Skeletal muscles

Question 1

What is the role of ATP in muscle contraction?

Answer 1

• Move actin filament when attached to myosin
• Used to break actin myosin cross-bridge
• Used to return calcium ions back into sarcoplasmic reticulum via active transport once muscle contraction has stopped

Question 2

How is muscle contraction stimulated (sliding filament theory) ?

Answer 2

1. An action potential reaches the neuromuscular junction which causes voltage-gated calcium ion channels to open.
2. This calcium ions to enter which release acetylcholine from the vesicles
3. Acetylcholine releases and diffuses across synaptic clef and binds to receptors on muscle cell membrane
4. This causes voltage gated sodium ion channels to open allowing Na+ to enter and depolarize the membrane.
5. The depolarisation goes into the T-tubules which triggers and to the sarcoplasmic reticulum where calcium ions are released into the cytoplasm.
6. Ca2+ bind to troponin causing tropomyosin to move which exposes the myosin-binding sites on the actin filaments.
7. Myosin heads bind to the exposed binding sites on actin forming cross-bridges. By using ATP the myosin heads perform a power stroke by pulling the actin filaments towards the centre of the sarcomere causing contraction.