In a muscle fiber,$Ca^{++}$ is stored in the .....

Consider the following four statements $(a-d)$ and select the option which includes all the incorrect ones:
$(a)$ Skeletal muscle fibre is a syncytium as the sarcoplasm contains many nuclei.
$(b)$ In the centre of each $I$-band is an elastic fibre called $H$-line which bisects it.
$(c)$ In the resting state,a subunit of troponin masks the active binding sites for myosin on the actin filaments.
$(d)$ The contraction of a muscle fibre takes place by the sliding of the thick filaments over the thin filaments.

Which contractile protein of skeletal muscle is associated with $ATPase$ activity?

Which ions must be present for the binding of cross-bridges during muscle contraction?

Black bands of myofibrils are known as

The dark bands ($A$-bands) of a skeletal muscle are known as