AHE block 4 lecture 2: Parasympathetic and Visceral Sesnsory

Parasympathetic Division

• Active during times of nutrient processing, energy conservation, and return to homeostasis (anabolic)
• Axons are not components of spinal nerves or their branches

Cranial Parasympathetic

• Preganglionic cell bodies are located in brainstem nuclei
• Exit via cranial nerves
• Synapse on parasympathetic cranial ganglia
• Postganglionic axons project to target organs
• Preganglionic axons are long
• Postganglionic axons are short
• Structures include the heart, eyes, lungs, digestive organs, and enteric nervous system (NS)
• Communication occurs between cranial nerves

Cranial Nerves and Parasympathetic Function

• Communication between cranial nerves occurs, with nerves potentially receiving both sensory and motor fibers.
• Nuclei for all Cranial Nerves (CNs) are located in the brainstem, except CN I and CN II.
• Sensory and motor communication carried within CNs synapses on cranial nerve nuclei in the brainstem.
• CNs involved are III, VII, IX, and X
  • CN III (Oculomotor): Ciliary ganglia
  • CN VII (Facial): Otic ganglia
  • CN IX (Glossopharyngeal): Pterygopalatine ganglia
  • CN X (Vagus): Submandibular ganglia

Sacral Parasympathetic

• Preganglionic axons are long.
• Postganglionic axons are short.
• Structures include bladder, penis, rectum, and distal large intestine

Spinal Contribution & Pathway

• Preganglionic cell bodies for sacral parasympathetic are located in spinal cord segments S2-S4.
• Exit via anterior roots of sacral spinal nerves.
• Form pelvic splanchnic nerves from anterior rami.
• Synapse on target or intramural ganglia connected to the specific organ.

Effects of Sacral Parasympathetic

• Increased smooth muscle motility and secretory activity in the digestive tract
• Contraction of smooth muscle in bladder wall
• Erection of the clitoris and penis

Cardiac Plexus

• Originates from postganglionic axons from the sympathetic trunk, cervical ganglia (T1-T5).

Pulmonary Plexus

• Sympathetic contribution from sympathetic trunk (T1–T5), and postganglionic fibers travel to thoracic sympathetic ganglia. This contributes to bronchodilation and reduces mucus secretion.
• Parasympathetic contribution from the dorsal nucleus and CN X (vagus). This leads to bronchoconstriction and increased mucus secretion, and vasodilation in pulmonary vessels.

Esophageal Plexus

• Receives no sympathetic input.
• Parasympathetic input from CN X (vagus) to innervate the smooth muscle in the inferior esophagus and cardiac sphincter (circular muscle/valve), promoting peristalsis.

Abdominal Plexuses

• Primarily interconnected through CN X (vagus).
• Sympathetic contributions originates from T5-T12.

Superior Mesenteric Plexus

• Sympathetic contribution arises from least splanchnic nerves T10-T12.
• Pathway transmits preganglionic fibers to the superior mesenteric ganglion.

Inferior Mesenteric Plexus

• Sympathetic contribution from lumbar splanchnic nerves (L1-L2 spinal segments).
• Preganglionic fibers synapse in the inferior mesenteric ganglion.

Hypogastric Plexus

• Sympathetic contribution from lumbar and sacral splanchnic nerves (L1-L2).
• Pathway: Preganglionic fibers synapse in the superior hypogastric ganglia and postganglionic fibers contribute to the inferior hypogastric plexus
• Effect: Vasoconstriction, contraction of muscles (sphincter of bladder, anus), ejaculation, and remission of erection.
• Parasympathetic contribution originates from pelvic splanchnic nerves (S2-S4), and synapses near pelvic organs
• Effect: Vasodilation, relaxation of muscles, and engorgement of the erectile tissue.

Visceral Sensation

• Integration in the CNS, triggered by visceral or somatic reflexes.
• Regulate blood pressure and chemistry by altering target organ function (e.g., heart rate).
• Most visceral sensations travel with parasympathetic fibers but pain impulses travel along side sympathetic fibers.
• Conscious sensations are often poorly localized (cramps, fullness, nausea, hunger), often caused by spasms, contractions, or chemical irritants.