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Chapter 14 – A
Synopsis of the
Cranial Nerves of the
Brainstem
Michelle-Lee Jones
February 18, 2009
OUTLINE
Introductory Points
 Cell Columns & Nuclei – Motor & Sensory
 Cranial Nerves of the Medulla Oblongata
 Cranial Nerves of the Pons-Medulla
Junction
 Cranial Nerves of the Pons
 Cranial Nerves of the Midbrain

Introductory Points

Regarding the brainstem:
 Transit
point for all ascending &
descending tracts connecting the spinal
cord to the forebrain
 Associated with the exit/entry & nuclei of
10/12 cranial nerves
 Lesions often involve cranial nerves & have
long tract signs  great localizing signs
Motor Cell Columns and Nuclei



Recap: basal plate derivatives  CN motor
nuclei  oriented in discontinuous
rostrocaudal cell columns
Nuclei from the same column possess
common developmental, structural and
functional features
3 motor cell columns:
 General
Somatic Efferent (GSE), General
Visceral Efferent (GVE) & Special Visceral
Efferent (SVE)
Motor Cell Columns and Nuclei
GSE column features:
1.
•
•
•
Most medial & anterior to the ventricular
space
Nuclei include hypoglossal (XII), abducens
(VI), trochlear (IV) & oculomotor (III)
Motor neurons innervate skeletal muscle
from head mesoderm – tongue (occipital) &
extraocular muscles (orbit) [ mesoderm NOT
located in pharyngeal arches]
Motor Cell Columns and Nuclei
2. GVE – preganglionic parasympathetic column
features:
•
Lateral to GSE
•
Forms cranial portion of craniosacral division of
visceromotor system (parasympathetic) &
preganglionic fibres travel on the CN
•
Nuclei include dorsal motor vagal nucleus (X),
inferior salivatory nucleus (IX), superior salivatory
nucleus (VII–intermediate), Edinger-Westphal
nucleus (III)
•
Preganglionic axons  peripheral ganglion 
postganglionic fibres  visceral structure
Motor Cell Columns and Nuclei
3. SVE:
•
•
•
Most lateral motor column in medulla &
pontine tegmentum
Nuclei include nucleus ambiguus (efferents
on IX & X), facial motor nucleus & trigeminal
motor nucleus
Muscles innervated originate from
mesenchyme located within the pharyngeal
arches
Motor Cell Columns and Nuclei
Pharyngeal
Arch
I
II
III
IV
Associated muscle
Mastication (V)
Facial expression (VII)
Stylopharyngeus (IX)
Pharynx constrictors, intrinsic
laryngeal muscles (including
vocalis), palatine muscles (except
TVP), skeletal muscle upper half
of esophagus (X)
GSE
GVE
SVE
Sensory Cell Columns & Nuclei
Recap: alar plate derivatives  CN
sensory nuclei  oriented in continuous
cell column
 Lateral location for sensory columns
 3 sensory cell columns:

 Solitary
tract and nucleus
 Vestibular/cochlear nuclei
 Trigeminal sensory nuclei
Sensory Cell Columns & Nuclei
Solitary tract & nucleus (CN VII, IX & X)
1.
•
•
•
•
Visceral afferent centre of brainstem (solitary tract
receives all the 1°visceral afferent central
processes)
Taste or Special Visceral Afferent (SVA) fibres 
Gustatory nucleus (rostral area of solitary nucleus)
General Visceral Afferent (GVA) fibres 
Cardiorespiratory nucleus (caudal area of the
solitary nucleus)
Solitary tract & nucleus (medulla) do not extend
rostrally beyond the pons-medulla junction (most
rostral CN = VII)
Sensory Cell Columns & Nuclei
Vestibular/cochlear nuclei
2.
•
•
•
•
Just posterior to solitary tract & nucleus
Includes medial & spinal vestibular nuclei,
anterior and posterior cochlear nuclei at
pons-medulla junction, superior and lateral
vestibular nuclei (caudal pons)
Sensory input from VIII only
Hearing (SSA, exteroceptive) & balance and
equilibrium (SSA, proprioceptive)
http://instruct.uwo.ca/anatomy/530/8nucl2.gif
Sensory Cell Columns & Nuclei
Trigeminal sensory nuclei
3.
•
•
From spinal cord-medulla junction to rostral
midbrain
3 subdivisions



Spinal trigeminal nucleus (pars caudalis, pars
interpolaris & pars oralis) – lateral medulla to
caudal pons
Principal sensory nucleus (mid-pontine level)
Mesencephalic nucleus (lateral to
periaqueductal grey)
Sensory Cell Columns & Nuclei
Trigeminal sensory nuclei
3.
•
•
•
Principal sensory nucleus & particularly the
spinal trigeminal nucleus  GSA reception
centre of brainstem
Receives all the general somatic afferent
(pain & thermal) central processes
CN V, VII, IX & X
Cranial Nerves of the Medulla
Oblongata (CN XII, XI, X & IX)
Hypoglossal Nerve (Motor)

Nucleus - internal to the hypoglossal trigone
 Course: anterior medulla  lateral aspects
of medial lemniscus & pyramids  preolivary fissure (rootlets)  hypoglossal
canal  intrinsic tongue muscles + hypo-,
stylo- & genioglossus muscles
 Hypoglossal Canal: XII nerve, emissary
vein, meningeal branch from ascending
pharyngeal artery (dura posterior fossa)
Hypoglossal nucleus + fibres:

supplied by anterior spinal artery (ASA)

Medial Medullary Syndrome (ASA)




Deviation of tongue to side of lesion (GG)
Contralateral hemiparesis (CST)
Contralateral loss of position sense, vibration & 2-point
discrimination (ML)
Root lesion – tongue deviation to side of lesion
Hypoglossal nucleus + fibres:

Internal capsule lesion



tongue deviation to the contralateral
side (injury to crossed corticobulbar
fibres innervating XII nucleus)
Contralateral hemiplegia
Drooping of facial muscles
contralateral lower quadrant
Accessory Nerve (Motor):

SCM and trapezius muscles are
innervated by motor neurons in the
cervical spinal cord (NOT MEDULLA)
 Cranial part of XI  misnomer (XI fibres
temporarily join vague, then separate to
exit skull)
 Course: Cervical SC  axons exit SC
laterally  merge to form nerve 
foramen magnum  briefly join caudal
part of X in post. fossa  jugular foramen
Accessory Nerve (Motor):



Root lesions: trapezius & SCM paralysis
(ipsilateral shoulder droop & difficulty
turning head to contralateral side)
C-spine lesion – above deficits are
eclipsed by hemiplegia (CST)
Internal capsule lesion – similar deficits
as above (uncrossed corticobulbar fibres
to XI nucleus injured)
Vagus Nerve (Motor & Sensory):


Intermediate location (b/w midline &
lateral medulla); exits post-olivary sulcus
(exits cranial cavity via jugular foramen)
2 ganglia immediately external to the
foramen:


Superior Ganglion (GSA)
Inferior Ganglion (GVA, SVA)
Vagus Nerve - Motor cells of
the medulla:
1. Dorsal motor nucleus of the vagus (GVE-PNS
preganglionic)  terminal (intramural) ganglia
 viscera (trachea, bronchi, heart, GI tract –
just proximal to splenic flexure
 Effects: bronchiole constriction,  HR,  blood
flow, peristalsis, gut secretions
2. Nucleus Ambiguus (SVE)  4th pharyngeal
arch muscles (refer to previous table)
Vagus Nerve – Sensory
(GSA, GVA & SVA)
1.
GSA (pain & thermal):
–
2.
Small area of ear, part of external auditory meatus & dura
posterior fossa  superior ganglion (central processes to
spinal trigeminal tract, thence to spinal trigeminal nucleus)
GVA & SVA:
–
Heart, aortic arch, pharynx & larynx, lungs, gut to level of
splenic flexure (GVA) + taste buds on epiglottis & tongue
base (SVA)  inferior ganglion (central processes to
solitary tract, thence to solitary nucleus - cardiorespiratory
& gustatory portions
GSA
SVA
SVE
GVE
GVA
Vagus Nerve – Sensory
(GSA, GVA & SVA)


Root lesion (vagus): dyphagia & dysarthria, no apparent
lasting visceromotor dysfunction, taste NA & external
auditory meatus GSA loss not key
Unilateral medulla injury  nucleus ambiguus (Tumours,
vascular lesions, syringobulbia)



Deficits as noted above
Bilateral medulla lesions  aphonia, aphagia, dyspnea,
or inspiratory stridor
 Critical, especially if dorsal motor nucleus
Thyroid surgery  recurrent laryngeal n. injury  dysarthria
Glossopharyngeal Nerve
(Motor & Sensory)

Leaves medulla @ postolivary sulcus,
just rostral to vagus, leaves skull via
jugular foramen

As with vagus, 2 ganglia: inferior
ganglion (GVA, SVA) & superior ganglion
(GSA)
Glossopharyngeal Nerve - Motor


Inferior salivatory nucleus (GVE PNS):
axons join with tympanic nerve, then
lesser petrosal nerve  otic ganglion 
parotid gland
Nucleus ambiguus (SVE): innervation of
stylopharyngeus that muscle that helps
with swallowing & efferent part of gag
reflex
Glossopharyngeal Nerve Sensory

GSA: Pinna, external auditory canal 
superior ganglion

GVA: Parotid gland, oropharynx &
carotid body  inferior ganglion

SVA: Taste from posterior 1/3  inferior
ganglion
Glossopharyngeal Nerve Lesions



Rare, usually with X & XI roots @ jugular
foramen
Nerve lesion:  taste posterior 1/3, loss of ipsi.
gag reflex (s-m X)
Glossopharyngeal neuralgia:


attacks of intense idiopathic pain in pharynx, caudal
tongue, tonsil,? middle ear
Precipitated by spontaneous or artificial stimulation
posterior oral cavity, swallowing or talking
SVA
GSA
GVE
GVA
SVE
Jugular Foramen & associated
syndromes
Right Jugular Foramen – medial, middle & caudal parts
Jugular Foramen & associated
syndromes

Vernet syndrome



@ or just internal to the foramen
Loss of sensation post 1/3 tongue (IX); loss of sensation in
larynx & pharynx, dysarthria & dysphagia (X); weakness of
ipsil. SCM & trapezius (XI)
Collet-Sicard syndrome



Immediately external to the jugular foramen
Damage to IX, X, & XI + ipsil tongue weakness (hypoglossal
canal is near foramen)
Villaret syndrome includes above + sympathetic fibres (SCG)
 ipsil Horner’s
Cranial Nerves of the Pons-Medulla
Junction (CN VIII, VII & VI)
Vestibulocochlear Nerve
(Almost exclusively sensory)



Most lateral, centrally related to cochlear &
vestibular nuclei; 2 parts originate from
specialized receptors within petrous temporal
bone  combined root in brainstem
Internal acoustic meatus (IAM) contains
VIII, VII & labyrinthine artery
Cochlear part:

Cochlear  Spiral ganglion (bipolar cells)  IAM 
Cochlear nuclei (ant. & post.)  brainstem relay
nuclei  MGN  auditory cortex
Vestibulocochlear Nerve
(Almost exclusively sensory)


Note cholinergic cells near the olivary nuclei 
olivocochlear tract (efferent cochlear bundle)
 inner & outer hair cells (dampen responses)
Vestibular part:

Ampullae of semicircular canals, utricle & saccule
 vestibular ganglion (bipolar cells)  IAM  PMJ
 vestibular nuclei (sup, inf, lat, med) in medulla &
caudal pons  cerebellum + oculomotor nuclei, etc.
Vestibulocochlear Nerve





VIII nerve lesions: hearing loss, tinnitus, vertigo,
dizziness, ataxia
Cochlea, spiral ganglion or cochlear fibres lesions:
ipsilateral sensorineural hearing loss
Lesions to brainstem or higher:  ability to
localise/interpret sound in space, no hearing loss per
se
Conductive hearing loss:  conduction through middle
ear (typically ossicles)
Tinnitus pertains to auditory portion of VIII (peripheral
or central damage)
Vestibulocochlear Nerve





Injury to vestibular fibres: vertigo (subjective – pt moves
or objective – environment moves), nystagmus ± n/v
Nystagmus – vestibular influence over brainstem
oculomotor control disconnected
Lesions of vestibular nuclei & central connections –
vertigo, ataxia, nystagmus, ± n/v
Causes of vestibular dysfunction are myriad:
 Meds, trauma, DM, cerebellar lesions, vestibular
schwannoma etc.
Meniere’s syndrome:
 hearing loss, sound distortion, vertigo, unsteadiness
standing or walking
  endolymphatic pressure   size of utricle, saccule
& cochlear
Cerebellopontine Angle Lesions
TUMOR TYPE
Vestibular schwannomas
Meningiomas
Epidermoid tumours
85%
5-10%
5%
Prevalence @
CPA
Origin/
Description

Schwann cells of
vestibular root

Margins of internal
acoustic meatus
(anterior, superior)


Clinical
manifestations


Tinnitus, unsteady gait,
progressive hearing
loss, later ipsil. facial
weakness, if > 3 cm,
impinge on V 
sensory  ± pain
Significant erosion of
internal acoustic
meatus

Early facial
weakness then
hearing loss &
trigeminal root
associated pain


Entrapped clusters
of epidermis
anywhere in CNS
Lined with
epithelium &
contain cellular
debris, proteins &
cholesterol
Spillage of cyst
contents 
recurrent aseptic
meningitis
In CPA, deficits
related to V, VII &
VIII
Facial Nerve (Motor & Sensory)
(Petrous temporal bone)
Sortie
Intermediate nerve: GVE + SVA + GSA + few GVA
Facial Nerve

At geniculate ganglion (internal genu), greater petrosal nerve
formed by GVE-preganglionic PNS nerves from VII  joins deep
petrosal nerve to form nerve of the pterygoid canal 
pterygopalatine ganglion

Post-ganglionic parasympathetic fibres join V2  orbit  lacrimal
gland

Small SVE branch  stapedius muscle

Larger SVE branch (chorda tympani)  middle ear  joins V3
lingual branch  preglanglionic PNS fibres to submandibular
ganglion, collects SVA taste afferent fibres (ant 2/3 tongue)

SVE  muscles of facial expression, post. belly digastric &
stylohyoid
Facial Nerve

Sensory:
 SVA: anterior 2/3 tongue  lingual V3 
changeover to chorda tympani to join VII
nerve  geniculate ganglion

GSA: fewer in number; external ear &
external auditory canal  central course on
VII  geniculate ganglion

GVA: few; mucous membrane of palate &
nasopharynx  geniculate ganglion  enter
brainstem in intermediate nerve
Facial Nerve

Ipsilateral face motor cortex provides
bilateral innervation to facial motor neurons
of the upper face

But, the face motor cortex projects only
contralaterally to facial motor neurons of the
lower face

Supranuclear lesions (face motor cortex or
internal capsule)  drooping of corner of
mouth contralateral to the lesion (CENTRAL
SEVEN LESION)
Facial Nerve

Peripheral lesions of VII (infranuclear):

Bell’s palsy:







Injury proximal to geniculate ganglion & origin of
greater petrosal nerve with ipsilateral findings
paralysis of upper & lower portions of face
 mucosal secretion in nasal & oral cavities
 tear fluid production & salivary gland output
 cutaneous sensation external ear & external
auditory canal
 taste sensation on anterior 2/3 tongue
hyperacusis
Facial Nerve

Peripheral lesions of VII (infranuclear):

Distal to the geniculate ganglion but
proximal to the origin of the chorda tympani
& stapedial nerve



Ipsilateral  salivation & taste, hyperacusis, 
facial expression
Intact tear fluid production & mucosal surfaces
(nasal & oral cavities) are unaffected b/c greater
petrosal nerve is intact
Caveat: Lesions distal to or @ stylomastoid
foramen  ipsil.  function of all facial muscles
in the absence of parasympathetic or taste
dysfunction
Facial Nerve

Corneal reflex:


Afferent limb travels via V1 (ophthalmic) 
trigeminal ganglion  spinal trigeminal tract 
spinal trigeminal nucleus  trigeminothalamic
fibres  facial motor nucleus  thalamus
Facial diplegia



Myotonic muscular dystrophy
Mobius syndrome (upper > lower facial
weakness typically, extraocular palsies, skeletal
& extremity defects)
Lyme disease, GBS, Botulism poisoning &
Corynebacterium diphtheriae
Mobius syndrome
Verzijl, Harriette T.F.M., van der Zwaag, Bert, Cruysberg,
Johannes R.M., Padberg, George W.
Mobius syndrome redefined: A syndrome of
rhombencephalic maldevelopment
Neurology 2003 61: 327-333
Facial Nerve

Hemifacial spasms:



Irregular painful facial muscle
contractions
May be precipitated by voluntary facial
movements or follows Bell’s palsy
Can be 2° to compression of facial
nerve root (e.g abnormal AICA
branches)
Abducens Nerve - Motor

Abducens nucleus:



Internal to the facial colliculus, in rhomboid fossa
floor just lateral to median sulcus, above stria
medullaris (IV ventricle)
Contains motor neurons (GSE) & interneurons
Abducens nerve exits @ pons-medulla
junction (pre-olivary sulcus)  cavernous sinus
in close association with ICA  superior orbital
fissure  ipsil. lateral rectus (LR)
Abducens Nerve - Motor

Interneurons in VI nucleus  contralateral
MLF  oculomotor nucleus (ipsi to MLF) 
medial rectus (MR)

Abducens fibres injury e.g. medial pontine
syndrome  flaccid paralysis of ipsilateral
lateral rectus muscle (introverted eye,
impaired ipsil. abduction)
Abducens Nerve - Motor


Abducens nucleus injury (motor- &
interneurons) e.g. IV ventricle tumour invading
facial colliculus  paralysis ipsi LR + contra.
MR on gaze toward side of lesion (LMN of LR +
INO)
Medial longitudinal fasciculus lesions 
internuclear ophthalmoplegia e.g. MS



Injury only to internuclear axons
Ipsil abduction intact ± nystagmus but adduction of
contralateral eye is impaired
Preserved adduction with convergence (vs. III )
MLF - INO
Abducens Nerve - Motor

One and a Half syndrome:


Seen with pontine lesion affecting abducens nucleus
& fibres + adjacent MLF
 No movement of ipsilateral eye horizontally,
contralateral eye horizontal movements restricted to
abduction ± nystagmus
Cortical Influence:
 Frontal eye fields (FEF)  bilateral projection to
PPRF (horizontal gaze centre) + ipsil. superior
colliculus (SC)
 SC  contralateral PPRF; PPRF  ipsil VI nucleus
 Cortical damage (e.g. CVA, trauma) to FEF 
involuntary conjugate deviation of eyes to the side
of the lesion
One-and-a-half syndrome. This results from a pontine lesion (shaded area) involving the paramedian pontine reticular
formation (lateral gaze center) and medial longitudinal fasciculus, and sometimes also the abducens (VI) nucleus, and
affecting the neuronal pathways indicated by dotted lines. Attempted gaze away from the lesion (A) activates the
uninvolved right lateral gaze center and abducens (VI) nucleus; the right lateral rectus muscle contracts and the right
eye abducts normally. Involvement of the medial longitudinal fasciculus interrupts the pathway to the left oculomotor
(III) nucleus, and the left eye fails to adduct. On attempted gaze toward the lesion (B), the left lateral gaze center
cannot be activated, and the eyes do not move. There is a complete (bilateral) gaze palsy in one direction (toward the
lesion) and one-half (unilateral) gaze palsy in the other direction (away from the lesion), accounting for the name of the
syndrome.
Clinical Neurology – 6th ed. Greenberg et. al
Cranial Nerves of the Pons
(CN V, IV, III)
Trigeminal - Motor & Sensory

Introduction:

Largest CN, exits from lateral pons

Large sensory root (portio major) & small
motor root (portio minor)

Exits border between basilar pons & middle
cerebral peduncle
V1
V2
V3
Trigeminal - Motor & Sensory

Brief review:
 Sensory nuclei (caudal  rostral):

Spinal trigeminal nucleus (pars caudalis,
interpolaris & oralis), principal sensory nucleus &
mesencephalic nucleus

GSA exteroception: Pain, thermal & nondiscriminative touch fibres from head  trigeminal
ganglion + geniculate ganglion + superior ganglia for
CN IX & X (ext. ear)  spinal trigeminal
tract/nucleus

GSA exteroception for discriminative touch  as
above but go to principal sensory nucleus
Trigeminal - Motor & Sensory

GSA proprioceptive input from
masticatory muscles, EOM & periodontal
ligament receptors  mesencephalic
nucleus

Sensory input to spinal trigeminal nucleus
& to principal sensory nucleus  anterior
& posterior trigeminothalamic tracts 
thalamus  somatosensory cortex
Trigeminal - Motor & Sensory



Motor nucleus of V  1st pharyngeal arch
(medial & lateral pterygoid, tensor
tympani, tensor veli palatini, mylohyoid, &
anterior belly digastric)
The motor root of V exits in the foramen
ovale along with V3.
Jaw Jerk reflex:

Masticatory muscle receptors  V2 
mesencephalic nucleus  bilateral
projections from afferent collaterals 
trigeminal motor nucleus
Trigeminal - Motor & Sensory


Corneal (previously discussed)
Lesions of V nerve or central nuclei

Sensory sx in nerve distribution &
masticatory muscle paralysis
 Sensory deficits include:



Complete loss of pain, temperature, tactile
sensation ipsilateral face & scalp
Loss of above sensations in oral cavity ipsil.
Loss of corneal reflex
Trigeminal - Motor & Sensory

Tic douloureux (Trigeminal neuralgia)








Severe paroxysmal attacks of lacinating pain
restricted to ≥ 1 subdvisions of V
Trigger zones – lip, nose, cheek
Precipitants e.g. shaving, make-up application,
chewing, talking etc.
Possible malnourishment!!!
Patients usually > 35 years
Maxillary > Mandibular > Ophthalmic
Associated with MS, degenerative changes in
trigeminal ganglion, vascular abn (e.g. SCA) –
contradicting autopsy evidence
Status trigeminus  tic like contractions masticatory
muscles
Trigeminal - Motor & Sensory

Motor deficits:

V root lesion  ipsil masticatory muscle
weakness, jaw deviation to weak side
(unopposed contralateral pterygoid)

Central lesions (tumour, AVM, mets,
vascular obstruction)

Lateral Medullary syndrome (Wallenberg
syndrome)
Cranial Nerves of the Midbrain
(CN IV, III)
Trochlear – Motor

Only motor CN to cross midline prior to
exit & has long intracranial course

Course: Trochlear nucleus (post. to MLF)
@ level of IC  arch around PAG 
decussates in anterior medullary velum
 exits brainstem immediately caudal to
the contra. IC  GSE motor axons 
superior cistern  ambient cistern 
dura  cavernous sinus  superior
orbital fissure  superior oblique (inf-lat)
Trochlear – Motor


Trochlear motor neurons innervate
contralateral superior oblique
MLF + trochlear nucleus lesion e.g. MS:



Contralateral S.O. paralysis
Ipsil INO
Cotical input:




FEF  rostral interstitial nucleus of the MLF &
superior colliculus
riMLF = vertical gaze centre
riMLF  larger projection to ipsil IV nucleus &
smaller projection to contra nucleus
FEF injury involuntary conjugate gaze
deviation to side of lesion
Oculomotor – Motor

Situated within ventral PAG, posterior to MLF,
in rostral half of midbrain

GSE  all EOM except SO & LR

Ipsilateral innervation except for SR neurons
(decussate within the nucleus)

Just posterior to III complex is EdingerWestphal nucleus (GVE – PNS)  ciliary
ganglion
Oculomotor – Motor

Course:



III nerve fibres travel ventrally through & around the
red nucleus  exit @ interpeduncular fossa 
cavernous sinus  superior orbital fissure
Superior & inferior divisions of III in the orbit 
few branches to ciliary ganglion
Ciliary ganglion (PNS)

 short ciliary nerves  sphincter pupillae & ciliary
muscles
Oculomotor – Motor
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Post ganglionic sympathetic fibres from SCG
travel on ICA plexus  ophthalmic artery 
optic canal  ciliary ganglion directly,
nasociliary branch (V2) or oculomotor on route
to ciliary ganglion
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In ciliary ganglion: SNS fibres continue directly
into short ciliary nerves to dilator pupillae
muscle, and others travel further via III nerve
 superior tarsal muscle
Oculomotor – Motor
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Sensory input from the orbit via frontal &
nasociliary nerves  V1  trigeminal ganglion
The III nucleus does not receive direct
cortical input via the corticobulbar system
Cortical control of III neurons via riMLF and
SC; SC also projects to the riMLF; riMLF send
significant input to ipsi III, less on contralateral
side
Cortical damage to FEF  involuntary
conjugate deviation towards the side of lesion
Oculomotor – Motor

Lesions of III nucleus, oculomotor nerve in
interpeduncular cistern or III in cavernous sinus:
 EOM paralysis except for SO & LR ( abducted &
depressed)
 Diplopia
 Pupil dilation, non-reactive to light, defective
accommodation & ptosis
 Note that because of peripheral location of PNS
fibres, subtle initial signs with external compression
may be ptosis or mildly diminished pupil reactivity
prior to EOM dysfunction
 DM: EOM dysfunction sine visceromotor changes
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Ischemia affects the larger internal GSE motor axons 1st