Where are calcium ions stored in muscle cells?

Contractile tissues have the following features:
$(i)$ Mesodermal in origin
$(ii)$ They contain stretch receptors
$(iii)$ Rhythmic contractions are seen in them
$(iv)$ They do not fatigue during the life of the animal
Which of the above are characteristics of sphincters?

Name the connective tissue sheath which surrounds the muscle bundles.

How is the meromyosin formed?

In the thin filament of skeletal muscle fibre,a small globular protein that masks the active sites for myosin on the $F-$actin,is

Which one of the following takes place in a myofibril when skeletal muscle contracts?
$A$-band (Dark band) | $I$-band (Light band) | $H$-zone