Question

the active sites to which cross - bridges attach are found on the:
a t tubules
b actin myofilaments
c sarcoplasmic reticulum
d myosin myofilaments
e z disks

Explanation:

• T tubules: Transmit electrical impulses, not for cross - bridge attachment.
• Actin myofilaments: Have active sites. Myosin cross - bridges (from myosin myofilaments) bind to these active sites during muscle contraction.
• Sarcoplasmic reticulum: Stores and releases calcium ions, not for cross - bridge binding.
• Myosin myofilaments: Contain cross - bridges (not the sites where cross - bridges attach).
• Z disks: Mark the boundaries of sarcomeres, not related to cross - bridge attachment sites.

Answer:

B. actin myofilaments