Question

a&p flix activity: the cross bridge cycle 2 parts -- of 1 point the cross bridge cycle starts when ________. select the best answer. ca²⁺ from the sarcoplasmic reticulum binds to tropomyosin ca²⁺ is actively transported into the sarcoplasmic reticulum atp binds to troponin and is hydrolyzed to adp and pᵢ acetylcholine diffuses away from the synaptic cleft ca²⁺ from the sarcoplasmic reticulum binds to troponin

Explanation:

The cross - bridge cycle in muscle contraction begins when calcium ions ($Ca^{2+}$) released from the sarcoplasmic reticulum bind to troponin. This binding causes a conformational change in the troponin - tropomyosin complex, exposing the myosin - binding sites on actin.

Answer:

E. $Ca^{2+}$ from the sarcoplasmic reticulum binds to troponin