SMOOTH MUSCLE

RAMYA.H.1ST M.Sc. Food & Nutrition

DISTRIBUTION OF SMOOTH

MUSCLE

Non-striated(plain) and involuntary. present in almost all the organs in the form of sheets,

bundles or sheaths around other tissues. Structures in which smooth muscle fibers are

present:1. Wall of organs like esophagus, stomach and

intestine in the GIT.2. Ducts of digestive glands.3. Trachea, bronchial tube and alveolar ducts of

respiratory tract.4. Ureter, urinary bladder and urethra in excretory

system.5. Wall of the blood vessels in circulatory system.6. Mammary glands, uterus, genital ducts, prostate

gland and scrotum in the reproductive system. 7. Iris and ciliary body of the eye.

FUNCTIONS OF

SMOOTH MUSCLE

In Cardiovascular systemAround the blood vessels regulate blood pressure and blood flow. In Respiratory systemContraction and relaxation of smooth muscle of air passage regulate inflow and outflow of air. In Digestive systemHelps in the movement of food substances, mixing it with digestive juices and elimination of unwanted substances. In Renal systemRegulate renal blood flow and glomerular filtration. Propels urine from kidneys to urinary bladder through ureter. In Reproductive systemIn males, it facilitates the movement of sperms. In females, it accelerates the movement of ovum into uterus through fallopian tube.

STRUCTURE OF SMOOTH

MUSCLE

Fusiform or elongated cells 2-5 microns in diameter & 50-200 microns in length Single and elongated nucleus, centrally placed Contractile proteins –actin, myosin and

tropomyosin. thick and thin filaments-present, not arranged in

orderly fashion like skeletal muscle. Thick filaments formed by myosin. Thin filaments formed by actin and tropomyosin.

Dense bodies-formed by the protein desmin. Attached to thin filaments. Scattered in sarcoplasm. Not arranged in straight line.

Covering and tendons- covered by connective tissue. Tendons absent.

TYPES OF SMOOTH MUSCLE

1. Single unit or visceral smooth muscle.

2. Multiunit smooth muscle.

SINGLE UNIT

SMOOTH MUSCLE

In an organ smooth muscle fibers functions as one unit.(all the muscles fibers of an organ, contracts and relax together)

Fibers have many interconnecting gap junctions (ions move freely). Thus a functional syncytium is developed.

Its presence is more common in the body than multiunit smooth muscle.

Fibers are arranged in sheets or bundles. Pace maker cells –present, which are self

excitable. So, spontaneous rhythmic contractions occur.

Situation-small blood vessels, walls of hollow organs such as GIT, urinary system, reproductive system, respiratory system.

Control of action-myogenic

MULTIUNIT SMOOTH MUSCLE

Individual fibers. Function independently.(contracts and relaxes on its

own) No gap junctions, each muscle fiber is innervated

by single nerve ending. Outer membrane made up of glycoprotein(insulate

and separate the muscle fibers from one another) Control of action-neurogenic(stimulated by nerves of

autonomic nervous system) Pacemaker cells-absent. No spontaneous

contractions. Situation-ciliary muscles of the eye, iris of the eye.