The largest muscle in the human body is . . . . . . .

Assertion: Fatigue is the inability of a muscle to relax.
Reason: It is due to lactic acid accumulation by repeated contractions.

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 $:-$

Cardiac muscle fibres are

Sarcolemma,sarcoplasm,and sarcoplasmic reticulum refer to a particular type of cell in our body. Which is this cell and to what parts of that cell do these names refer to?

Describe the mechanism of muscle contraction with a diagram.