Autonomic Nervous System – Comprehensive Study Notes

Page 1

• Introductory slide from The Ohio State University College of Medicine.
• Topic focus: Autonomic Nervous System (ANS).
• Visual placeholders: the number “8”, an equals sign, and the letter “B”—all design elements without conceptual weight.

Page 2 – Objectives

1. Distinguish ANS from Somatic Nervous System (SNS).

2. Define parasympathetic vs. sympathetic divisions, comparing:
   • Sites of origin.
   • Relative axon lengths.
   • Location of ganglia.

3. Detail adrenal medulla; explain why it qualifies as a modified sympathetic ganglion.

4. Deep-dive into parasympathetic division:
   • Locations of pre- and post-ganglionic cell bodies.
   • Route of signal transmission.
   • Innervation targets and physiologic effects.
   • Distinction of abdominopelvic visceral outflow, pelvic splanchnic nerves, terminal ganglia, and intramural ganglia.

5. Deep-dive into sympathetic division:
   • Locations of pre- and post-ganglionic cell bodies.
   • Signal routes, innervation targets, and effects.
   • Three pathways once a pre-ganglionic axon enters the sympathetic chain via a white ramus communicans.
   • Contrast white vs. gray rami communicantes.
   • Define sympathetic splanchnic nerves.

Page 3 – Global Nervous-System Organization

Central Nervous System (CNS)

• Components: brain and spinal cord.
• Core function: integration and command.

Peripheral Nervous System (PNS)

• Cranial and spinal nerves—communication lines between CNS and body.

PNS Sub-divisions

• Sensory (afferent) division → conducts impulses toward CNS from somatic & visceral receptors.
• Motor (efferent) division → conducts impulses from CNS to effectors.

Motor Division Branches

1. Somatic Nervous System (voluntary)
   • Target: \text{skeleton muscle}.
   • Input: exteroceptive senses (touch, hearing, sight).

2. Autonomic Nervous System (involuntary)
   • Target: cardiac muscle, smooth muscle, glands.
   • Regulates HR, digestion, respiration, salivation, perspiration, pupillary diameter, sexual arousal.

ANS Functional Dichotomy

• Sympathetic (“fight or flight”; neurotransmitter NE; adrenergic).
• Parasympathetic (“rest & digest”; neurotransmitter ACh; cholinergic).

Page 4 – SNS vs. ANS Framework

Page 5 – Comparative Circuitry Diagram (Tortora Fig 15.01)

• Somatic: single myelinated axon from spinal cord to skeletal muscle; releases ACh.
• Sympathetic: short myelinated pre-ganglionic axon → autonomic ganglion → long unmyelinated post-ganglionic axon → visceral effectors (or adrenal medulla).
• Adrenal medulla pathway: chromaffin cells act as post-ganglionic neurons releasing circulating Epi/NE.
• Parasympathetic: long myelinated pre-ganglionic axon → terminal ganglion → short unmyelinated post-ganglionic axon.

Page 6 & 7 – Two Divisions Recap

• Parasympathetic = routine maintenance (“Rest & Digest”).
• Sympathetic = rapid mobilization (“Fight, Flight, Fright”).
• Antagonistic yet complementary balance (“yin-yang”).

Page 8 – Structural Comparison

Sympathetic (Thoracolumbar)
• Presynaptic origin: T1-L2 lateral horn.
• Pre-ganglionic length: short.
• Post-ganglionic length: long.
• Ganglia near spinal cord: sympathetic chain & pre-vertebral (collateral) ganglia.

Parasympathetic (Craniosacral)
• Presynaptic origin: brainstem nuclei of CN III, VII, IX, X; spinal segments S2-S4.
• Pre-ganglionic length: long.
• Post-ganglionic length: short.
• Ganglia in/near target organs (terminal or intramural).

Page 9 – Broad Anatomical Map

• Detailed charting of sympathetic and parasympathetic outflow to head, thorax, abdomen, pelvis.
• Key cranial parasympathetic ganglia: Ciliary, Pterygopalatine, Submandibular, Otic.
• Sympathetic chain extends cervical → coccygeal; each ganglion projects to dermatomal skin & visceral branches.
• Pre-vertebral sympathetic ganglia: Celiac, Aorticorenal, Superior Mesenteric, Inferior Mesenteric, Hypogastric plexus.

Page 10 – Parasympathetic Functional Themes

• Exclusively innervates internal organs (no skin or peripheral vasculature).
• General effect: inhibitory or dampening (except it stimulates digestion).

Page 11 – Parasympathetic: Anatomical Logistics

• Pre-ganglionic cell bodies:
– Brainstem nuclei for CN III (Edinger-Westphal), VII (Superior Salivatory), IX (Inferior Salivatory), X (Dorsal Motor & Nucleus Ambiguus).
– Spinal cord segments S2-S4 (intermediate gray).
• Synapse site: terminal ganglia.
– Named ganglia (head/neck).
– Intramural ganglia embedded in target organ walls.

Page 12–13 – Cranial Outflow Details

• CN III (Oculomotor) → Ciliary ganglion → sphincter pupillae & ciliary muscle (accommodation).
• CN VII (Facial) →
– Pterygopalatine ganglion → lacrimal gland, nasal mucosa.
– Submandibular ganglion → submandibular & sublingual salivary glands.
• CN IX (Glossopharyngeal) → Otic ganglion → parotid gland.
• CN X (Vagus) → extensive thoraco-abdominal distribution: heart, lungs, liver, gallbladder, stomach, pancreas, small intestine, proximal \tfrac{1}{2} of large intestine.

Page 14–15 – Sacral Outflow

• Pre-ganglionic neurons at S2-S4 travel via ventral roots → spinal nerves → ventral rami → exit as pelvic splanchnic nerves.
• Pelvic splanchnic nerves (= ONLY parasympathetic splanchnics) synapse in intramural ganglia.
• Post-ganglionic fibers → distal \tfrac{1}{2} of large intestine, urinary bladder, ureters, reproductive organs (uterus, prostate, erectile tissues).

Page 16 – Sympathetic Functional Themes

• More diffuse/widespread due to adrenal medulla and body-wide vasomotor tone.
• Accelerates most processes except digestion.

Page 17 – Sympathetic Anatomy Review

• Pre-ganglionic cell bodies: lateral horn (intermediolateral cell column) of T1-L2.
• Synapse locations:
– Paravertebral (sympathetic chain) ganglia.
– Pre-vertebral (collateral) ganglia on abdominal aorta.

Page 18 – Spinal-Cord Gray-Matter Diagram

• Clarifies four functional neuron types in gray matter: Somatic Sensory (SS), Visceral Sensory (VS), Visceral Motor (VM), Somatic Motor (SM).
• Intermediate (lateral) horn houses VM (sympathetic) cells.

Page 19 – Sympathetic Chain (Trunk)

• Paired chains lateral to vertebral column from skull base to coccyx.
• Paravertebral ganglia linked to spinal nerves via rami communicantes.

Page 20 – White vs. Gray Rami Communicantes

• White ramus communicans:
– Carries pre-ganglionic sympathetic fibers (myelinated) from spinal nerve to chain.
– Present only at T1-L2 levels.
• Gray ramus communicans:
– Carries post-ganglionic fibers (unmyelinated) from chain back to spinal nerve.
– Present at every spinal level C1-Co.

Page 21 – Thoracolumbar Outflow Route

• Sequence: lateral horn → ventral root → spinal nerve → white ramus → chain ganglion.
• Subsequent options covered next.

Page 22 – Three Sympathetic Pathways

1. Synapse at same-level paravertebral ganglion.

2. Ascend/descend within chain, synapse at different-level paravertebral ganglion.

3. Pass through chain without synapsing → emerge as splanchnic nerves → synapse in pre-vertebral ganglia.

Page 23 – Pathway 1 (Same Level)

• Fiber enters via white ramus, synapses immediately.
• Post-ganglionic exits via gray ramus → re-enters spinal nerve → targets sweat glands, arrector pili, peripheral blood vessels, visceral organs above diaphragm.

Page 24 – Pathway 2 (Different Level)

• Fiber enters chain, ascends (to cervical) or descends (to lumbar/sacral) before synapsing.
• Post-ganglionic exits via gray ramus.
• Provides sympathetic supply to head, neck, thorax, lower limbs.

Page 25 – Pathway 3 (Splanchnic Route)

• Pre-ganglionic fibers exit chain as thoracic, lumbar, or sacral splanchnic nerves (EXCEPT pelvic splanchnics which are parasympathetic).
• Synapse in pre-vertebral ganglia (celiac, superior/inferior mesenteric, aorticorenal, hypogastric).
• Post-ganglionic fibers follow arterial plexuses to abdominal & pelvic viscera.

Page 26 – Pre-vertebral (Collateral) Ganglia

• Clustered around branches of abdominal aorta.
• Major ganglia & plexuses:
– Celiac.
– Aorticorenal.
– Superior Mesenteric.
– Inferior Mesenteric.
– Hypogastric plexus.
• Serve midline organs independent of sympathetic chain length.

Page 27 – Adrenal Medulla

• Post-ganglionic sympathetic neurons that lost axons but retained secretory capability.
• Release \approx 80\% epinephrine, 20\% norepinephrine into blood → prolonged sympathetic-like effects (e.g., prolonged HR, BP, BG rise).
• Acts as a “neuroendocrine amplifier” of sympathetic response.

Page 28 – Summary of Physiologic Effects

• Sympathetic: pupil dilation, bronchodilation, positive chronotropy/inotropy, vasoconstriction skin/GI, glycogenolysis, ejaculation, piloerection, sweating, decreased peristalsis.
• Parasympathetic: pupil constriction, salivation, bronchoconstriction, negative chronotropy, increased GI motility & secretion, bile release, micturition, erection.

Page 29 – Head-to-Head Cheat-Sheet

Sympathetic
• Origin: T1-L2 lateral horn.
• Abdominal entry: thoracic & lumbar splanchnics.
• Synapse: celiac, superior & inferior mesenteric ganglia.
• Key effects: \uparrow HR, \uparrow BP, \uparrow airway diameter, \downarrow digestion, ejaculation.

Parasympathetic
• Origin: CN III, VII, IX, X + S2-S4.
• Abdominal entry: Vagus (foregut & midgut) + pelvic splanchnics (hindgut).
• Synapse: intramural ganglia.
• Key effects: \downarrow HR, bronchoconstriction, \uparrow digestion, erection.

Page 30 – Visceral Sensory System

• Visceral afferents share dorsal roots with somatic afferents.
• Leads to referred pain: visceral pain perceived in somatic dermatomes because CNS misinterprets convergent signals.

Page 31–32 – Referred Pain Examples

• Myocardial infarction → pain in left chest/arm (C8–T2 dermatomes).
• Appendicitis → initial peri-umbilical pain (T10 dermatome) shifting to right lower quadrant.

Page 33 – Closing Slide / Questions

• Reinforces theme: sympathetic = stress, parasympathetic = peace.
• Encouraged review of antagonistic yet balanced responses.