In the myofibrils of muscle fibre:

The dark bands in a myofibril are due to the presence of:

Analogy type questions:
$(1)$ The portion between two successive $Z$-lines is the functional unit of contraction,which is called the sarcoplasmic reticulum / sarcomere.
$(2)$ The thick filaments in the $A$-band are held together in the middle of this band by a thin fibrous membrane. It is called the $Z$-line / $M$-line.

Which of the following represents the correct matching of a body part and the muscle associated with its movement?

$ATP$ binding site is located on the

Cardiac muscle fibers differ from skeletal muscle fibers in that they are -