Ocular Disease III - Basic Neuro

What cranial nerves have their nucleus in the midbrain?

CN III, IV

Rostral refers to?

Upper (closer to head)

Caudal refers to?

Lower (closer to the bottom)

3 parts of the brainstem?

Midbrain, pons, medulla

CN III nucleus location?

midbrain

CN IV nucleus location?

midbrain

CN IX nucleus location?

medulla

CN X nucleus location?

medulla

CN XI nucleus location?

medulla

CN XII nucleus location?

medulla

CN V nucleus location?

pons

CN VI nucleus location?

pons

CN VII nucleus location?

pons

CN VIII nucleus location?

pons

What structure looks like Mickey Mouse on the MRI?

midbrain

The midbrain is aka...

mesencephalon

What structure has the superior and inferior colliculi?

Midbrain

A lesion of the superior colliculus will affect...

saccadic eye movements and eye-head coordination

What is the basis pontis?

A large bump on the ventral surface of the pons

CN nuclei of midbrain?

III, IV

CN nuclei of pons?

V, VI, VII, VIII

CN nuclei of medulla?

IX, X, XI, XII

What is on the dorsal side of the medulla?

fourth ventricle and cerebellum

What is directly connected caudally to the medulla?

spinal cord

From superior to inferior, what is the order of the three brainstem structures?

midbrain, pons, medulla

What is Wallenberg Syndrome?

aka Dorsolateral medullary syndrome:
- Ipsilateral horner syndrome (inverse ptosis + miotic pupil)
- Contralateral hypertropia (skew deviation)
- Torsional nystagmus
- Hoarseness, difficulty swallowing (CN IX & X)
- Ataxia (since next to cerebellum)
- Cause = vertebral artery dz

What is the MLF?

Medial Longitudinal Fasciculus - bundle of fibers controlling vestibular fxn and eye movements; oculomotor, trochlear, and abducens nuclei integrated by MLF

What bundle of fibers that run along the brainstem integrate CN III, IV, and VI?

MLF

What is the riMLF?

Rostral Interstitial nucleus of the Medial Longitudinal Fasciculus - for vertical saccades, connects CN III nuclei via posterior commissure

What connects CN III to the riMLF?

Posterior commissure

The MLF extends from ___ to ___.

rostral midbrain, rostral medulla

This structure lies lateral to the oculomotor nuclei and medial to the abducens nuclei.

MLF

What nucleus is important for vertical saccadic eye movements?

riMLF

What structure is important for horizontal eye movements (conjugate gaze and saccadic)?

PPRF

What is the PPRF?

Paramedian Pontine Reticular Formation - area in pons controlling horz conjugate gaze and saccadic eye movements, referred to as Horizontal Gaze Center

Outline the cerebrospinal fluid course.

Produced in choroid plexus in lateral ventr; lateral ventr, interventr foramina, 3rd ventr, sylvian aqueduct, 4th ventr, 3 foramina, subarachnoid space, arachnoid villi in superior saggital sinus

What condition can involve extremely high intracranial pressure then go back to normal?

sleep apnea

Papilledema is an indication of what potential blockage?

cerebrospinal fluid blockage within ventricles

What are cisterns?

expanded areas within subarachnoid space of brain and spinal cord

Where is the lumbar cistern? What is its significance?

Between L2 and S2; where spinal taps are performed

___ will result in blood in the CSF.

Subarachnoid hemorrhage

___ will result in pus in the CSF.

Meningitis

ICP >200-250 mm H2O can result in...

papilledema (verify?)

T/F - CSF bathes the ON in the subarachnoid space.

True

What CNs innvervate the adnexa and eye?

CN II thru VII

What is the origin of CN II?

Ganglion cell axons from retina

CN II course?

ON ganglion cells, muscle cone, optic canal (in lesser wing of sphenoid), optic chiasm, optic tract, LGN in thalamus

Visual pathway (start @ LGN)?

LGN, optic radiations, superior retinal fibers thru parietal lobe, inf retinal fibers thru temporal lobe (Meyer's Loop), visual cortex in occipital lobe

Remember PITS:
Parietal inf VF (thus sup retina)
Temporal sup VF (thus inf retina)

Describe the pupillary fibers of CN II.

Before axons terminate in LGN, pupillary fibers exit the optic tract and enter brachium of sup colliculus, synapes in pretectal region of midbrain > intercalated neurons > EW nuclei

Iris sphincter is innervated by...

CN III

Ciliary muscle innervated by...

CN III

Name the two efferent components of the oculomotor nerve

EOMs - somatic
Pupils - efferent

Oculomotor and pupillomotor fibers make up the ___ nerve.

Oculomotor (CN III)

Where are the oculomotor nuclei found?

Midbrain at level of superior colliculus, ventral to cerebral aqueduct near midline

The oculomotor nuclei are (dorsal/ventral) to the cerebral aqueduct?

ventral

The oculomotor nuclei are (inferior/superior) and (medial/lateral) to the MLF.

superior, medial

Which cranial nerve nucleus has subnuclei?

Oculomotor nucleus

Name the muscle(s) controlled by the lateral subnuclei of CN III

IR, IO, MR

Name the muscle(s) controlled by the medial subnuclei of CN III

contralateral SR

Name the muscle(s) controlled by the central subnuclei of CN III

Bilateral LPS

The oculomotor nuclei are located at the (midbrain/pons/medulla) at the level of the ____.

midbrain, superior colliculus

Course of oculomotor fibers?

Thru red nucleus & exit @ midbrain-pontine junct; lower motor neurons join w/ fibers from EW nucleus to form CN III, thru subarach space, pass by post comm artery, enter superior aspect of cavernous sinus, thru SOF, EOMs

T/F - Pupillomotor fibers follow same course as oculomotor fibers

True

Pupillomotor fibers course?

EW nuclei > (same course as oculomotor fibers) > axons terminate at ciliary ganglion (at apex of muscle cone); post-ganglionic fibers > 6-10 short ciliary nerves running b/w choroid and sclera, end at CB and iris sphincter

What kind of palsy is described by exotropia and hypotropia with a ptosis and a possible mydriatic pupil?

CN III palsy

This CN nucleus is unique because it innervates structures contralateral to the side it's on.

CN IV

Which CN has the longest intracranial course of all the CNs?

CN IV

Which is the smallest of the CNs?

CN IV

CN IV fibers decussate and exit the _____ aspect of the brainstem at the _____ junction.

dorsal, pons-midbrain

A left trochlear nuclear lesion will cause this kind of EOM palsy.

RSO (contralateral!)

The trochlear nucleus is at the level of the ____ in the (midbrain/pons/medulla).

inferior colliculus, midbrain

CN IV exits the ____, curves around ____, passes between the ___ and ___ arteries, runs along CN ___, enters _____, goes thru ____ and innervates ____.

dorsal brainstem, cerebral peduncle, post cerebral and superior cerebellar arteries, CN III, enters cavernous sinus, thru superior orbital fissure, innervates sup oblique muscle

Trochlear nerve actions (3)?

Incyclotorsion, depression, abduction

Pt presents with diplopia worse at near and in downgaze with a head tilt to the left - you suspect palsy of which CN and what side?

right CN IV - trochlear

Remember SOTO - tilt opposite

What ventricle is next to CN VI?

fourth

Axons of CN ___ loop around the abducens nucleus.

VII

Course of CN VI: (dorsal/ventral) thru potine tegmentum, exits at ____ junction into ____ space, goes over ____ bone, into ____, thru ____, innervates ____.

ventrally, ponto-medullary junction (i.e. b/w pons and medulla), into sub-arachnoid space, over petrous temporal bone, into cavernous sinus, thru SOF, innervates LR.

Your left esotropic patient complains of horz diplopia worse at far with a head turn to the left - you suspect this CN palsy on what side?

Left CN VI (head turn same side as affected muscle)

CN V course: Exits [what side?] of the ____, goes into _____ ganglion which is located ____.

dorsal-medial side of pons, into trigeminal ganglion on the floor of the middle cranial fossa

CN V1 course?

(superior branch of trigeminal ganglion) - cavernous sinus, SOF; becomes Nasal, Frontal, Lacrimal nerves.

CN V2 course?

Trigeminal Ganglion (origin), Foramen rotundum; becomes zygomatic, infraorbital, pterygopalatine, meningeal nerves

CN V3 course?

Trigeminal Ganglion (origin), foramen ovale; becomes buccal, auriculotemporal, lingulal, inf alveolar, medial pterygoid, masseteric, and deep temporal nerves

You poke at your patient's lower lid for fun. What CN is involved here (be specific)?

CN V2 (sensory innervation of lower lid)

Remember CN V1 innervates upper lid

Ventral CN VII nucleus input?

from contralateral motor cortex

Ventral CN VII nucleus output?

ipsilateral lower facial muscles

Dorsal CN VII nucleus input?

from ipsilateral and contralateral motor cortex

Dorsal CN VII nucleus output?

ipsilateral upper facial muscles

CN VII lower motor neuron fibers: circle around ___, exit at ____ adjacent to CN ___, both CN ___ and CN ____ pass thru _____ into the _____, then thru [this skull foramen], branch to facial muscles.

abducens nuclei, exit pontomedullary jxn adj to CN VIII, both CN VII & VIII pass thru int auditory meatus into facial canal, thru stylomastoid foramen

What is the unique feature of the upper motor neuron of CN VII?

signals for voluntary movement of facial muscles comes from motor cortex of cerebrum

CN VII upper motor neuron fibers: axons travel thru ____ tract, thru ______, end up in ____, _____, and _____.

Thru corticobulbar tract, thru internal capsule, end up in ipsilateral dorsal and contralateral ventral + dorsal motor nuclei in pons.

CN VII upper motor neuron lesions result in? Why?

contralateral lower facial palsy due to bilat innervation of forehead; may have limb paralysis on same side

CN VII lower motor neuron lesions result in?

Ipsilateral upper and lower facial palsy

Your stroke patient is able to raise his forehead on both the right and left sides, but has a half smile with only the left side raised. You suspect a lesion where? Why?

Lesion at left motor cortex, resulting in loss of innervation to the right CN VII ventral facial nucleus thus a lower right facial palsy.

The left half (both upper and lower) of your patient's face is paretic. You suspect a lesion where?

Somewhere along lower motor neuron of CN VII, left side.

Cavernous sinus: anterior and medial walls? Posterior wall?

ant and medial = sphenoid, post = petrous portion of temporal

CNs in the cavernous sinus?

CN III, IV, V1, VI

T/F - Internal carotid artery is in cavernous sinus?

True

T/F - Oculosympathetic fibers in cavernous sinus?

True

What lies between the two cavernous sinuses?

Sphenoid sinus and pituitary gland

Motor fxn of CN V?

Muscles of mastication