Sliding Filament Theory

Question 1

Describe resting phase

Answer 1

• No action potential
• Ca2+ available
• No bind bt/w actin + myosin

Question 2

Describe exciation phase

Answer 2

1. Impulse reaches neuromuscular junction/motor end plate
2. Causes acetylcholine released across synaptic cleft
3. Creates nervous stimulation of muscle tissue + triggers action potential

Action potential is created

Question 3

Describe contraction phase

Answer 3

1. Action potential causes Ca2+ released, which binds to troponin - causes tropomyosin to be moved away (exposes binding sites on actin filament)
2. If ATP present, cross bridge forms (myosin head attaches exposed binding site of actin.
3. Myosin heads ‘pull’ on actin filament (power stroke) with ratchet like mechanism pulls the Z lines on sacromere toward M line + sacromere shortens

Muscles are shortening due to the above

Question 4

Describe recharge phase

Answer 4

• If binding site available for myosin further along actin filament
• ATP + Ca2+ available

Contraction stage repeats if the above

Question 5

Describe relaxation phase

Answer 5

• No Ca2+ available
• No bond bt/w actin + myosin (returns to rest)