37. GA - ANS Innervation of the Abdomen
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Questions and Answers

Which type of receptors detect distention of the gut wall in the GI tract?

  • Thermoreceptors
  • Photoreceptors
  • Mechanoreceptors (correct)
  • Chemoreceptors

    • Where are the cell bodies of vagal sensory neurons located?

  • In the pelvic splanchnic ganglia
  • In the thoracic region
  • In the spinal cord
  • Near the brainstem (correct)

    • What is the primary function of pain receptors in the GI tract?

  • To sense excessive stretch or damage (correct)
  • To detect temperature changes
  • To monitor chemical composition
  • To regulate blood flow

    • Referred pain is primarily due to the convergence of which types of nerves?

    <p>Visceral afferent and somatic afferent</p> Signup and view all the answers

    At which spinal levels are the cell bodies of pain receptors from the GI tract located?

    <p>T5-L2</p> Signup and view all the answers

    Which type of fibers primarily increase gastrointestinal peristalsis and secretion?

    <p>Parasympathetic Autonomic Nerves</p> Signup and view all the answers

    Visceral pain from the abdomen is usually referred to which area of the body?

    <p>Body wall</p> Signup and view all the answers

    What component of the autonomic nervous system decreases GI motility and gland secretion?

    <p>Sympathetic Autonomic Nervous System</p> Signup and view all the answers

    Which type of information do visceral afferent fibers primarily convey?

    <p>Reflex information and pain sensations</p> Signup and view all the answers

    The intrinsic nervous system of the gastrointestinal tract is known as what?

    <p>Enteric nervous system</p> Signup and view all the answers

    What role do ANS fibers play in the gastrointestinal tract?

    <p>Modify digestive secretions and peristalsis</p> Signup and view all the answers

    Which cranial nerve carries visceral afferents from the gut to the medulla?

    <p>Vagus Nerve (CN X)</p> Signup and view all the answers

    What is the primary function of the enteric plexus within the GI walls?

    <p>Independently regulate GI motility and secretions</p> Signup and view all the answers

    What is the origin of preganglionic parasympathetic fibers for the distal GI tract?

    <p>Brainstem and spinal cord S2-S4</p> Signup and view all the answers

    Which neurotransmitter is released by preganglionic sympathetic axons?

    <p>Acetylcholine</p> Signup and view all the answers

    From which spinal levels do preganglionic sympathetic fibers originate?

    <p>T5-L2</p> Signup and view all the answers

    What type of ganglion is associated with postganglionic sympathetic neurons in the abdomen?

    <p>Prevertebral sympathetic ganglion</p> Signup and view all the answers

    How do preganglionic parasympathetic fibers reach the GI tract?

    <p>Through the Vagus Nerve and Pelvic Splanchnic Nerves</p> Signup and view all the answers

    What is the main role of the sympathetic nervous system concerning the GI tract?

    <p>To inhibit secretions and reduce blood flow to the GI organs</p> Signup and view all the answers

    Where are postganglionic parasympathetic cell bodies located?

    <p>Near or within target organs</p> Signup and view all the answers

    What area of the GI tract is innervated by fibers originating from the brainstem?

    <p>Esophagus, stomach, and small intestine</p> Signup and view all the answers

    What is the primary function of postganglionic SANS axons from the prevertebral ganglia?

    <p>To synapse on neurons of the enteric plexus in the gut wall</p> Signup and view all the answers

    Which of the following ganglia is NOT considered a prevertebral ganglion affecting the abdominal viscera?

    <p>Dorsal root ganglion</p> Signup and view all the answers

    Where do preganglionic SANS axons synapse within the autonomic nervous system?

    <p>In the prevertebral ganglia</p> Signup and view all the answers

    What anatomical feature do prevertebral ganglia share regarding their location?

    <p>They are positioned along the abdominal aorta anterior to the vertebral column</p> Signup and view all the answers

    Which of the following spinal levels do preganglionic SANS axons originate from?

    <p>T5-L2</p> Signup and view all the answers

    Which nerve is primarily associated with the thoracic sympathetic trunk?

    <p>Greater splanchnic nerve</p> Signup and view all the answers

    What type of neurons are primarily involved in the postganglionic SANS pathway?

    <p>Postganglionic autonomic neurons</p> Signup and view all the answers

    Which option best describes the route of preganglionic SANS axons after they enter the sympathetic trunk?

    <p>They do not synapse and continue through to prevertebral ganglia</p> Signup and view all the answers

    Which spinal cord levels correspond to the spleen?

    <p>T6-T8</p> Signup and view all the answers

    What is the primary function of the enteric nervous system?

    <p>Control of peristalsis and gland secretion</p> Signup and view all the answers

    Which organ is located in the epigastric region or right hypochondrium and has spinal cord levels attributed to it in the range of T6-T9?

    <p>Liver or gallbladder</p> Signup and view all the answers

    Which spinal cord levels are associated with the kidney?

    <p>T10-L2</p> Signup and view all the answers

    Why is liver or gallbladder pain sometimes referred to the shoulder?

    <p>Common pathways in the nervous system</p> Signup and view all the answers

    Which organ is primarily associated with T10-T11 spinal cord levels?

    <p>Cecum</p> Signup and view all the answers

    What type of nerve fibers travel to the gut wall along with the intestinal arteries?

    <p>Postganglionic SANS fibers</p> Signup and view all the answers

    Which quadrant primarily contains the sigmoid colon?

    <p>Left lower quadrant</p> Signup and view all the answers

    Study Notes

    Innervation of the Abdominal Viscera

    • The abdominal viscera, including the gastrointestinal tract and accessory organs, are innervated by the autonomic nervous system (ANS).
    • ANS fibers regulate gastrointestinal motility (peristalsis), secretions (enzymatic and mucus), and blood flow.
    • The parasympathetic nervous system (PANS) increases gastrointestinal peristalsis and gland secretion.
    • The sympathetic nervous system (SANS) decreases gastrointestinal peristalsis and gland secretion, and also reduces blood flow to the viscera.
    • The gastrointestinal tract has its own intrinsic nervous system called the "enteric plexus" or "enteric nervous system."
    • The enteric nervous system is located within the gastrointestinal walls, and the ANS modifies its activities.
    • Visceral afferent fibers (VA fibers) carry gastrointestinal reflex information to the medulla via the vagus nerve (CN X).
    • VA fibers carry pain information to the spinal cord via sympathetic nerves.
    • Visceral pain from the abdomen is usually referred to the body (soma) wall.
    • Knowledge of referred pain sites is helpful for localizing abdominal visceral pathology.

    Parasympathetic Innervation

    • Preganglionic PANS fibers originate from the brainstem (medulla) and travel in the Vagus Nerve (CN X).
    • The vagus nerve innervates the gastrointestinal tract from the esophagus to the splenic flexure of the large intestine.
    • The vagus nerve also innervates associated viscera, including the liver, gallbladder, and pancreas.
    • For the gastrointestinal tract distal to the splenic flexure, preganglionic PANS fibers arise from the S2-S4 spinal levels and travel in the Pelvic Splanchnic Nerves.
    • These fibers innervate the descending colon, sigmoid colon, and rectum.

    Sympathetic Innervation

    • Preganglionic SANS fibers originate from the T5-L2 spinal levels and innervate the entire gastrointestinal tract.
    • These fibers also innervate the liver, gallbladder, and pancreas.
    • The preganglionic SANS fibers travel via thoracic splanchnic (greater, lesser, least) and lumbar splanchnic nerves.
    • The main prevertebral SANS ganglia affecting the abdominal viscera are the celiac, aorticorenal, superior mesenteric, and inferior mesenteric ganglia.

    Location of Ganglia

    • Preganglionic cell bodies for the PANS are located in the brainstem and S2-S4 spinal cord.
    • Preganglionic cell bodies for the SANS are located in the T5-L2 spinal cord.
    • Postganglionic cell bodies for the PANS are located in the terminal parasympathetic ganglia within the organs they innervate.
    • Postganglionic cell bodies for the SANS are located in the prevertebral sympathetic ganglia along the abdominal aorta.

    Neurotransmitters

    • Preganglionic axons of both the PANS and SANS release acetylcholine (Ach).
    • Postganglionic axons of the PANS release Ach.
    • Postganglionic axons of the SANS release norepinephrine (NE).

    Receptors

    • Receptors that respond to Ach include muscarinic (M1, M3) receptors.
    • Receptors that respond to NE include alpha (a1, a2) and beta (b1, b2) adrenergic receptors.

    Anatomy of Abdominal Autonomics

    • Preganglionic SANS axons originate from the sympathetic cell column in the spinal cord at levels T5-L2.
    • These axons enter the sympathetic trunk via the white rami communicantes at the same spinal level as their cell body origin.
    • Preganglionic SANS axons exit the anterior surface of the sympathetic ganglion as splanchnic nerves.
    • Splanchnic nerves travel to prevertebral ganglia located along the abdominal aorta and its major branches.
    • The prevertebral ganglia include the greater, lesser, and least splanchnic nerves, as well as the lumbar and sacral splanchnic nerves.
    • Postganglionic SANS axons from the prevertebral ganglia exit and use arterial branches to the intestines to reach the gut wall.
    • These axons then synapse on neurons of the enteric plexus.

    Visceral Afferents

    • Mechanoreceptors located in the gastrointestinal tract detect distention of the gut wall, and this information is carried to the medulla by the vagus nerve.
    • The cell bodies of these vagal sensory neurons are located in ganglia near the brainstem.
    • This sensory information is vital for gastrointestinal reflexes.
    • Mechanoreceptors located in the rectum carry stretch information to the spinal cord via the pelvic splanchnic nerves.
    • Pain receptors located in the gastrointestinal tract and accessory organs detect excessive stretch or other types of damage.
    • These receptors carry this information to the spinal cord following nerve plexuses that also convey the sympathetic motor axons.
    • The cell bodies of these sensory neurons are located in the dorsal root ganglia at spinal levels T5-L2.

    Referred Pain

    • Visceral afferent (VA) nerves carry pain signals from the internal abdominal organs to the spinal cord at the same levels that receive somatic afferent (SA) signals from the body surface.
    • This means that damage from the internal abdominal organs is often perceived as somatic pain in specific dermatome regions.
    • The dermatome levels and regional organization of the abdominal viscera are important for understanding referred pain.

    Enteric Nervous System

    • Postganglionic SANS fibers exit their respective prevertebral ganglia and travel to the gut wall with branches of the intestinal arteries.
    • Preganglionic PANS branches of the vagus and pelvic splanchnic nerves also travel with the arteries to the gut wall along with the sympathetic fibers.
    • The enteric nervous system (also called the enteric plexus) is a network of neurons located in the gut wall.
    • The enteric nervous system controls peristalsis and gland secretion.
    • It is modified by both the SANS and PANS systems.

    Hirschsprung's Disease

    • Hirschsprung's disease (congenital megacolon) is a condition characterized by the absence of ganglion cells in a segment of the colon.
    • This lack of ganglion cells prevents proper relaxation of the affected segment, leading to a buildup of stool and distention of the colon.

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    Description

    This quiz covers the innervation of the abdominal viscera, focusing on the autonomic nervous system's role in gastrointestinal function. It discusses how the parasympathetic and sympathetic nervous systems influence motility and secretion, as well as the enteric nervous system and its importance. Test your knowledge on these crucial concepts of abdominal anatomy and physiology.

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