Cholinergic fibers are nerve endings thatrelease acetylcholine.Adrenergic fibers are nerve fibers thatrelease norepinephrine.
Cholinergic receptors Nicotinic receptors are acetylcholine- binding receptors that bind to nicotine. Muscarinic receptors are acetylcholine- binding receptors that bind to muscarine.
Adrenergic receptors Alpha is a type of adrenergic receptor that usually causes a stimulatory effect when it binds with norepinephrine or epinephrine. Beta adrenergic receptors usually cause an inhibitory effect when bound to NE or epinephrine.
Sympathetic andparasympathetic tone Sympathetic tone is a state of partial vasoconstriction of the blood vessels maintained by sympathetic fibers. Vasomotor fibers are sympathetic nerve fibers that regulate the contraction of smooth muscle in the walls of blood vessels.
Parasympathetic tone is a state ofparasympathetic effects that preventsunnecessary heart accelerations andpromotes normal digestive activity.
Effects of the parasympatheticand sympathetic divisions onvarious organs
Target organ/system Parasympatheic effects Sympathetic effectsEye (iris) Constricts pupils Dilates pupilsEye (ciliary mucle) Stimulates muscles for close No effect accomodation of lensGlands Stimulates secretory activity Inhibits secretory activitySweat glands No effect Stimulates copious sweatingAdrenal medulla No effect Stimulates secretion of epinephrine and norepinephrineArrector pili muscles No effect Stimulates contractionHeart muscle Decreases rate Increase rate and forceCoronary blood vessels Constricts Causes vasodilationBladder/urethra Relax urethral sphincter; Constricts urethral sphincter; promotes voiding inhibits voidingLungs Constricts bronchioles Dilates bronchioles
Target organ/system Parasympatheic effects Sympathetic effectsDigestive tract organs Increases peristalsis Decreases glandular acivity and constricts sphinctersLiver No effect Releases glucose into bloodGall bladder Stimulates bile secretion Inhibits bile secretionKidney No effect Decreases urine output; vasoconstrictionPenis Causes erection Causes ejaculationVagina/clitoris Causes erection Reverse peristalsisBlood vessels No effect Constricts blood vessels, increases blood pressureBlood coagulation No effect Increases coagulationCellular metabolism No effect Increases metabolic rateAdipose tissue No effect Stiulate lipolysisMental activity No effect Increases altertness