Final answer:
During the contraction phase, ACh binds to the sarcolemma, Ca²⁺ is released from the sarcoplasmic reticulum, and cross-bridge cycling takes place.
Step-by-step explanation:
The contraction phase of muscle contraction involves several events. First, acetylcholine (ACh) binds to the sarcolemma, triggering depolarization. This leads to an action potential that travels along the sarcolemma and T-tubules, eventually reaching the sarcoplasmic reticulum (SR).
Next, Ca²⁺ is released from the SR. The binding of Ca²⁺ to troponin initiates a conformational change, exposing the actin-binding sites and allowing for cross-bridge cycling between actin and myosin.
During cross-bridge cycling, the myosin heads bind to actin, undergo a power stroke to slide the thin filaments, and then detach and reset for another cycle. This cycling generates force and leads to muscle contraction.