Question

Which of the following occurs during the contraction phase?

A. Acetylcholine binds to the sarcolemma
B. Ca²⁺ release from the sarcoplasmic reticulum is blocked
C. Cross-bridge cycling is taking place
D. The sarcomeres are increasing in length

Answer 1

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.