Overview of Cranial Nerves

Introduction

• Brief overview and recap of cranial nerves.
• Discusses each nerve individually: origin, supplied structures, fiber types, functions, and clinical anatomy.
• Includes sensory, motor, or both; pathways through skull holes.

Cranial Nerve I: Olfactory Nerve

• Origin: Roof of nasal cavity (olfactory mucosa).
• Supplied Structures: Nasal cavity.
• Fibers: Special visceral afferent (SVA) fibers.
• Function: Smell (olfaction).
• Nature: Sensory nerve.
• Pathway: Through olfactory foramina in the cribriform plate of the ethmoid bone to olfactory bulb then olfactory tract to brain.

Cranial Nerve II: Optic Nerve

• Origin: Retina (ganglion cells, rods, cones, and melanopsin containing cells).
• Supplied Structures: Photoreceptors in retina.
• Fibers: Special sensory afferent fibers.
• Function: Vision.
• Nature: Sensory nerve.
• Pathway: Through optic canal, crosses at optic chiasma, to lateral geniculate nucleus, then occipital lobe.

Cranial Nerve III: Oculomotor Nerve

• Origin: Midbrain (level of superior colliculus).
• Supplied Structures: Superior rectus, levator palpebrae superioris, inferior rectus, inferior oblique, medial rectus, pupil (sphincter pupillae), and ciliary muscle.
• Fibers: General somatic efferent (GSE), General visceral efferent (GVE).
• Function: Eye movement, eyelid movement, accommodation (lens), pupil constriction.
• Nature: Motor nerve.
• Pathway: Through superior orbital fissure inside common tendinous ring.

Cranial Nerve IV: Trochlear Nerve

• Origin: Midbrain (level of inferior colliculus).
• Supplied Structures: Superior oblique muscle.
• Fibers: General somatic efferent (GSE).
• Function: Eye movement (depression and lateral rotation).
• Nature: Motor nerve.
• Pathway: Through superior orbital fissure outside common tendinous ring.

Cranial Nerve V: Trigeminal Nerve

• Origin: Primarily in the pons (trigeminal ganglion, several nuclei in midbrain, pons, medulla).
• Supplied Structures: Scalp, eyelids, conjunctiva, external ear, jaw, chin, nose, nasal cavity, oral cavity, tongue, orbital cavity, nasopharynx, eustachian tubes, tonsils, muscles of mastication, tensor tympani, tensor veli palatini.
• Fibers: Special visceral efferent (SVE), General somatic afferent (GSA).
• Function: Sensations (touch, pain, temperature, pressure), mastication.
• Nature: Mixed nerve.
• Pathway: Superior orbital fissure (V1), foramen rotundum (V2), foramen ovale (V3 and motor fibers).
• Divisions: Ophthalmic (V1), Maxillary (V2), Mandibular (V3).

Cranial Nerve VI: Abducens Nerve

• Origin: Pons (level of facial colliculus).
• Supplied Structures: Lateral rectus muscle.
• Fibers: General somatic efferent (GSE).
• Function: Eye movement (lateral rotation).
• Nature: Motor nerve.
• Pathway: Through superior orbital fissure inside common tendinous ring.

Extraocular Muscle Mnemonic

• LR6 SO4 AT3: Lateral rectus (CN VI), Superior oblique (CN IV), All others (CN III).
• Muscles: superior rectus, inferior rectus, inferior oblique, medial rectus, levator palpebrae superioris.

Cranial Nerve VII: Facial Nerve

• Origin: Pons (many nuclei).
• Supplied Structures: Muscles of facial expression, stapedius, digastric muscles, stylohyoid, lacrimal glands, nasal glands, palatine glands, anterior 2/3 of tongue, tympanic membrane, external ear.
• Fibers: Special visceral efferent (SVE), General visceral efferent (GVE), Special visceral afferent (SVA), General somatic afferent (GSA).
• Function: Facial expression, lacrimation, nasal secretions, taste, touch, pain, temperature from ear.
• Nature: Mixed nerve.
• Pathway: Internal acoustic meatus, stylo-mastoid foramen.

Cranial Nerve VIII: Vestibulocochlear Nerve

• Origin: Pons-medulla junction.
• Supplied Structures: Inner ear (vestibule, semicircular canals, cochlea).
• Fibers: Special sensory afferent fibers.
• Function: Balance (static and dynamic equilibrium), sound.
• Nature: Primarily sensory nerve, minor motor role.
• Pathway: Internal acoustic meatus.

Cranial Nerve IX: Glossopharyngeal Nerve

• Origin: Medulla.
• Supplied Structures: Stylopharyngeus, pharynx, soft palate, tonsils, posterior 1/3 of tongue, carotid bodies, ear, parotid gland.
• Fibers: Special visceral efferent (SVE), General visceral afferent (GVA), General somatic afferent (GSA), General visceral efferent (GVE).
• Function: Elevate pharynx, touch, pain, temperature (ear, pharynx, soft palate, tonsils, posterior tongue), taste, carotid body function.
• Nature: Mixed nerve.
• Pathway: Jugular foramen.

Cranial Nerve X: Vagus Nerve

• Origin: Medulla.
• Supplied Structures: Pharynx, larynx, heart, thoracic/abdominal viscera (stomach, esophagus, liver, etc.), epiglottis, ear.
• Fibers: General visceral efferent (GVE), Special visceral afferent (SVA), General somatic afferent (GSA), Special visceral efferent (SVE), General visceral afferent (GVA).
• Function: Main parasympathetic nerve: pharynx/larynx contraction, heart rate regulation, thoracic/abdominal viscera functions, taste (epiglottis), touch, pain, temperature (ear), carotid and aortic bodies (baroreception).
• Nature: Mixed nerve.
• Pathway: Jugular foramen.

Cranial Nerve XI: Accessory Nerve

• Origin: Medulla (cranial part), cervical spinal cord (C1-C5).
• Supplied Structures: Sternocleidomastoid, trapezius (cranial part with vagus nerve for pharynx and soft palate).
• Fibers: General somatic efferent (GSE), minor special visceral efferent (SVE).
• Function: Neck flexion, ipsilateral flexion, contralateral head rotation, scapula elevation/retraction.
• Nature: Motor nerve.
• Pathway: Jugular foramen (cranial and spinal components), foramen magnum (spinal component).

Cranial Nerve XII: Hypoglossal Nerve

• Origin: Medulla oblongata.
• Supplied Structures: Extrinsic and intrinsic muscles of the tongue.
• Fibers: General somatic efferent (GSE).
• Function: Tongue shape change, protraction, retraction, elevation, depression.
• Nature: Motor nerve.
• Pathway: Hypoglossal canal.

Conclusion

• Recap of all cranial nerves discussed.
• Thanks for following along.