Lecture Notes: Cranial Nerves Overview

Introduction to Cranial Nerves

• Definition: 12 paired nerves originating from the brain.
• Distinct from Spinal Nerves:
  • Cranial nerves have varied functions (motor, sensory, mixed).
  • Some are not true nerves but brain projections (e.g., olfactory and optic nerves).

Names and Order of Cranial Nerves

• Mnemonic: "O-O-O to touch and feel very green vegetables. Ah."
  • Olfactory
  • Optic
  • Oculomotor
  • Trochlear
  • Trigeminal
  • Abducens
  • Facial
  • Vestibulocochlear
  • Glossopharyngeal
  • Vagus
  • Accessory
  • Hypoglossal

Origin and Pathways

• Cerebrum: Cranial nerves 1 and 2
• Midbrain: Cranial nerves 3 and 4
• Pons: Cranial nerve 5
• Pontomedullary Junction: Cranial nerves 6, 7, 8
• Medulla: Cranial nerves 9, 10, 12
• Spinal Cord: Cranial nerve 11

Embryological Development

• Involves pharyngeal arches (1, 2, 3, 4, and 6)
  • Each arch is associated with specific cranial nerves and their target structures.

Functions of Cranial Nerves

Motor and Sensory Pathways

• Motor (Efferent) Fibers: Carry signals from the brain.
  • Somatic motor: Voluntary muscle innervation.
  • Somatic branchial: Innervate muscles from branchial arches.
  • Visceral motor: Parasympathetic fibers.
• Sensory (Afferent) Fibers: Carry signals to the brain.
  • Somatic sensory: Pain, temperature, touch.
  • Visceral sensory: Information from organs.
  • Special sensory: Smell, sight, taste, hearing, balance.

Specific Nerve Functions

• Olfactory: Smell (special sensory)
• Optic: Vision (special sensory)
• Oculomotor: Eye movements, pupil constriction (motor and parasympathetic)
• Trochlear: Moves superior oblique muscle (motor)
• Trigeminal: Facial sensation, mastication (mixed)
• Abducens: Moves lateral rectus muscle (motor)
• Facial: Facial expression, taste, glandular secretions (mixed and parasympathetic)
• Vestibulocochlear: Hearing and balance (special sensory)
• Glossopharyngeal: Swallowing, taste (mixed and parasympathetic)
• Vagus: Phonation, swallowing, visceral sensory, parasympathetic control (mixed)
• Accessory: Sternocleidomastoid and trapezius muscles (motor)
• Hypoglossal: Tongue movements (motor)

Mnemonics for Function Types

• "Some say marry money, but my brother says big brains matter more."
  • M = Motor, S = Sensory, B = Both

Summary

• Cranial nerves carry diverse types of information (somatic motor, sensory, special sensory, parasympathetic).
• Nerves 3, 7, 9, and 10 are pathways for parasympathetic innervation.
• Nerves 1, 2, 7, 8, 9, and 10 carry special sensory information.