Overview of Cranial Nerves

Introduction

• Brief overview of cranial nerves
• Discussion points: origin, structures supplied, fibers, functions, sensory/motor, clinical anatomy, skull foramen

Olfactory Nerve (Cranial Nerve I)

• Origin: Roof of nasal cavity (olfactory mucosa)
• Structures Supplied: Nasal cavity
• Fibers: Special visceral afferent (SVA) fibers
• Function: Smell (olfaction)
• Sensory/Motor: Sensory
• Skull Foramen: Olfactory foramina of the cribriform plate (ethmoid bone)

Optic Nerve (Cranial Nerve II)

• Origin: Retina (ganglion cells)
• Structures Supplied: Photoreceptors (rods, cones)
• Fibers: Special sensory afferent fibers
• Function: Vision
• Sensory/Motor: Sensory
• Skull Foramen: Optic canal
• Pathway: Optic chiasma → Lateral geniculate nucleus → Occipital lobe (primary visual cortex)

Oculomotor Nerve (Cranial Nerve III)

• Origin: Midbrain (level of superior colliculus)
• Structures Supplied: Superior rectus, levator palpebrae superioris, inferior rectus, inferior oblique, medial rectus, pupil (sphincter pupillae), ciliary muscle
• Fibers: General somatic efferent (GSE) and General visceral efferent (GVE)
• Function: Eye movement, eyelid movement, accommodation, pupil constriction
• Sensory/Motor: Motor
• Skull Foramen: Superior orbital fissure

Trochlear Nerve (Cranial Nerve IV)

• Origin: Midbrain (level of inferior colliculus)
• Structures Supplied: Superior oblique muscle
• Fibers: General somatic efferent (GSE)
• Function: Eye movement (depresses and laterally rotates)
• Sensory/Motor: Motor
• Skull Foramen: Superior orbital fissure

Trigeminal Nerve (Cranial Nerve V)

• Origin: Pons, trigeminal ganglion, various nuclei (midbrain, pons, medulla)
• Structures Supplied: Skin of scalp, eyelids, conjunctiva, external ear, jaw, chin, nose, nasal and oral cavities, muscles of mastication (e.g., masseter), tensor tympani, tensor veli palatini
• Fibers: Special visceral efferent (SVE), General somatic afferent (GSA)
• Functions: Touch, pain, temperature, mastication
• Sensory/Motor: Both
• Branches & Skull Foramina: V1 - Ophthalmic (Superior orbital fissure) | V2 - Maxillary (Foramen rotundum) | V3 - Mandibular (Foramen ovale)

Abducens Nerve (Cranial Nerve VI)

• Origin: Inferior pons (level of facial colliculus)
• Structures Supplied: Lateral rectus muscle
• Fibers: General somatic efferent (GSE)
• Function: Eye movement (lateral rotation)
• Sensory/Motor: Motor
• Skull Foramen: Superior orbital fissure

Facial Nerve (Cranial Nerve VII)

• Origin: Pons
• Structures Supplied: Muscles of facial expression, stapedius, lacrimal glands, nasal glands, Palatine glands, anterior 2/3 of tongue (taste), ear
• Fibers: Special visceral efferent (SVE), General visceral efferent (GVE), Special visceral afferent (SVA), General somatic afferent (GSA)
• Functions: Facial expression, lacrimation, nasal secretion, taste, touch pain, temperature
• Sensory/Motor: Both
• Skull Foramen: Internal acoustic meatus, Stylomastoid foramen

Vestibulocochlear Nerve (Cranial Nerve VIII)

• Origin: Pons-medulla junction
• Structures Supplied: Vestibule (macula), semicircular canals (crista ampullaris), cochlea (cochlear duct, spiral organ of Corti)
• Fibers: Special sensory afferent (SSA), some efferent
• Functions: Balance (static and dynamic equilibrium), hearing
• Sensory/Motor: Both (primarily sensory)
• Skull Foramen: Internal acoustic meatus

Glossopharyngeal Nerve (Cranial Nerve IX)

• Origin: Medulla
• Structures Supplied: Stylopharyngeus muscle, pharynx, soft palate, tonsils, posterior 1/3 of tongue, ear, carotid sinus and bodies, parotid gland
• Fibers: Special visceral efferent (SVE), General visceral afferent (GVA), General somatic afferent (GSA), General visceral efferent (GVE), Special visceral afferent (SVA)
• Functions: Elevate pharynx, touch pain temperature, taste, regulation of BP/Oxygen/CO2
• Sensory/Motor: Both
• Skull Foramen: Jugular foramen

Vagus Nerve (Cranial Nerve X)

• Origin: Medulla
• Structures Supplied: Pharynx, larynx, heart, thoracic and abdominal viscera, epiglottis (taste), ear
• Fibers: General visceral efferent (GVE), Special visceral afferent (SVA), General somatic afferent (GSA), Special visceral efferent (SVE), General visceral afferent (GVA)
• Functions: Main parasympathetic nerve, balance, taste, heart rate regulation, secretion of glands
• Sensory/Motor: Both
• Skull Foramen: Jugular foramen

Accessory Nerve (Cranial Nerve XI)

• Origin: Medulla (cranial part), Cervical spinal cord (spinal part)
• Structures Supplied: Sternocleidomastoid (SCM), trapezius, some vagal components
• Fibers: General somatic efferent (GSE), some special visceral efferent (SVE)
• Functions: Neck flexion, lateral flexion, contralateral head rotation, elevates and retracts scapula
• Sensory/Motor: Motor
• Skull Foramen: Jugular foramen (cranial), Foramen magnum (spinal)

Hypoglossal Nerve (Cranial Nerve XII)

• Origin: Medulla
• Structures Supplied: Intrinsic and extrinsic muscles of the tongue
• Fibers: General somatic efferent (GSE)
• Functions: Shape changes, protraction, retraction, elevation, depression of tongue
• Sensory/Motor: Motor
• Skull Foramen: Hypoglossal canal

Conclusion

• A detailed review of all cranial nerves
• Importance of understanding anatomy and functions of cranial nerves for clinical applications
• Tips for remembering different nerves and their functions

Acronym for Extraocular Muscles

• LR6 SO4 AO3:
  • LR6: Lateral Rectus - CN VI
  • SO4: Superior Oblique - CN IV
  • AO3: All Others - CN III
• Eye muscles orientation and functioning explained

Final Thoughts

• Understanding each nerve's pathway, origin, and function is crucial
• Recap and appreciation for the detailed study