Organs with Dual Innervation

Most visceral organs receive dual innervation—they are innervated by both sympathetic and parasympathetic fibers. In this condition, the effects of the two divisions of the autonomic system may be antagonistic, complementary, or cooperative (table 9.7).

Antagonistic Effects

The effects of sympathetic and parasympathetic innervation of the pacemaker region of the heart is the best example of the antagonism of these two systems. In this case, sympathetic and parasympathetic fibers innervate the same cells. Adrenergic stimulation from sympathetic fibers increases the heart rate, whereas the release of acetylcholine from parasympathetic fibers decreases the heart rate. A reverse of this antagonism is seen in the digestive tract, where sympathetic nerves inhibit and parasympa-thetic nerves stimulate intestinal movements and secretions.

The effects of sympathetic and parasympathetic stimulation on the diameter of the pupil of the eye are analogous to the reciprocal innervation of flexor and extensor skeletal muscles by somatic motor neurons (see chapter 12). This is because the iris contains antagonistic muscle layers. Contraction of the radial muscles, which are innervated by sympathetic nerves, causes dilation;

The Autonomic Nervous System 235

contraction of the circular muscles, which are innervated by parasympathetic nerve endings, causes constriction of the pupils (chapter 10, fig. 10.27).

Complementary and Cooperative Effects

The effects of sympathetic and parasympathetic nerves are generally antagonistic; in a few cases, however, they can be complementary or cooperative. The effects are complementary when sympathetic and parasympathetic stimulation produce similar effects. The effects are cooperative, or synergistic, when sympathetic and parasympathetic stimulation produce different effects that work together to promote a single action.

The effects of sympathetic and parasympathetic stimulation on salivary gland secretion are complementary. The secretion of watery saliva is stimulated by parasympathetic nerves, which also stimulate the secretion of other exocrine glands in the digestive tract. Sympathetic nerves stimulate the constriction of blood vessels throughout the digestive tract. The resultant decrease in blood flow to the salivary glands causes the production of a thicker, more viscous saliva.

The effects of sympathetic and parasympathetic stimulation on the reproductive and urinary systems are cooperative. Erection of the penis, for example, is due to vasodilation resulting from parasympathetic nerve stimulation; ejaculation is due to stimulation through sympathetic nerves. The two divisions of the autonomic system thus cooperate to enable sexual function in the male. They also cooperate in the female; clitoral erection and vaginal secretions are stimulated by parasympathetic nerves, whereas orgasm is a sympathetic nerve response, as it is in the male.

There is also cooperation between the two divisions in the micturition (urination) reflex. Although the contraction of the urinary bladder is largely independent of nerve stimulation, it is promoted in part by the action of parasympathetic nerves. This reflex is also enhanced by sympathetic nerve activity, which increases the tone of the bladder muscles. Emotional states that are accompanied by high sympathetic nerve activity (such as extreme fear) may thus result in reflex urination at bladder volumes that are normally too low to trigger this reflex.

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  • seren
    What is the advantage of dual innervation?
    5 years ago
  • sointu
    How is the heart rate a good example of dual innervation in the autonomic nervous system?
    5 years ago
    Is orgasm sympathetic or asympathetic?
    5 years ago
  • Alice
    What organs are dual innervated?
    5 years ago
    What organs receive dual innervation?
    5 years ago
  • ali
    Which organs are innervated by both parasympathetic and sympathetic?
    5 years ago
  • josefina
    Is sex an antagonistic effect or cooperative effect?
    5 years ago
  • natalino
    What muscles innervated by parasympthetic nerves?
    5 years ago
  • Walter
    What is a double reciprocal innervation in physiology?
    5 years ago
  • Gabrielle Findlay
    Which of organ receive dual innervation?
    4 years ago
  • sarah semhar
    What is dual physiology?
    4 years ago
  • fedra baresi
    What organ receives dual innervation?
    4 years ago
  • ghenet
    What digestive function is uder dual innervation?
    4 years ago
  • niina
    When two divisions dual innervate and work with each other?
    4 years ago
    Which visceral organs reeive dual innervation?
    3 years ago
  • gaetana
    What are teo organs that recieve dual autonomic innervation?
    2 years ago
  • Katrin Gerber
    What is the response to an organ with dual innervation?
    1 year ago
  • rosamunda
    What body system receives dual innervation?
    1 year ago
  • Tony
    What is the organs receives sympathetic and parasympathetic?
    1 year ago
  • Eliisa
    Does the heart receive dual autonomic innervation?
    1 year ago
  • anssi
    What organ receives double blood supply?
    9 months ago
  • ulrike
    How reciprocal innervation affect different organs of the body?
    8 months ago
  • Juhani
    How symphatetic system and parasymphatetic system work antagonistically with examples?
    8 months ago
  • ariam
    What is the value of having dual innervation of most organs by the two divisions of the ans?
    6 months ago
  • ilaria
    Which organs receive dual innervation of parasympathetic and sympathetic?
    5 months ago
  • tarquinia li fonti
    Where antagonistic effect and coorperative eefect promote on target organ?
    3 months ago
  • Erling Boffin
    What is the advantage of dual innervation by autonomic nervous system?
    2 months ago

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