12: Cranial Nerves

cranial nerve 1

olfactory

cranial nerve 2

optic nerve

cranial nerve 3

oculomotor nerve

cranial nerve 4

trochlear nerve

cranial nerve 5

trigeminal nerve

cranial nerve 6

abducens nerve

cranial nerve 7

facial nerve

cranial nerve 8

vestibulo-cochlear

cranial nerve 9

glossopharyngeal nerve

cranial nerve 10

vagus nerve

cranial nerve 11

accessory nerve

cranial nerve 12

hypoglossal

functional components of olfactory nerve

SVA → olfaction, taste, conveys input from olfactory receptors about odorants in the nasal cavity

supporting cells for olfactory nerve

similar to glia, provide nutrition to receptor cells and produce mucus

basal cells for olfactory nerve

replenish olfactory receptor cells every 1-2 cells

olfactory nerve fibers

connect olfactory receptor cells with Mitral cells

second order olfactory neurons in the Glomeruli, which or through cribiform plate of the bone

information progression in olfactory nerve

odorant molecules dissolve in the mucus and stimulate olfactory receptors located in cilia of the olfactory receptor cells (olfactory sensory neurons). the olfactory receptor cells’ axons make up the olfactory nerve. signals from olfactory receptor neurons are relayed to 2nd order olfactory neyrons (mital cells) in the olfactory bulb and makes synapses with olfactory glomeruli.

common issues with the olfactory nerve

commonly lesioned by viral infections, stem cell disruptions, and chronic inflammation in the epithelium

label with: olfactory bulb, 2nd order olfactory neurons, olfactory tract, olfactory glomeruli, cribiform plate, olfactory receptor cells

label with: olfactory nerve fibers, olfactory receptor cells, olfactory receptors (in the cilia), odor molecules, basal cells

label with: olfactory bulb (cell bodies of secondary sensory neurons - glomeruli), olfactory tract, uncus, amygdala, entorhinal area

olfactory bulb and olfactory tract

bulb: cell bodies of secondary sensory neurons (glomeruli)

tract: connects olfactory blub to primary olfactory areas. no thalamic relay nuclei for olfactory sensation. connected to limbic system, mediates emotional response to smell

primary olfactory areas that receive and process olfactory input to generate sense of smell

uncus/olfactory cortex, amygdala, entorhinal area

functional components of optic nerve

SSA → vision, hearing, balance (head only)

progression of info in optic nerve

optic nerve formed by axons from retina ganglion cells (RGCs) projecting out of eye toward lateral geniculate nucleus (LGN) in thalamus. from LGN, a second neuron projects to primary visual cortex through the internal capsule

eye → optic nerve → optic chiasm → optic tract → LGN

transection of optic nerve results in

loss of vision in the eye on the side of the lesion → loss of monocular field on same side as lesion

transection of optic tract results in

loss of visual hemifield contralateral to side of the lesion

transection AT optic chiasm results in

crossing fibers from both nasal retinas are damaged, results in loss of monocular fields of view (loss of peripheral vision)

eye movements rely on which cranial nerves

III (oculomotor), IV (trochlear), VI (abducens)

explain partial cross of fibers at optic chiasm

optic nerves carry information from both visual hemifields (ex: outer L, inner R). optic tracts carry all information from one hemifield (ex, inner and outer L). at the optic chiasm, fibers from the nasal retina cross to the contralateral side. this results in left hemifield information appearing in the right visual cortex and vice versa.

where is optic nerve

where is olfactory nerve

label binocular, left, right fields of vision; optic chiasm, optic nerves, optic tracts

tracts would extend under the nerves, with only red on the left (right hemifield) and blue on the right (left hemifield)

label with: optic chiasm, primary visual cortex, lateral geniculate body, caudal IC (fibers from LGN → visual cortex), optic tract, optic nerve

what components make up optic nerve nasal and outer sides?

outer is from ipsilateral tract, inner/nasal is from contralateral tract

where is oculomotor nerve

oculomotor functional components

GSE and GVE

GSE component of oculomotor nerve

fibers from III provide innervation to 4 of 6 extraocular muscles and muscle that raises upper eyelid; nerve innervates muscles in ipsilateral eye

which muscles does the oculomotor nerve innervate

extraocular (all ipsilateral)

• inferior rectus

• inferior oblique

• medial rectus

• superior rectus

levator palpebrae superior (raises upper eyelid)

how does superior rectus muscle move eye

moves up, and assists with inward rotation/intorsion towards nose

how does medial rectus muscle move eye

inwards/towards nose, called adduct

how does inferior rectus muscle move eye

moves down, assists with moving inwards

how does inferior oblique muscle move eye

rotates top of eye outward (extorsion) while helping elevate and move eye outward

label superior rectus, superior oblique, medial rectus, lateral rectus, inferior rectus, and inferior oblique muscles

what are the 4 directions of eye movement

upwards = elevation

downwards = depression

outwards (away from nose) = adduction

inwards (towards nose) = abduction

GVE component of oculomotor nerve

fibers innervating edinger-westphal nuc provide parasympathetic innervation of pupillary sphincter (which is the iris muscle for constriction of the pupil) and ciliary muscles (for accomodation of the lens - focus)

which cranial nerve nuclei are associated with oculomotor nerve

oculomotor (GSE)

edinger-westphal (GVE)

exploration of oculomotor nerve allows evaluation of…

status of rostral midbrain, specifically ventral and medial region

label oculomotor nucleus, oculomotor nerve

where is the trochlear nerve

functional components of trochlear nerve

GSE → carries fibers from trochlear nuclei, which innervate superior oblique muscle

how does superior oblique muscle move eye, assoc w which cranial nerve

IV (trochlear); rotates eye outwards and downwards → laterally, depression

trochlear nerve palsy

incorrect function of superior oblique muscle; eyes tilt up and in, which is the opposite of typical movement of down and out

only nerve that exists brainstem through dorsal surface is

IV, trochlear nerve

shortest cranial nerve

I, olfactory

exploration of the trochlear nerve allows evaluation of

status of caudal midbrain, specifically dorsal and medial region

label trochlear nerve, nucleus

which cranial nerve nuclei are associated with trochlear nerve

trochlear, GSE

where is abducens nerve

functional components of abducens nerve

GSE: controls lateral rectus muscle of the eye

how does lateral rectus muscle move the eye, what nerve is it assoc w

VI, abducens; moves eye outwards/away from nose/adduct

is abducens innervation ipsi or contralateral

ipsilateral only

abducens palsy

pull from medial rectus isn’t balanced by the lateral rectus

ex: in the right eye → left eye is normal and can look outwards, right eye is affected and can’t look outwards

exploration of the abducens nerve allows evaluation of

status of the pons, specifically ventral and medial regions

which cranial nerve nuclei are associated with abducens nerve

abducens, GSE

label lateral rectus and abducens nucleus

where is trigeminal nerve

functional components of trigeminal nerve

GSA

SVE

GSA in trigeminal nerve

sensitivity from most of the face/head → touch, pressure, temp, pain sensation from skin of face (exteroception), musculoskeletal sensitivity (proprioception)

SVE in trigeminal nerve

chewing muscles and some of the larynx muscles

most neurons located in the motor nucleus of the trigeminal

motor fibers go into nerve together with sensory fibers in the V3/mandibular branch (only branch with motor component)

3 nerves that trigeminal nerve innervates/splits into

opthalmic nerve (VI branch)

maxillary nerve (V2 branch)

mandibular nerve (V3 branch)

trigeminal VI branch - opthalmic nerve

skin of forehead, upper eyelids, lateral aspects of nose

input to spinal nucleus of trigeminal nucleus

trigeminal V2 branch - maxillary nerve

lower eyelids and cheeks

input to principal sensory nucleus of V

trigeminal V3 branch - mandibular nerve

lateral scalp, skin anterior to ear, lower cheeks, lips

input to mesenphalic nucleus of trigeminal nucleus

what trigeminal branch(es) has motor component

V3/mandibular only

which regions are innervated by which trigeminal branch

which cranial nerve nuclei are associated with trigeminal nerve

trigeminal sensory nucleus (mesencephalic, principal, and spinal regions), GSA

trigeminal motor nucleus, SVE

where is facial nerve

functional components of facial nerve

SVE

GVE

SVA

GSA

SVE in facial nerve

banchial motor nerve

• innervation of muscles of facial expression, stylohyoid, stapedius → fibers from facial motor nucleus

GVE in facial nerve

visceral motor nerve

• innervation of lacrimal, submandibular salivary, submandibular salivary glands

  • preganglionic neurons in superior salivary nucleus

  • postganglionic neurons in pterygopalatine ganglia and submandibular ganglia

these are parasympathetic innervations of the salivary glands!!

SVA in facial nerve

special sensory nerve

• receives taste to anterior 2/3 of tongue (solitary nucleus)

GSA in facial nerve

general sensory

• receives touch, pressure, temperature, pain sensitive from external ear area (spinal trigeminal nucleus)

which are branchial, visceral, special sensory, and general sensory branches?

which cranial nerve nuclei are associated with facial nerve

superior salivatory

facial motor

solitary nucleus

spinal/trigeminal

facial expression muscles rare controlled by…

bilateral descending projections from the cortex

• upper facial muscles

contralateral descending projections from the cortex

• lower facial muscles

lesion in cortical fibers controlling facial motor nucleus causes…

contralateral paralysis in lower half of the face

lesion in facial nerve causes…

paralysis of the ipsilateral half of the face (ipsilateral to lesioned nerve)

Bell’s palsy

facial nerve lower motor neuron lesion (LMNL)

where is vestibulo-cochlear nerve

functional components of vestibulo-ocular nerve

SSA

components of SSA in vestibulo-ocular nerve

auditory component

vestibular component

auditory component of VIII

cochlear nerve → primary sensory neurons located in the spiral (cochlear) ganglion), brings auditory signals to the cochlear nuclei

vestibular component of VIII

vestibular nerve → primary sensory neurons located in scarpa (vestibular) ganglion, brings auditory signals to vestibular nuclei

label VIII vestibular component, VIII auditory component, organ of corti (spiral), spiral ganglion

vestibulo-ocular connections and reflex function

mechanism to maintain focused gaze (in same spot) while head or body is moving/in an unstable environment

how does VOR (vestibulo-ocular reflex) work

elicits compensatory eye movements in opposite direction of head movements to stabilize gaze on a fixed point, stabilizes images in retina

cranial nerves involved in VOR

sensory info from vestibular system → nucleus controlling eye movement to adjust eye position: III, IV, VI (oculomotor, trochlear, abducens)

• coordinates sensory input from vestibular nuclei with the activity of extraocular muscles to correct eye position

how to mimic compensatory eye movement using water?

COWS: cold opposite warm same

• cold water into an ear mimics head turn to opposite side; eyes slowly move SAME way to compensate, then Nystagmus (fast correction movement to original side) (mimics contralateral head turn)

• warm water into an ear mimics head turn to same side; expect compensatory movement to OPPOSITE side (mimics ipsilateral head turn)

two general steps of COWS movement

1) slow phase correctional movement

2) Nystagmus → eyes snap back to center/toward stimulated ear