Cranial Nerves Overview

Overview

This lecture introduces the 12 cranial nerves, their functions, origins, and provides strategies and mnemonics to help remember their names and roles.

Introduction to Cranial Nerves

• Cranial nerves originate directly from the brain or brainstem.
• There are 12 paired cranial nerves, each present on both sides of the body.
• Roman numerals are used to number the cranial nerves based on their emergence from the brain (front to back).
• Cranial nerves relay information mainly between the brain and the head/neck.
• Neurons involved are afferent (sensory, to the brain) and efferent (motor, from the brain); some nerves are both.

Functions and Origins of Each Cranial Nerve

• I. Olfactory: Sensory; sense of smell; originates from cerebrum.
• II. Optic: Sensory; vision; originates from cerebrum.
• III. Oculomotor: Motor; eye movement, eyelid elevation, pupil constriction, lens accommodation; originates in midbrain.
• IV. Trochlear: Motor; eye movement; originates in midbrain.
• V. Trigeminal: Both; facial sensation, anterior 2/3 tongue sensation, muscles of mastication; originates in pons.
• VI. Abducens: Motor; lateral eye movement (abduction); originates in ponto-medullary region.
• VII. Facial: Both; facial expression, eyelid closing, taste anterior 2/3 tongue, salivation, lacrimation; originates in ponto-medullary region.
• VIII. Vestibulocochlear: Sensory; hearing and balance; originates in ponto-medullary region.
• IX. Glossopharyngeal: Both; taste and sensation posterior 1/3 tongue, pharynx sensation, swallowing, salivation; originates in medulla.
• X. Vagus: Both; sensation from ear, pharynx, larynx, thorax, abdomen; parasympathetic functions (HR↓, GI↑, sweating), swallowing, speech; originates in medulla.
• XI. Accessory: Motor; shoulder shrug, head turning; originates in medulla and cervical spinal cord.
• XII. Hypoglossal: Motor; tongue movement; originates in medulla.

Memory Aids for Cranial Nerves

• Drawing a simple face to associate nerves with facial features.
• Classic mnemonic: "On Old Olympus's Towering Top A Finn And German Viewed Some Hops" (first letter of each nerve).
• Modern mnemonic: "On Occasion Our Trusty Truck Acts Funny; Very Good Vehicle Anyhow."
• Mnemonics for function types (sensory/motor/both):
  • "Some Say Money Matters But My Brother Says Big Brains Matter More."
  • "Some Say My Mother Bought My Brother Some Bad Beer My My."

Key Terms & Definitions

• Afferent Neuron — Sensory neuron carrying signals toward the brain.
• Efferent Neuron — Motor neuron carrying signals away from the brain.
• Cerebrum — Forebrain region where nerves I and II originate.
• Pons/Medulla Oblongata — Brainstem regions where most cranial nerves originate.
• Mastication — Chewing.
• Parasympathetic Nervous System — "Rest and digest" body functions.

Action Items / Next Steps

• Practice and memorize mnemonics for cranial nerve names and functions.
• Review origins and primary functions for each cranial nerve.
• Watch for future lessons on in-depth functions and cranial nerve assessments.