Describe cross bridge movement during muscle contraction. Begin with action potential in the muscle and end with relaxation. What happens if ATP is not available

Answer 1

Answer:

1. Action potential travels along axon membrane to a neuromuscular junction
2. Ca2+ channels open and Ca2+ enters the presynaptic terminal
3. Acetylcholine is released from presynaptic vesicles
4. Acetylcholine stimulates Na+ channels on the postsynaptic membrane to open
5. Na+ diffuses into the muscle fibre, initiating an action potential that travels along the sarcolemma and T-tubule membranes
6. Action potentials in the T-tubule cause the sarcoplasmic reticulum to release Ca2+
7. On the actin, Ca2+ binds to troponin which moves tropomyosin and exposes myosin attachment sites
8. ATP molecules are broken down to ADP and P, which releases energy needed to move the myosin heads (The release of ADP+P triggers the 'power-stroke' of the myosin heads on the actin filaments, pulling towards the center of the sarcomere = contraction)
9. ATP binding to myosin head group, returns the head group to relaxed position and releases it from actin and cycle can continue as long as Ca2+ remains present.