Effects of Sympathetic and Parasympathetic Stimulation on Specific Organs

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Eyes. Two functions of the eyes are controlled by the autonomic nervous system. They are (1) the pupillary opening and (2) the focus of the lens.

Sympathetic stimulation contracts the meridional fibers of the iris that dilate the pupil, whereas parasym-pathetic stimulation contracts the circular muscle of the iris to constrict the pupil.

The parasympathetics that control the pupil are reflexly stimulated when excess light enters the eyes, which is explained in Chapter 51; this reflex reduces the pupillary opening and decreases the amount of light that strikes the retina. Conversely, the sympathetics become stimulated during periods of excitement and increase pupillary opening at these times.

Focusing of the lens is controlled almost entirely by the parasympathetic nervous system. The lens is normally held in a flattened state by intrinsic elastic tension of its radial ligaments. Parasympathetic excitation contracts the ciliary muscle, which is a ringlike body of smooth muscle fibers that encircles the outside ends of the lens radial ligaments. This contraction releases the tension on the ligaments and allows the lens to become more convex, causing the eye to focus on objects near at hand. The detailed focusing mechanism is discussed in Chapters 49 and 51 in relation to function of the eyes.

Glands of the Body. The nasal, lacrimal, salivary, and many gastrointestinal glands are strongly stimulated by the parasympathetic nervous system, usually resulting in copious quantities of watery secretion. The glands of the alimentary tract most strongly stimulated by the parasympathetics are those of the upper tract, especially those of the mouth and stomach. On the other hand, the glands of the small and large intestines are controlled principally by local factors in the intestinal tract itself and by the intestinal enteric nervous system and much less by the autonomic nerves.

Sympathetic stimulation has a direct effect on most alimentary gland cells to cause formation of a concentrated secretion that contains high percentages of enzymes and mucus. But it also causes vasoconstriction of the blood vessels that supply the glands and in this way sometimes reduces their rates of secretion.

The sweat glands secrete large quantities of sweat when the sympathetic nerves are stimulated, but no effect is caused by stimulating the parasympathetic nerves. However, the sympathetic fibers to most sweat glands are cholinergic (except for a few adrenergic fibers to the palms and soles), in contrast to almost all other sympathetic fibers, which are adrenergic. Furthermore, the sweat glands are stimulated primarily by centers in the hypothalamus that are usually considered to be parasympathetic centers. Therefore, sweating could be called a parasympathetic function, even though it is controlled by nerve fibers that anatomically are distributed through the sympathetic nervous system.

The apocrine glands in the axillae secrete a thick, odoriferous secretion as a result of sympathetic stimulation, but they do not respond to parasympathetic stimulation. This secretion actually functions as a lubricant to allow easy sliding motion of the inside surfaces under the shoulder joint. The apocrine glands, despite their close embryological relation to sweat glands, are activated by adrenergic fibers rather than by cholinergic fibers and are also controlled by the sympathetic centers of the central nervous system rather than by the parasympathetic centers.

Intramural Nerve Plexus of the Gastrointestinal System. The gastrointestinal system has its own intrinsic set of nerves known as the intramural plexus or the intestinal enteric nervous system, located in the walls of the gut. Also, both parasympathetic and sympathetic stimulation originating in the brain can affect gastrointestinal activity mainly by increasing or decreasing specific actions in the gastrointestinal intramural plexus. Parasympathetic stimulation, in general, increases overall degree of activity of the gastrointestinal tract by promoting peristalsis and relaxing the sphincters, thus allowing rapid propulsion of contents along the tract. This propulsive effect is associated with simultaneous increases in rates of

Table 60-2

Autonomic Effects on Various Organs of the Body


Effect of Sympathetic Stimulation

Effect of Parasympathetic Stimulation

Eye Pupil

Ciliary muscle Glands Nasal Lacrimal Parotid

Submandibular Gastric Pancreatic Sweat glands Apocrine glands Blood vessels Heart Muscle

Coronaries Lungs Bronchi Blood vessels Gut Lumen Sphincter Liver

Gallbladder and bile ducts Kidney Bladder Detrusor Trigone Penis

Systemic arterioles Abdominal viscera Muscle

Skin Blood

Coagulation Glucose Lipids Basal metabolism Adrenal medullary secretion Mental activity Piloerector muscles Skeletal muscle

Fat cells


Slight relaxation (far vision) Vasoconstriction and slight secretion

Copious sweating (cholinergic) Thick, odoriferous secretion Most often constricted

Increased rate

Increased force of contraction Dilated (|32);constricted (a)


Mildly constricted

Decreased peristalsis and tone Increased tone (most times) Glucose released Relaxed

Decreased output and renin secretion

Relaxed (slight)




Constricted (adrenergic a) Dilated (adrenergic b2) Dilated (cholinergic) Constricted

Increased Increased Increased

Increased up to 100% Increased Increased Contracted

Increased glycogenolysis Increased strength Lipolysis


Constricted (near vision)

Stimulation of copious secretion (containing many enzymes for enzyme-secreting glands)

Sweating on palms of hands None

Most often little or no effect Slowed rate

Decreased force of contraction (especially of atria) Dilated

Constricted ? Dilated

Increased peristalsis and tone Relaxed (most times) Slight glycogen synthesis Contracted None




None None


None None None None None None None None

None secretion by many of the gastrointestinal glands, described earlier.

Normal function of the gastrointestinal tract is not very dependent on sympathetic stimulation. However, strong sympathetic stimulation inhibits peristalsis and increases the tone of the sphincters. The net result is greatly slowed propulsion of food through the tract and sometimes decreased secretion as well—even to the extent of sometimes causing constipation.

Heart. In general, sympathetic stimulation increases the overall activity of the heart. This is accomplished by increasing both the rate and force of heart contraction.

Parasympathetic stimulation causes mainly opposite effects—decreased heart rate and strength of contraction. To express these effects in another way, sympa thetic stimulation increases the effectiveness of the heart as a pump, as required during heavy exercise, whereas parasympathetic stimulation decreases heart pumping, allowing the heart to rest between bouts of strenuous activity.

Systemic Blood Vessels. Most systemic blood vessels, especially those of the abdominal viscera and skin of the limbs, are constricted by sympathetic stimulation. Parasympathetic stimulation has almost no effects on most blood vessels except to dilate vessels in certain restricted areas, such as in the blush area of the face. Under some conditions, the beta function of the sym-pathetics causes vascular dilation instead of the usual sympathetic vascular constriction, but this occurs rarely except after drugs have paralyzed the sympathetic alpha vasoconstrictor effects, which, in blood vessels, are usually far dominant over the beta effects.

Effect of Sympathetic and Parasympathetic Stimulation on Arterial Pressure. The arterial pressure is determined by two factors: propulsion of blood by the heart and resistance to flow of blood through the peripheral blood vessels. Sympathetic stimulation increases both propulsion by the heart and resistance to flow, which usually causes a marked acute increase in arterial pressure but often very little change in long-term pressure unless the sympa-thetics stimulate the kidneys to retain salt and water at the same time.

Conversely, moderate parasympathetic stimulation via the vagal nerves decreases pumping by the heart but has virtually no effect on vascular peripheral resistance. Therefore, the usual effect is a slight decrease in arterial pressure. But very strong vagal parasympathetic stimulation can almost stop or occasionally actually stop the heart entirely for a few seconds and cause temporary loss of all or most arterial pressure.

Effects of Sympathetic and Parasympathetic Stimulation on Other Functions of the Body. Because of the great importance of the sympathetic and parasympathetic control systems, they are discussed many times in this text in relation to multiple body functions. In general, most of the entodermal structures, such as the ducts of the liver, gallbladder, ureter, urinary bladder, and bronchi, are inhibited by sympathetic stimulation but excited by parasympathetic stimulation. Sympathetic stimulation also has multiple metabolic effects such as release of glucose from the liver, increase in blood glucose concentration, increase in glycogenolysis in both liver and muscle, increase in skeletal muscle strength, increase in basal metabolic rate, and increase in mental activity. Finally, the sympathetics and parasympathetics are involved in execution of the male and female sexual acts, as explained in Chapters 80 and 81.

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    Does the skin arteriole dialates during parasympathetic stimulation?
    3 years ago
  • Daniel
    How sympathetic and parasympathetic stimulation on system organs?
    3 years ago
  • Pauli
    Does the parasympathetic nervous system cause sweat secretion?
    3 years ago
  • max
    Why does saliva becomes during sympathetic effect (thick decreased secretion?
    3 years ago
  • daisy
    What is the effect of sympathetic stimulation on heart, bronchi and G I T ?
    3 years ago
  • heike
    What is the effect of sympathetic NS on the body?
    3 years ago
    What happens to the apocrine gland during parasympathetic nervous system?
    3 years ago
  • iain
    How does the sympathetic nervous system dilates the iris?
    3 years ago
  • zane
    What is the effect of parasympathetic nerve stimulation on the heart and iris?
    2 years ago
  • Louise
    What are the general effects of sympathetic and parasympathetic stimulation on blood vessels?
    2 years ago
  • dennis
    What effect does the sympathetic have on pupil of an eye?
    2 years ago
  • eero
    What is the effect of sympathetic and parasympathetic stimulation on the pupil of the eye?
    2 years ago
    What organs are affected by sympathetic tone?
    1 year ago
  • arttu manninen
    What happens to the heart and sphincters in parasympathetic stimulation?
    1 year ago
  • chica
    Why no effect if sympathetic on lacrimal gland?
    1 year ago
  • saare
    Is muscle contration sympathetic or parasympathetic action?
    1 year ago
    Is watery eyes sympathetic or parasympathetic?
    12 months ago
  • Antoni
    What does alpha stimulation do to liver?
    11 months ago
  • oscar
    How does the sympathetic nervous system affect the iris and pupil?
    11 months ago
  • Felix
    How does sympathetic stimulation affect trachea and bronchi?
    11 months ago
  • Cara
    How does the sympathetic nervous system control the lacrimal gland?
    10 months ago
    What are the effects (responses) of the sympathetic stimulation?
    10 months ago
  • kaarle pitk
    What are theeffects reposnses of the sympathetic stimulation?
    10 months ago
  • Fernando
    Which organ/region have no parasympathetic stimulation?
    9 months ago
  • Nicol
    What is the effect of sympathetic and parasympathetic stimulation on the sweat gland.?
    8 months ago
  • Mathilda
    What is the effect of parasympathetic stimulation on the stomach?
    8 months ago
  • frans
    Does sympathetic activation cause watery eyes?
    8 months ago
  • Stefanie
    What type of muscle are the constrictor pupil muscle fibres are sympathetic or parasympathetic?
    8 months ago
  • castore
    Which area of the heart recieves little to no sympathetic stimulation?
    7 months ago
  • Berta
    What effect does the parasympathetic system have on the liver?
    6 months ago
  • katelyn
    What is sympathetic stimulatio in the pupil responsible for?
    6 months ago
  • MAYA
    What effect does the sympathetic have on the eyes?
    6 months ago
  • Jamie Ferguson
    What effect does parasympathetic stimulation have on the quantity and composition of saliva?
    6 months ago
  • maxima
    How do does sympathetic and parasympathetic ns influnce ureter control?
    6 months ago
  • jukka-pekk
    What is the effect of the parasympathic stimulation on the pumping mechanism of the heart?
    5 months ago
  • iago
    Which effect results from sympathetic stimulation?
    5 months ago
  • guarino
    What would the effect be for the eyes on the parasympathetic nervous system?
    5 months ago
  • oliwia milne
    What are roles of the parasympathetic in reproductive?
    4 months ago
  • clarence lane
    What are the physiologic results of sympathetic stimulation?
    4 months ago
  • ben
    How does parasympathetic control the liver?
    4 months ago
  • markku jauho
    How does parasympathetic nervous system regulate the tear gland?
    4 months ago
  • SARA
    Which effect results from parasympathetic stimulation?
    3 months ago
  • Matthew
    How does the nervous system effect the muscles?
    3 months ago
  • elisabeth
    What effect of sympathetic stimulation of the heart have on blood pressure?
    3 months ago
  • Marmaduc
    What effect does alpha stimulation have on pupils?
    2 months ago
  • steven
    How does the sympahthic nervous system regulate blood vessles?
    2 months ago
  • cosma palermo
    Which blood pressure is greater sympathetic or parasympathetic stimulation?
    2 months ago
    How does the nervous sytem effect eyes?
    2 months ago
  • olle sepp
    Is increased sweat secretion effect of the parasympathetic nervous system?
    1 month ago
  • Terttu Peltonen
    What are the psysiologic result of parasympathetic stimulations?
    1 month ago
  • Generosa
    Is the dialiation of the eyeball an effect of the sympathetic or perisympathetic?
    1 month ago
  • christina beyer
    Are sweat glands controlled by sympathetic or parasympathetic.?
    26 days ago
  • russom
    What does the sympathetic nervous system do to your eyes?
    22 days ago
    What is the effect of parasympathetic nerve stimulation upon application?
    17 days ago
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    Does parasympathetic nervous system constrict blood vessel?
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  • saare
    Does parasympathetic contract arterioles?
    15 days ago
  • bisrat
    Does sympathetic cause sweat glands to dilate?
    13 days ago
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    8 days ago
  • sheshy
    Does eurostress impact the Sympathetic Nervous system?
    6 days ago
  • tommy
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    2 days ago

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