Cranial Nerves & Vision

Olfactory nerve (CN I)

Function: smell

Clinical application: loss of smell (Anosmia)

Passes through the cribriform plate of the ethmoid bone

Nuclei Location: Cerebrum

Optic Nerve (CN II)

Function: vision

Clinical application: loss of sight (Anopsia)

Passes through the optic canals of the sphenoid bone

Nuclei Location: Cerebrum

Oculomotor nerve (CN III)

Function: - controls a group of muscles responsible for movements of the eyeball and eyelid (motor),

• Accommodation of the lens for near vision (parasympathetic),

• Constriction of the pupil (parasympathetic)

Clinical applications: strabismus, diplopia, and ptosis

Nuclei Location: Midbrain

strabismus

condition in which the eyes are not properly aligned with each other

diplopia

double vision

ptosis

droopy eyelid

Trochlear nerve (CN IV)

Function: controls the superior oblique muscle (involved with movement of the eyeball) (motor) - laterally

Clinical application: strabismus and diplopia

Nuclei Location: Midbrain

Trigeminal nerve (CN V)

~Three big branches~ Mixed Nerve

Function: supplies “chewing muscles” (muscles of mastication) (motor), sensation to the face (sensory)

Clinical applications: loss of muscle function and loss of facial sensation - ability to chew

Nuclei Location: Pons

Abducent nerve (CN VI)

Function: controls the lateral rectus muscle (involved with movement of the eyeball) (motor)

Clinical applications: strabismus and diplopia

Nuclei Location: Pons

Facial nerve (CN VII)

Mixed Nerve

Functions: supplies muscles of “facial expression” (motor), supplies taste to anterior 2/3 of tongue (sensory)

Clinical applications: facial (Bell’s) palsy - (right side = right CN VII) ~ paralysis

Loss of taste on anterior 2/3 of tongue

Nuclei Location: Pons

Vestibulocochlear nerve (CN VIII)

Functions: vestibular branch: equilibrium (sensory) - balance

cochlear branch: hearing (sensory)

Clinical applications: Vestibular branch: vertigo Cochlear branch: tinnitus - ringing in ears

Nuclei Location: Pons

Glossopharyngeal nerve (CN IX)

Mixed Nerve

Functions: taste on posterior 1/3 of tongue (sensory), sensation to throat (sensory), supplies muscles involved with swallowing (motor)

Clinical applications: loss of taste on posterior 1/3 of tongue, decreased sensation to throat, and difficulty swallowing

Nuclei Location: Medulla Oblongata

Vagus nerve (CN X)

Functions: sensation to throat (sensory),

• supplies muscles involved with swallowing (motor),

• carries parasympathetic information to thorax and abdomen (75%)

Clinical applications: decreased sensation to throat (“gag reflex”), difficulty swallowing, loss of parasympathetic functions in thorax and abdomen

Nuclei Location: Medulla Oblongata

Accessory nerve (CN XI)

Function: supplies the trapezius and sternocleidomastoid muscles (motor)

Clinical application: loss of muscle function

Nuclei Location: Medulla Oblongata

Hypoglossal nerve (CN XII)

Function: supplies muscles responsible for movement of tongue (motor)

Clinical applications: difficulty chewing, speaking, and swallowing

Nuclei Location: Medulla Oblongata

Smell

the olfactory nerves (CN I) are involved with this sense

only major sensation that is relayed directly to the cerebral cortex without passing through the thalamus

Taste

detected by the sensory structure of taste buds

Most taste buds are located on papillae (peg-like projections on the superior surface of the tongue)

Gustatory pathway

Gustatory pathway

when food chemicals (dissolved by saliva) come into contact with taste buds, action potentials are generated

These action potentials are sent to the thalamus by:

facial nerves (CN VII) anterior 2/3 glossopharyngeal nerve (CN IX) posterior 1/3

Vision

Accessory structures: eyelids, conjunctiva, lacrimal gland, and extrinsic eye muscles

eyelids (palpebrae)

Functions: protection, spread tears when we blink

Major Muscles: orbicularis oculi and elevator palpebrae superioris

orbicularis oculi

closes eyelid

Supplied by Facial Nerve (CN VII)

levator palpebrae superioris

opens UPPER eyelid (muscle involved with ptosis)

Supplied by Oculomotor Nerve (CN III)

lacrimal gland

produces tears

tears lubricate and cleanse the eye

superolateral

extrinsic eye muscles

Move the EYEBALL - SO₄LR₆E₃

superior rectus, inferior rectus, medial rectus, inferior oblique, superior oblique, lateral rectus

*levator palpebrae superioris move eyelid*

Superior rectus

elevates eyeball

Supplied by oculomotor nerve (CN III)

inferior rectus

depresses eyeball

supplied by oculomotor nerve (CN III)

medial rectus

moves eyeball medially

supplied by oculomotor nerve (CN III)

inferior oblique

elevates and turns eyeball laterally

supplied by oculomotor nerve (CN III)

superior oblique

depresses and turns eyeball laterally

supplied by trochlear nerve (CN IV)

lateral rectus

moves eye laterally

supplied by abducens nerve (CN VI)

cornea

anterior portion of the fibrous tunic

curved shape helps focus light rays

iris

colored portion of the eye

regulates the amount of light let into the eye

the hole in the middle is called the pupil

retina (sensory tunic)

rodes - used for black and white vision

Cones - used for Color vision

macula lutea, optic disc

macula lutea

oval region located lateral to the optic disc

contains the fovea centralis (area with the greatest visual acuity)

fovea centralis

area with the greatest visual acuity

located inside the macula lutea

optic disc

located where the retina exists the eye

“blind spot”

lens

focuses light rays on the retina

visual pathway

action potentials are carried to the thalamus by the optic nerves (CN II)

action potentials travel from the thalamus to the visual cortex