Glucose is produced by breaking down glycogen stored in cells. Glucose is used in all respiration and produces ATP. ATP provides energy for muscle contraction.

Movement of any part of the body requires the combined effect of two muscles. The two muscles work in opposite ways. One of the muscles is called antagonistic muscle of the other. These are called antagonistic muscle pairs.

This muscle contracts and expands the heart to maintain normal blood flow. Cardiac muscle contains functional syncytium. That is, when one cell shrinks, other cells shrink.

This muscle is found only in the wall of the heart. The muscle of the heart is called the myocardium. Myocardium has two layers. Epicardium and Endocardium. The outer layer is called epicardium and the inner layer is called endocardium.

Cardiac cells appear long, cylindrical and branched. Its length is 0.8 mm and diameter is 12-15 micrometers.
1. Sarcolemma: It is covered by a membrane called sarcolemma.
2. Sarcoplasm: Cytoplasm of muscle is called sarcoplasm. It contains mitochondria.
3. Nucleus: In the center of every cell is a nucleus. It performs biological functions of cells.
4. Myofibrils: Myofibril fibers run along the length of the cell. Myofibrils have striated spots.
5. Intercalated disc: Two adjacent sarcolemmas fuse to form a disc. One is called an intercalated disc. It is one of the identifying features of heart muscle.

The muscle that forms the wall of the heart is called cardiac muscle. It is a type of involuntary muscle. Between the heart muscles are the connective tissue of the areola. It never gets bored.

1. The contraction-expansion capacity of this muscle is slow and long-lasting.
2. It regulates the rhythmic activity of the organs.
3. It controls the movement of food material in the process of peristalsis.
4. Controls the contraction and expansion of blood vessels, airways, excretory canals etc.

It is located in alimentary canal, blood vessel, trachea, urinary tract, uterus etc.

Involuntary muscles are squash-shaped in appearance. That is, it is wide in the middle and narrow at both ends. Its length is 15-200 micrometers and diameter is 8-10 micrometers.
1. Sarcolemma: The muscle sheath is called sarcolemma. The sarcolemma is indistinct in involuntary muscles.
2. Sarcoplasm: Cytoplasm of muscle is called sarcoplasm. Cytoplasm contains mitochondria. Its cytoplasm is called sarcoplasm. Each cell has a nucleus and numerous fibers called myofibrils.
3. Nucleus: Each muscle cell has a nucleus. It performs biological functions of cells.
4. Myofibril: Myofibril fibers are present along the length of the cell. Myofibril fibers are composed of actin and myosin filaments. Actin and myosin filaments together are called sarcomere.

Muscles whose actions are not controlled by the will of the animal are called involuntary muscles. They are also called visceral muscles because they are present in the walls of various organs (vessels).