Choose the correct properties of muscle fibres.
$I.$ Muscle fibre is lined by the plasma membrane called sarcolemma.
$II.$ Cytoplasm of the muscle fibre is called tonoplasm.
$III.$ Sarcolemma of the muscle fibre encloses the sarcoplasm.
$IV.$ Muscle fibre is a syncytium.
Select the correct option.

Short duration contractions are characteristic of:

Given below are two statements $:-$
Statement-$I$ :- Each organised skeletal muscle in human body is made of a number of fascicles,held together by a common connective tissue layer called fascia.
Statement-$II$ :- The portion of the myofibril between two successive '$Z$' lines is considered as the functional unit of muscle contraction,known as a sarcomere.
In the light of the above statements,choose the correct answer from the options given below $:-$

Myoglobin is found in

Striated and voluntary muscle fibres are found in

When we lift a heavy object,what happens to the muscles of the arm?