The steps of excitation, excitation contraction coupling, contraction and relaxation in order

1️⃣ Excitation (Neuromuscular Junction)

→ Nerve impulse → ACh release → ACh binds receptor → Na⁺ influx → Muscle AP

2️⃣ Excitation–Contraction Coupling

→ AP travels down T-tubules → SR releases Ca²⁺ → Ca²⁺ binds troponin → Binding sites exposed

3️⃣ Contraction (Cross-Bridge Cycle)

→ Myosin binds actin → Power stroke → Detach (ATP) → Reset (ATP hydrolysis) → Repeat

4️⃣ Relaxation

→ No ACh → Ca²⁺ reuptake → Tropomyosin covers sites → Cross-bridges stop → Muscle returns to re