The correct statement regarding myofibril would be:

1.	It is the name for a muscle cell.
2.	It contains sarcoplasmic reticulum.
3.	It is made up of many sarcomeres.
4.	It is a bundle of muscle cells.

Myosin myofilaments are

1. made up of thick and thin myofilaments.

2. found only in the H zone.

3. not seen in the H zone.

4. attached to filaments that form the M line.

Identify the correct statement:

1. Tropomyosin is found in two forms – monomeric G and polymeric F.

2. The head of the myosin molecule binds to an active site on G actin.

3. ATPase is present in troponin A.

4. Actin molecules do not move during muscle contraction.

The extensions of the cell membrane that penetrate into the centre of skeletal and cardiac muscle cells are called as:

Arrange the following events in correct chronological order:

Acetylcholinesterase:

1. helps in binding of acetylcholine to its receptors.

2. catalyzes the synthesis of acetylcholine from acetate and choline.

3. stimulates receptors within the postsynaptic membrane.

4. breaks down acetylcholine.

Arrange the following events in the correct chronological order:

Study the events given below. Identify the set given in the choice that has the events in correct chronological order of their occurrence:

a. Ca²⁺ combines with tropomyosin
b. Ca²⁺ combines with troponin
c. tropomyosin pulls away from actin
d. troponin pulls away from actin
e. tropomyosin pulls away from myosin
f. troponin pulls away from myosin
g. myosin binds to actin

The majority of the muscle fibers in the skeletal muscles of the leg of a long distance runner is expected to have:
1. adaptation for sudden outburst of activity
2. primarily anaerobic source of energy
3. numerous mitochondria
4. large deposits of glycogen

During relaxation in smooth muscle:

1. calcium is removed from troponin.

2. ${\mathrm{Ca}}^{2+}$ bind to calmodulin.

3. myosin phosphatase removes phosphate from myosin.

4. Calcium is released from the sarcoplasmic reticulum.