Understanding the Parasympathetic Nervous System

Sep 11, 2024

Crash Course: Anatomy & Physiology - Parasympathetic Nervous System

Introduction

  • Heart beats at 60 beats per minute at rest.
  • Disconnecting the heart from the autonomic nervous system increases heartbeat to around 100 bpm.
  • Heart and body balance maintained by the parasympathetic nervous system.

Parasympathetic Nervous System

  • Known as the calming system of the autonomic nervous system.
  • Handles digestion, reproduction, excretion, and immune response.
  • Functions between excitement and inhibition to maintain bodily balance.

Sympathetic vs Parasympathetic

  • Sympathetic system responds to immediate stress.
  • Parasympathetic system manages ongoing bodily functions.
  • Different ganglia locations: sympathetic (near spinal cord), parasympathetic (near effectors).
  • Neurotransmitter use differs: both use ACh preganglionic; parasympathetic also uses ACh postganglionic, sympathetic uses norepinephrine.

Anatomical Differences

  • Sympathetic nerves originate from the thoracolumbar area.
  • Parasympathetic nerves are craniosacral and mostly bypass the spinal cord.
  • Cranial nerves can be autonomic, voluntary motor, or sensory.

The 12 Cranial Nerves

  • Olfactory (I): Scent to brain.
  • Optic (II): Visual data to brain.
  • Oculomotor (III): Controls eye movements.
  • Trochlear (IV): Controls single eye muscle.
  • Trigeminal (V): Innervates face/jaw.
  • Abducens (VI): Eye side-to-side movement.
  • Facial (VII): Facial expressions.
  • Auditory (VIII): Hearing.
  • Glossopharyngeal (IX): Tongue and pharynx.
  • Vagus (X): Extensive nerve, important for visceral organ communication.
  • Spinal Accessory (XI): Moves head/shoulders.
  • Hypoglossal (XII): Swallowing, talking.

Mnemonics for Remembering Cranial Nerves

  • Example: "On old Olympus’ towering top, a Fin and German viewed some hops."
  • Another: "Onward old orcs! Toward the Argonath for a Great Villain! Slay Hobbits!"

Functions of Cranial Nerves (Sensory, Motor or Both)

  • Mnemonic: "Some say marry money, but my brother says big brains matter more."

The Vagus Nerve

  • Connects brainstem to visceral organs.
  • Sensory and motor functions, crucial for parasympathetic response.
  • Helps manage stress, relax after a stressful day, and regulate heart rate.

Balance between Sympathetic and Parasympathetic

  • Homeostasis is key to life, with both systems balancing each other.
  • Sympathetic tone vs. parasympathetic tone.
  • Balance is crucial for activities such as eating and sexual function.

Conclusion

  • Reviewed parasympathetic nervous system and cranial nerves.
  • Highlighted the importance of the vagus nerve.

Credits

  • Contributors: Headmaster of Learning Thomas Frank, co-sponsors Jennifer K. Koons, Tim Wisard, Mich Acosta.
  • Filming location: Dr. Cheryl C. Kinney Crash Course Studio.
  • Team: Kathleen Yale (writer), Blake de Pastino (editor), Dr. Brandon Jackson (consultant), Nicholas Jenkins (director), Nicole Sweeney (script supervisor/editor), Michael Aranda (sound designer), Thought Café (graphics).