bind to the myosin-binding sites that have just been exposed

Question 7

7th stage?

Answer 7

ADP and inorganic phosphate in the myosin head are released which causes the myosis head to bend, pulling on the actin (moving it towards the sarcomere)

Question 8

8th stage?

Answer 8

Fresh ATP binds to the myosin head, causing the actin to release it

Question 9

9th stage?

Answer 9

The myosin head acts as an ATPase enzyme hydrolysing the ATP into ADP and inorganic phosphate - extends the head into a position next to the next myosin-binding site