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

1.	transverse tubule system	2.	sarcoplasmic reticulum
3.	myofibrils	4.	terminal cisternae

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.

Cylindrical, branched muscle cells that are arranged into functional syncytium are:
1. cardiac muscles.
2. skeletal muscles.
3. single unit smooth muscles.
4. multi unit smooth muscles.

A muscle cell is called as a:

All the following are parts of the actin myofilament in a sarcomere except:
1. actin
2. cisternae
3. tropomyosin
4. troponin