Unstriped muscles are found in

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?

The contraction of muscle of shortest duration is seen in

The refractory period of a muscle fibre in mammals is:

Contraction of a muscle is caused by

'Gastrocnemius' is a muscle of