1. Human movement is through these muscles.
2. Controls body organs through contraction and expansion.
3. Regulates body posture and muscle tension.
4. Regulates body temperature.

Optional muscles are located in the eyes, tongue, pharynx etc. of animals.

Muscle fibers are arranged in clusters. Each bundle is called a fasciculus. Each fasciculus is covered by perimycium. Many fasciculi join together to form large clusters. Each large cluster is covered by epimycium.

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. Myofibrils have two types of lines or bands. anisotropic band (A) and isotropic band (I). Darker bands are called anisotropic or A bands and lighter bands are isotropic or I bands.

It is a long and cylindrical muscle. Its length is 1-4 cm and diameter is 10-40 micrometers. It is also called muscle fiber because the cells look like fine fibers.
1. Sarcolemma: Muscle tissue is covered by a sheath called sarcolemma.
2. Sarcoplasm: Its cytoplasm is called sarcoplasm. Cytoplasm contains mitochondria. Because these cells require a lot of energy.
3. Nucleus: Multiple nuclei in each muscle cell. 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. Myofibrils have two types of lines or bands. anisotropic band (A) and isotropic band (I). Darker bands are called anisotropic or A bands and lighter bands are isotropic or I bands.
5. Transverse lines: Several transverse lines are seen in optional muscles. These lines are called linear muscles or marked muscles.
6. Fasciculus: Muscle fibers are arranged in clusters. Each bundle is called a fasciculus. Each fasciculus is covered by perimycium. Many fasciculi join together to form large clusters. Each large cluster is covered by epimycium.

It is a long and cylindrical muscle. Its length is 1-4 cm and diameter is 10-40 micrometers. It is also called muscle fiber because the cells look like fine fibers.
1. Sarcolemma: Muscle tissue is covered by a sheath called sarcolemma.
2. Sarcoplasm: Its cytoplasm is called sarcoplasm. Cytoplasm contains mitochondria. Because these cells require a lot of energy.
3. Nucleus: Multiple nuclei in each muscle cell. 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. Myofibrils have two types of lines or bands. anisotropic band (A) and isotropic band (I). Darker bands are called anisotropic or A bands and lighter bands are isotropic or I bands.
5. Transverse lines: Several transverse lines are seen in optional muscles. These lines are called linear muscles or marked muscles.
6. Fasciculus: Muscle fibers are arranged in clusters. Each bundle is called a fasciculus. Each fasciculus is covered by perimycium. Many fasciculi join together to form large clusters. Each large cluster is covered by epimycium.

Muscles whose functions are controlled by the will of the animal are called voluntary muscles. It is also called skeletal or linear or smooth or striated muscle. There are 656 voluntary muscles in the human body.

Muscles are divided into three groups based on function, location and structure. These are-
1. Optional or linear or smooth or skeletal muscle.
2. Involuntary or nonlinear or smooth or visceral muscle.
3. Heart muscle or cardiac muscle.

1. Originates from embryonic mesoderm.
2. It is capable of expansion and contraction.
3. It is made up of numerous fibers called myofibrils.
4. It is covered by a sheath called sarcolemma.
5. Sarcolemma contains sarcoplasm.
6. It contains 75% water.
7. Each cell has a distinct nucleus.
8. Intracellular spaces are filled with various proteins.

Muscle tissue, which is formed from embryonic mesoderm, is capable of contraction and expansion and is composed of numerous fibers. Muscles are formed by the process of myogenesis. 40% of total body weight is muscle. Its cells are long and narrow, known as fibers.