Lecture on the Parasympathetic Nervous System

Introduction

• Average heart rate at rest: ~60 beats per minute
• Disconnecting heart from autonomic system: heart increases to ~100 beats per minute
• Roles of the Parasympathetic Nervous System (PNS):
  • Calms the body
  • Regulates digestion, reproduction, excretion, and infection fighting
  • Maintains balance between excitement and inhibition

Parasympathetic vs. Sympathetic Nervous Systems

• Functions:
  • Sympathetic: handles immediate crisis
  • Parasympathetic: handles routine bodily functions
• Ganglia Locations:
  • Sympathetic: near spinal cord
  • Parasympathetic: near effectors
• Neurotransmitters:
  • Both systems use acetylcholine (ACh) in preganglionic synapses
  • Parasympathetic: also uses ACh in postganglionic synapses
  • Sympathetic: uses norepinephrine in postganglionic synapses

Anatomical Differences

• Sympathetic Nerves:
  • Origin: thoracolumbar area of spinal cord
• Parasympathetic Nerves:
  • Origin: craniosacral region (brain and near tailbone)
  • Cranial nerves: 12, with varying functions (autonomic motor, voluntary motor, sensory)

The Cranial Nerves

• Names and Functions:
  1. Olfactory Nerve (I): Smell
  2. Optic Nerve (II): Vision
  3. Oculomotor Nerve (III): Eye movements (4 muscles)
  4. Trochlear Nerve (IV): Eye movement (1 muscle)
  5. Trigeminal Nerve (V): Facial and jaw muscles
  6. Abducens Nerve (VI): Lateral eye movement
  7. Facial Nerve (VII): Facial expressions
  8. Auditory Nerve (VIII): Hearing
  9. Glossopharyngeal Nerve (IX): Tongue and pharynx
  10. Vagus Nerve (X): Visceral organs (heart, lungs, stomach)
  11. Spinal Accessory Nerve (XI): Head and shoulder movement
  12. Hypoglossal Nerve (XII): Swallowing, speech
• Mnemonics for Cranial Nerves:
  • Names: "On on Olympus' towering top, a Fin and German viewed some hops"
  • Functions: "Some say marry money, but my brother says big brains matter more"

Vagus Nerve (X)

• Extensive: brainstem to visceral organs
• Functions:
  • Sensory: signals from peripheral system to brain
  • Motor: brain signals to body

Homeostasis and Sympathetic Tone

• Balance:
  • Parasympathetic allows routine functions
  • Sympathetic handles emergencies
• Example:
  • Stress increases sympathetic activity
  • Relaxation increases parasympathetic responses

Role in Reproduction

• Parasympathetic: calms, enables sexual function
• Sympathetic: excites, maintains arousal
• Conclusion: Balance between both systems essential for sex and other functions

Summary

• Discussed PNS's structural differences, 12 cranial nerves
• Emphasis on vagus nerve’s role in parasympathetic responses and homeostasis

Credits

• Written by Kathleen Yale
• Edited by Blake de Pastino
• Consultant: Dr. Brandon Jackson
• Directed by Nicholas Jenkins
• Script supervisor and editor: Nicole Sweeney
• Sound designer: Michael Aranda
• Graphics team: Thought Café