Sympathetic Nervous System Lecture Notes

Overview

• Autonomic Nervous System (ANS): Comprises sympathetic (fight or flight) and parasympathetic (rest and digest) systems, part of the peripheral motor division.
• Focus: Detailed study of sympathetic nervous system, exploring its structures and functions.

• Sympathetic Ganglia:
  • Paravertebral Ganglia/sym chain/trunk: Located laterally to the spinal cord, forming a sympathetic chain.
  • Has parts
  • (s,m,i) cervical ganglion,thoracic ,lumbar,sacral,cocygeal
  • In superior thorax inf cervical and thoracic combine to form stellite ganglion
  • Prevertebral Ganglia:/collateral Located in front of the vertebra and aorta.
    parts:
    Celiac ganglia,s,i mesentric ganglia,aortocorneal ganglia

Innervation Details

Head, Neck, and Thorax

• Cervical Ganglia(t1-t4): Superior, middle, and inferior, each affecting different regions.
  • Superior Cervical Ganglion: Largest, provides innervation for eye dilation (dilator pupillae), accommodation (ciliaris muscle), and reducing lacrimation,salivary
    Pathway:1)superior ganglion-post ganglionic internal carotid nerve-plexus-ciliary ganglion-eye
    2)internal caroitid plexus-deep petrosal nerve-pterigopalatine ganglion-blood vessels of lacrimal gland,gland itself,oral cavity,nasal,sinuses
    3)superior ganglion-external carotid nerve-submandibular/otic ganglion/salivary glands
    4)superior ganglion-laryngeal pharyngeal nerve-pharyngeal plexus(with vagus,gp)
    -pharynx.
  • Middle Cervical Ganglion: Small, influences thyroid and parathyroid glands.
    pathway:middle/some inf ganglion-as vasomoto nerves-thyroid,parathyroid gland
  • Inferior Cervical Ganglion: Often fused; affects heart rate and contractility
    pathway:
    1)icg- vetebral nerve-vetebralplexus
    2)superior,middle ,inferior cervical cardiac nerve-plexus
• Thoracic Ganglia: Affect heart, lungs (bronchodilation), and esophagus (reduced peristalsis).
  pathway:

1. thoracic cardiac nerve-plexus-
   2)eospegeal plexus
   3)pulmonary plexus

Abdominal and Pelvic Viscera

• Splanchnic Nerves: Preganglionic fibers bypass paravertebral ganglia to synapse at prevertebral ganglia.
• Prevertebral Ganglia:
  • **Greater splanchnic nerve-Celiac Ganglia-post gangli -**Liver (glycogenolysis), stomach,(inhibit peristaltic movt)pancreas, (decrease insulin),spleen

  • Greater splanchnic nerve -adrenal medulla (direct)-(intramural ganglion/post ganglion/chromaffin cells)

  • Lesser splanchnic nerve-Superior Mesenteric Ganglia: Inhibits GI activity.
    (Caecum colon,small intestine)
  • Least splanchnic nerve-Aorticorenal Ganglia: Affects kidneys (reduce urine production).
  • Inferior Mesenteric Ganglia: Affects lower GI tract, bladder, and reproductive organs.
• Key point:sacral splacnic nerve-inn of organs of inferior hypogastric plexus-gonads
• Adrenal Medulla: Direct stimulation by preganglionic fibers for widespread catecholamine release.

Functional Outcomes

• Fight or Flight Effects:
  • Cardiovascular: Increased heart rate and contractility.
  • Respiratory: Bronchodilation.
  • Digestive: Reduced peristalsis and secretion.
  • Urinary: Decreased urine production.
  • Reproductive: Ejaculation in males, uterine contractions in females.

Structural Relationships

• Nerve Plexuses: Interconnections between ganglia and organs.
  • Thoracic Plexuses: Cardiac, pulmonary, esophageal.
  • Abdominal/Pelvic Plexuses: Celiac, superior/inferior mesenteric, hypogastric.

pathway crux:

• Start at the spinal cord (specifically in the T1–L2 levels where sympathetic preganglionic neurons originate in the lateral horn).
• The preganglionic fiber exits the spinal cord through the ventral (anterior) root.
• It enters a small nerve branch called the white ramus communicans.
• From there, it reaches the sympathetic trunk (chain) — a paired nerve running on both sides of the spine.
• Now, the fiber can do one of three things:
  • Synapse at the same level in the sympathetic ganglion.
  • Ascend or descend to a different level of the trunk and then synapse.
  • Pass through without synapsing and go to a collateral (prevertebral) ganglion (like celiac, superior/inferior mesenteric) — this happens especially for abdominal organs.
• After synapsing, the postganglionic fiber travels:
  • Through the gray ramus communicans back to the spinal nerve (if it’s going to skin, blood vessels, sweat glands, etc.)
  • Or directly through sympathetic nerves to target organs (like the heart, lungs, or abdominal organs).