Autonomic+Innervation+of+Abdomen+and+Pelvis

=**Objectives**=


 * 1. Review the basic organization of the sympathetic and parasympatheic division of the ANS.**

Visceral efferent components of the autonomic nervous system are divided into sympathetic, parasympathetic, and enteric systems. All these divisions are involved in the control of involuntary muscles somewhere in the body.

The sympathetic division is involved in the fight or flight response while the parasympathetic is involved in rest and digest.


 * **Feature** || **Sympathetic** || **Parasympathetic** ||
 * Location of preganglionic neurons || Spinal cord, lateral horn T1-L2 || Brainstem and spinal cord, cranial nerves III, VII, IX, and X, lateral horn S2-S4 ||
 * Location of postganglionic neurons || Paravertebral ganglia adjacent to the vertebral column and prevertebral ganglia in front of the vertebral column || Named ganglia cranial nerves III, VII, and IX and terminal ganglia in the wall of the organ ||
 * Neurotransmitter || Presympathetic: Ach, Postsympathetic: NE || Presympathetic: Ach, Postsympathetic: Ach ||
 * Terminal Distribution || Blood vessels, sweat and salivary glands, arector pilli smooth muscle, skin in general || Not to blood vessels, mucous, lacrimal, GI, and salivary glands, not skin in general ||


 * 2. What is the general organization of sympatheic innervation to abdomenal viscera?**

Preganglionic sympathetic visceral efferent originates in the laternal horn of the spinal cord at levels T1-L2 and travels out through the ventral horn to the spinal nerve and exits via white ramus into a paravertebral ganglion. It then continues without synapsing through a Splanchnic nerve to a Prevertebral ganglion where it synapses with a post ganlionic neuron. The post ganglionoic neuron then follows blood vessals to the abdominal viscera.


 * 3. Describe the following terms:**

__Thoracic Splanchnic__: Nerves that arise from the sympathetic trunk in the thorax and travel inferiorly to provide sympathetic innervation to the abdomen. The nerves contain preganglionic sympathetic and visceral afferent fibers.

__Lumbar Splanchnic__: Nerves that arise from the lumbar part of the sympathetic trunk and travel to an adjacent plexus near the aorta. These nerves contain preganglionic sympathetic and visceral afferent fibers.

__Prevertebral Ganglia__: Sympathetic ganglia which lie between the sympathetic chain and the organ of supply. They are the site of relay of the preganglionicsympathetic fibres that supply abdominal and pelvic viscera.

__Paravertebral Ganglia__: Ganglia lieing along the spinal cord which recieve presynaptic sympathetic fibers and is the location for synapse of somatic efferent fibers. Viceral efferent fibers use paravertebral ganglia as a path to prevertebral ganglia where they synapse.


 * 4. What is the distribution of the vagus nerve in the abdomen? Describe the formation and distribution of pelvic splanchnic nerves. What is their distribution?**

The left and right vagus nerves descend through the thorax along the esophagous with the right branch forming the posterior vagal trunk and the left forming the anterior vagal trunk both passing throught the esophageal hiatus. The vagus nerves inervate the stomach and contribute to the aortic plexus. Pelvic splanchnic nerves are derived from the anterior rami of spinal nerves S2-S4. These pelvic splanchnic nerves travel inferiorly to inerveate the hindgut, as well as contributing parasympathetic inervation to the inferior hypogastric plexus which inervates pelvic viscera.


 * 5. What is the basic organization of sympathetic innervation to pelvic viscera?**

The sympathetic inervation is derived from lumbar splanchnic nerve originating at L1-L2 which synapses in the superior hypogastric plexus and the sacral splanchnic nerve originating at S2-4 and traveling through the inferior hypogastric plexus to inervate its effector.


 * 6. Describe the following terms:**

__Superior Hypogastric Plexus__: Plexus of nerves situated in front of the last lumbar vertebra and the promontory of the sacrum, between the two common iliac arteries, and is formed by the union of numerous filaments, which descend on either side from the aortic plexus, and from the lumbar splanchnic nerves; it divides, below, into two lateral portions which travel inferiorly as the so-called hypogastric nerves, which end as the inferior hypogastric plexus.

__Hypogastric Nerve__: inferior portion of the superior hypogastric plexus divided into left and right nerves descending inferiorly to form the inferior hypogastric plexus in the pelvis.

__Inferior Hypograstric Plexus__: is a bilateral plexus of nerves that supplies the viscera of the pelvic cavity.

__Sacral Splanchnic__: primarily preganglionic symathetic fibers that come off the sympathetic chain and synapse with the inferior hypogastric plexus.


 * 7. What is the basic organization of parasympathetic innervation to pelvic viscera?**

Pelvic splanchnic nerves are derived from the anterior rami of spinal nerves S2-S4. These pelvic splanchnic nerves contribute parasympathetic inervation to the inferior hypogastric plexus which inervates pelvic viscera.


 * 8. What is a visceral afferent? What sensations does this afferent mediate?**

Visceral afferent is sensation carried along autonomic nerve fibers towards the CNS from the viscera. Their path for detection of pain is similar to the sympathetic visceral efferent path for that structure however it has its cell body in the DRG and synapses in the CNS. This sensation detects "state of organ" follows a pathway similar to parasympathetic visceral efferent for that structure. Their close asociation with somatic efferent fibers in the DRG lead to referred pain.


 * 9. As an example, describe the course of a visceral afferent fiber carrying information about pain from the duodenum. Where would pain from the duodenum be referred?**

The pain detected in the duodenum would follow the path of the sympathetic visceral efferent with a single pseudopolar neurton traveling from the duodenum throught the celiac ganglia along the greater splanchnic nerve throught the paravertebral ganglion, white ramus, dorsal root, DRG, and into the CNS. This pain would be referred to the T8-T12 dermatome.


 * 10. As an example, describe the course of a visceral afferent carrying information about stretch of the intestinal wall.**

The visceral efferent stretch would be carried via the parasympathetic visceral efferent inervation of the organ. For the intestinal wall this would involve traveling back through pelvic splachnic nerves or the vagus nerve parting ways at thedorsal root, continues on to the DRG, and into the CNS.

Summary Tables:
Sympathetic Abdomen:
 * **Organs** || **Preganglionic cell body** || **Preganglionic fibers** || **Prevertebral ganglion** || **Postganglion fibers** ||
 * Foregut- celiac axis || T5-T9 || Greater splanchnic n. || Celiac ganglion Celiac plexus || along celiac a. ||
 * Midgut- superior mesenteric || T10-T11 || Lesser splanchnic n. || Superior mesenteric ganglion || Along superior mesenteric a. ||
 * Hindgut- inferior mesenteric || L1-L2 || Lumbar splanchnic n. || Inferior mesenteric ganglion || Along inferior mesenteric a. ||
 * Kidneys, gonads || T12 || Least splanchnic n. || Aorticorenal || Renal artery gonadal artery ||
 * Suprarenal gland (medulla) || T8-T12 || Greater, lesser, and least || None- unique case || Medulla (special cells) ||

Parasympathetic Abdomen:
 * **Organs** || **Preganglionic neuronal cell body** || **Preganglionic fibers (axon)** || **Ganglion** || **Postganglionic fibers** ||
 * Foregut || Brainstem CN 10 || Vagus || Terminal || Short within the wall ||
 * Midgut || Brainstem CN 10 || Vagus || Terminal || Wall of organ ||
 * Hindgut || S2-S4 lateral horn || Pelvic splanchinic || Terminal || Wall of organ ||
 * Kidneys, gonads || Brainstem CN 10- unknown || Vagus || Terminal || Wall of organ ||
 * Suprarenal gland || No parasympathetic ||  ||   ||

Sympathetic Pelvis:
 * **Organs** || **Preganglionic neuronal cell body** || **Preganglionic fibers (splanchnic nerve** || **Autonomic ganglion** || **Postganglionic fibers** ||
 * Bladder || Lateral horn L1-L2 || Lumbar splanchnic n. to superior hypogastric plexus || Small ganglia in superior hypogastric plexus || Hypogastric n. to inferior hypogastric plexus to blood vessels (to organs) ||
 * rectum, uterus fundus, vagina, seminal vesicles, etc. All the same path. || Lateral horn L1-L2 || Descend in the chain to sacral region || Synapse in paravertebral ganglia in the sacral region || Use sacral splanchnic to enter toe inferior hypogastric plexus to organ ||

Parasympathetic Pelvis:
 * **Organs** || **Preganglionic neuronal cell body** || **Preganglionic fibers** || **Ganglion** || **Postganglionic fibers** ||
 * Bladder, rectum, uterus, vagina, seminal vesicles || Lateral horn of S2-S4 || Pelvis splanchnic n. to the inferior hypogastric plexus distributed to organs via individual plexuses || Terminal ganglia || Distributed in the wall of the organ ||