Question

The cross bridges of sarcomere in skeletal muscle are made up of
A. Actin
B. Myosin
C. Troponin
D. Tropomyosin

Answer 1

Hint: The movement of the muscle fibres is described by the cross bridge theory the protein of the muscle forms a bridge like structure for the movement. The protein that helps in the formation of that bridge has a round head.

Complete Answer:
- Actin :- Actin is one of the important proteins in the muscle fibres. The actin protein filaments are also known as the thin filament of the muscle, it provides space for the attachment of the myosin protein to it for the contraction of the sarcomere.
- Myosin :- Myosin is also known as the thick filament of the muscle fibre. The site where myosin attached is present on the actin filament but it is occupy by the troponin unit, at the time of the contraction the concentration of $ca^{++}$ ions increases inside the muscle cell and this $ca^{++}$ ion get attach on the troponin so that myosin attached on the actin protein and forms the cross bridge for contraction.
- Troponin:- The function of troponin is just to occupy the active site of myosin protein in the actin protein during the resting stage of the muscle.
- Tropomyosin :- It is also an important protein in the contraction process of the smooth muscles. It plays an important role in the contraction of the smooth muscle in the body.
So from the above details we can say that the protein which helps in the formation of cross bridges in the sarcomere is myosin protein.

Hence the option B is correct.

Note: The muscle cells are also known as sarcomere and the endoplasmic reticulum of the muscle cell is known as sarcoplasmic reticulum. During contraction the contraction of $ca^{++}$ was increased by sarcoplasmic reticulum.