Which fibres,contractile in nature,are found in muscles?

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.

During muscle contraction:

Stimulation of a muscle fiber by a motor neuron occurs at

Discuss the difference between red muscle and white muscles.

$A$ collagenous connective tissue layer holds the muscle bundles together.