SMOOTH MUSCLE

• Upon the basis of light microscopic structure , the smooth muscle is classified into:

Non –striated muscle cells, which do not show cross-striations of alternating light and dark bands.

• They are involuntary.• Also called as visceral muscles.

SHAPE OF SMOOTH MUSCLE

• The smooth muscle fibers (cells) are fusiform in

shape (i.e. tapering at both ends).

SIZE OF SMOOTH MUSCLE

• The average greatest diameter of a smooth

muscle fiber is about 6mm.• However, the length of the smooth muscle fibers

is highly variable in different locations , like in the walls of small blood vessels it is about 20mm and in the walls of the intestine it is about 200mm.

• Longest smooth muscle fibers are found in the walls of pregnant uterus where they may reach a length of 500mm.

• The smooth muscles fibers are usually arranged in the form of sheet or bands.

SARCOLEMMA: The cell membrane of each smooth muscle fiber is called sarcolemma.

NUCLEUS: Each smooth muscle cell contains a single rod-shape nucleus, which is located in the central thick portion.

SARCOPLASM: • The cytoplasm of the soomth muscle fiber is

known as sarcoplasm. • The sarcoplasm of the smooth muscle cell

contains a contractile apparatus of thick and thin filaments.

CONTRACTILE APARATUS:It enables the smooth muscles to undergo shortening as and when require.Thin filament and thick filaments:Composed of protein called ACTIN and MYOSIN //.

• The sarcoplasm contains:MitochondriaA few elements of rough endoplasmic reticulumSome free ribosome’sA small golgi apparatus &Some glycogen granules.

NERVE SUPPLY OF SMOOTH MUSCLE• The smooth muscle is supplied by the

sympathetic and parasympathetic divisions of autonomic nervous system.

• All the nerve fibers are postganglionic.

FUNCTIONS OF SMOOTH MUSCLE• The smooth muscle in the uterus helps women

to push out her baby.• In the bladder, to push out urine.• Smooth muscle determines the flow of blood

in the arteries.• Also help to move food through the digestive

track.• And regulates air flow in lungs.