Lecture Notes: Cranial Nerves and Their Functions

Olfactory Nerve (CN I)

• Function: Transmits smell information to the brain.
• Origin: Olfactory epithelium in the nasal cavity.
• Pathway:
  • Axons form bundles called Fila.
  • Pass through CRI plate in the ethmoid bone.
  • Connect to olfactory bulb, then to olfactory cortex.
• Damage: Can lead to anosmia or impaired smell. Causes include head trauma, tumors.

Optic Nerve (CN II)

• Function: Transmits visual information to the brain.
• Origin: Retina, composed of retinal ganglion cell axons.
• Pathway:
  • Axons form the optic nerve, exit at optic disc.
  • Meet at optic chiasm, fibers cross.
  • Continue as optic tract to lateral geniculate nucleus.
• Damage: Results in visual defects depending on location, e.g., blindness, loss of visual fields.

Oculomotor Nerve (CN III)

• Function: Controls most eye movements and pupil constriction.
• Muscles Supplied: Medial rectus, superior rectus, inferior rectus, inferior oblique, levator palpebrae superioris.
• Damage: Causes eye deviation, ptosis, dilated pupil, and impaired focus.

Trochlear Nerve (CN IV)

• Function: Controls superior oblique muscle for down-and-out eye movement.
• Unique Features: Only cranial nerve to exit from the back of the brainstem.
• Damage: Causes upward eye deviation, diplopia.

Trigeminal Nerve (CN V)

• Function: Main sensory nerve of the head; controls muscles for chewing.
• Divisions: Ophthalmic, maxillary, mandibular.
• Nuclei: Main sensory, spinal trigeminal, mesencephalic, and motor.
• Damage: Causes facial pain, abnormal sensation, trigeminal neuralgia.

Abducens Nerve (CN VI)

• Function: Controls lateral rectus muscle for lateral eye movement.
• Pathway: Originates in the pons, part of the medial longitudinal fasciculus.
• Damage: Causes esotropia and diplopia.

Facial Nerve (CN VII)

• Function: Controls facial expression muscles; taste sensation; salivary and lacrimal glands.
• Nuclei: Facial motor, superior salivatory, nucleus of the solitary tract.
• Damage: Leads to facial paralysis, Bell's palsy, impaired taste.

Vestibulocochlear Nerve (CN VIII)

• Components: Vestibular (balance) and cochlear (hearing).
• Pathway: Cochlear nerve connects hair cells to cochlear nuclei; vestibular connects to vestibular nuclei.
• Damage: Causes hearing loss, tinnitus, balance issues.

Glossopharyngeal Nerve (CN IX)

• Function: Sensory and motor functions related to tongue and throat.
• Nuclei: Nucleus ambiguus, nucleus solitarius, spinal trigeminal nucleus.
• Damage: Causes loss of taste, swallowing issues, glossopharyngeal neuralgia.

Vagus Nerve (CN X)

• Function: Extends from brainstem to colon; controls numerous muscles and sensory information.
• Unique Role: Major parasympathetic nerve.
• Damage: Causes hoarseness, swallowing difficulty, heart rate abnormalities.

Accessory Nerve (CN XI)

• Function: Controls sternocleidomastoid and trapezius muscles.
• Pathway: Divided into spinal and cranial components.
• Damage: Causes weakness in shoulder/neck movements, winged scapula.

Hypoglossal Nerve (CN XII)

• Function: Controls tongue muscles.
• Pathway: From hypoglossal nuclei in the medulla to the tongue.
• Damage: Causes tongue weakness, atrophy, difficulty with speech/swallowing.