Smooth Muscle Fibers

Spindle shaped One nucleus Organized into sheets Form the walls of: arteries veins, organs

Two sheets Longitudinal Run parallel to the axis of the organ Circular Circumference of the organ

Peristalsis Contraction and relaxation of the layers mixes substances and squeezes them through the pathway Contraction helps eliminate through: Urinary bladder Rectum Uterus Stomach cramps

Variscosities Nervous system contains bulbous swellings Release neurotransmitters Release occurs at diffuse junctions Ca+ found in extracellular fluid found in sarcolemma infoldings No striations No sarcomere Different actin and myosin No troponin Arranged in spiral affect

Contractions Unison response Provided by gap junctions (specialized electrical coupling between cells) Contain pacemaker cells Pacemaker cells can depolarize spontaneously

Mechanism follows: a.Actin and myosin interact by sliding filament mechanism b.Trigger for contraction is intracellular Ca+ rise c. Process energized by ATP d.Ca+ interacts with calmodulin (a protein) e.Calmodulin causes phosphoralation of ATP

Relaxation Takes 30 times longer than skeletal muscle Takes less than 1% of the energy than skeletal Slow ATP ases Smooth muscle tone – moderate degree of Contraction without fatiguing Low energy requirements

Neural, hormonal regulation Some neurotransmitters excite smooth muscles (Ach) (norepinephrine) Some neurotransmitters inhibit smooth muscles (norepinephrine) Some chemical stimuli cause depolarization ie: lack of O 2, histamine, excess CO 2, low pH, gastrin

Hyperplasia Smooth muscle fibers divide to increase their numbers Estrogen causes the increase in uterine size

Types of smooth muscle Single unit Visceral muscle Contracts rhythmically as a unit Electrically coupled by gap junctins Spontaneous action potentials Stress/relaxation response Multiunit Muscle fibers independent Supplied with nerve endings Responds to neural stimulation Graded contractions Airways to lungs, arteries, arrector pili, pupil size