Week 5 · Lecture Slides · Nervous System

PNS & Autonomic.

Seven slides on the peripheral nervous system: 12 cranial nerves, 31 spinal nerves, somatic vs autonomic, and the sympathetic vs parasympathetic split. Sketch each system from memory.

Practice these cards

Core concept

PNS & Autonomic Nervous System

What you'll do

  • Move through six concept slides
  • Three slides have a drawable canvas
  • Toolbar: pen color, size, eraser, undo, add image, save
  • Drop in your own anatomy images to label them
PNS: In and Out of CNS

Sensory in

Cranial nerve sensors
Spinal nerve sensors
Dorsal root ganglia

Motor out

Somatic: voluntary, skeletal
Autonomic: sympathetic + parasympathetic
Enteric (gut)

Definition

PNS Overview

Everything outside CNS

  • Nerves: bundles of axons (PNS) vs tracts (CNS)
  • Ganglia (PNS) vs nuclei (CNS)
  • 12 cranial nerves from brain
  • 31 spinal nerves from cord (8C + 12T + 5L + 5S + 1Co)
  • Sensory (afferent) in, motor (efferent) out
  • Glia: Schwann cells (myelin), satellite cells (ganglia)
Takeaway: PNS connects the CNS to everything else. Sensors send info in, motor commands go out. The same vocabulary changes name across the CNS/PNS border: tract→nerve, nucleus→ganglion.

Cranial nerves

12 Cranial Nerves

Names + functions

  • I Olfactory smell
  • II Optic vision
  • III Oculomotor most eye movements
  • IV Trochlear superior oblique
  • V Trigeminal face sensation, chewing
  • VI Abducens lateral rectus
  • VII Facial facial expression, taste anterior tongue
  • VIII Vestibulocochlear hearing + balance
  • IX Glossopharyngeal swallowing, taste posterior tongue
  • X Vagus parasympathetic to thorax/abdomen
  • XI Accessory SCM, trapezius
  • XII Hypoglossal tongue muscles
Draw: a ventral view of the brain. Number 12 nerves exiting in order from anterior (olfactory bulbs) to posterior (hypoglossal). Mnemonic for names: "On Old Olympus Towering Tops, A Finn And German Viewed Some Hops".

Somatic vs autonomic

Two Motor Divisions

Voluntary vs involuntary

  • Somatic motor skeletal muscle
  • One neuron from CNS to muscle
  • Neurotransmitter: ACh at NMJ
  • Always excitatory
  • Autonomic motor smooth/cardiac/glands
  • Two neurons: preganglionic (CNS) → postganglionic (target)
  • Synapse in autonomic ganglia
  • Can be excitatory OR inhibitory
Takeaway: the autonomic two-neuron chain lets you have ganglia outside the CNS, and lets ACh and norepinephrine combinations split sympathetic vs parasympathetic responses.

Sympathetic

Sympathetic: Fight-or-Flight

Thoracolumbar outflow

  • Thoracolumbar origin (T1-L2)
  • Short pre, long postganglionic fibers
  • Pre uses ACh, post uses norepinephrine
  • Sympathetic chain (paravertebral ganglia) alongside spinal cord
  • Splanchnic nerves to prevertebral ganglia (celiac, superior/inferior mesenteric)
  • Effects: dilate pupils, raise HR, dilate bronchi, mobilize glucose
Draw: a stick figure with arrows showing sympathetic effects on key organs. Dilate pupils (eye), raise HR (heart), dilate bronchi (lungs), reduce GI motility (gut), mobilize glucose (liver), dilate skeletal muscle vessels, constrict skin vessels.

Parasympathetic

Parasympathetic: Rest-and-Digest

Craniosacral outflow

  • Craniosacral origin (CN III, VII, IX, X + S2-S4)
  • Long pre, short postganglionic fibers
  • Both pre and post use ACh
  • Ganglia close to or in target organs
  • Vagus (X) handles thorax + most abdomen
  • Effects: constrict pupils, lower HR, increase GI motility, voiding
Draw: same body outline as before. Arrows showing parasympathetic effects: constrict pupils, lower HR, constrict bronchi, increase GI motility + secretion, empty bladder, achieve erection. The two systems are antagonistic at most targets.

Clinical

When the PNS Fails

Diseases and drugs

  • Bell palsy CN VII palsy, one-sided facial droop
  • Trigeminal neuralgia CN V pain
  • Carpal tunnel median nerve compression at wrist
  • Diabetic neuropathy distal symmetric, stocking-glove
  • Horner syndrome sympathetic damage: ptosis, miosis, anhidrosis
  • Atropine blocks muscarinic ACh, dilates pupils, raises HR (parasympatholytic)
  • Beta blockers block sympathetic effects on heart
Takeaway: autonomic pharmacology is one of the highest-yield clinical topics. Sympathetic (adrenergic) drugs map to α1, α2, β1, β2 receptors. Parasympathetic (cholinergic) drugs map to muscarinic vs nicotinic receptors.