Question

Which of the following changes Occurs when a skeletal muscle contracts?

• A. A bands shorten
• B. I bands shorten
• C. Z lines slide farther apart
• D. Actin filaments contract

Answer 1

The correct option is B I bands shorten

• The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin.
  
• ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.

• Myofibril activity is required for muscle contraction on the molecular level.
  
• When ATP binds to myosin, it separates from the actin of the myofibril, which causes a contraction.
• H zone disappears and Z zone moves towards each other and I band shortens.
• The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin.
• ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.
• So, the correct option is 'I bands shorten.'.