Smooth Muscle Fibre | Additional Study Material for NEET PDF Download

STRUCTURE OF SMOOTH MUSCLE FIBRE

• It is spindle shaped.

• Cells are connected through gap junction.

• It contains uninucleated cytoplasm

• All cell organelles are found in cytoplasm.

• Contractile fibrils are found in the cytoplasm due to this reason this cytoplasm called sarcoplasm.

• This contractile fibre called as myofibril which found in scattered form.

• Myofibril are made up of actin & myosin but remarkably less than skeletal muscle But filaments are not placed in a highly ordered pattern so striation is absent.

• Actin is more than myosin.

• Myofibril is functional unit of involuntary muscle.

• The sarcoplasmic reticulum or L tubular system is not well developed. This makes the contraction of smooth muscles strongly dependent on the ECF Ca++ ions.

• Its contraction period is longer.

• It remain in contracted stage for longer period due to this reason muscle called Non fatigue muscle.

On the basis of structure this muscle is two types :

(1) Single Unit :-They are compact muscles where the individual cells joined together by gap junctions. Innervation is diffused or weak. Muscular activity is initiated spontaneously due to hormonal action, stretching and other stimulations. The excitation spreads by myogenic activity. Single unit smooth muscles occur in the wall of gastrointestinal tract, fallopian tube, uterus, ureter, urinary bladder. When completely denervated these smooth muscle continue contracted rhythmically.

(2) Multi Unit :-Muscle fibres occur in small groups which are inervated separately and contract independently. A muscle has, therefore, a number of small units. Multi-unit smooth muscles are found in

(i) Nictitating membrane (iris)

(ii) Pilomotor muscle in the hair follicle.

(Skin) Arteriolar Smooth Muscle – Both type of properties found