L9: Pons extended version

hering’s law of equal innervation

yoked muscles have equal innervation - 2 eyes

ex:

left lateral rectus stimulated

right medial rectus is stimulated equally

sheringtons law of reciprocal innervation

antagonist muscles in the same eye recieve equal and opposite innervation

position of eyes at rest and why

straight ahead

bc they have tone due to intact innervation

nucleus propositus hypoglossi

neural integrator for horizontal movements

helps keep eyes still along horizontal

medulla

what has to work for normal lateral gaze

1. muscles

   1. ipsilateral LR

   2. contralateral MR

2. Nerves

   1. CN 6 - LR

   2. CN 4 - MR

3. Nuclei

4. Brainstem

   1. MLF - interconnects nuclei of 6 and 3

   2. PPRF

5. cerebral cortex

   1. frontal eye fields

   2. corticobulbars

lesion of L CN 6

left eye doesnt turn out - eso

6 nerve palsy

if you damage CN 6 nucleus do you get an abduction deficit

no

lateral gaze center = gaze palsy

damage to what causes an abduction deficit

abducens nerve

what things other than a CN 6 palsy could cause an abduction deficit

1. damage to lateral rectus

2. damage to NMJ (myasthenia gravis)

3. etc

what does raymonds syndrome affect

6 and contralateral hemplegia

• gets CN 6 - ipsilateral abduction

• also corticospinals - above crossing

what is this green box a lesion of

raymonds syndrome

what does aqua oval cause

millard gubler syndrome

millsard gubler syndrome

1. 6 - ipsalateral abduction

2. 7- ipsilateral, LMN

3. contralateral hemiplegia

lesions dorsally (tegmentum) can get ________

CN

- likely to get sensory pathways

lesions ventrally can get

• CN

• mote likely to get vol motor pathways

LMN of 7 affects (top/bottom) face

all

what does this lesion cause

1. numbness is bc of red sensory fibers

2. weakness is from corticobulbars

3. its upside down

what is prepontine cistern a part of

subarachnoid space

• could get a meningioma

what is in the subarachnoid space that could damage CN 6

1. blood vessels

2. Anterior inferior cerebellar arery

3. labrynthine artery

4. (blood vessels)

all CN transverse the ___________

subarachnoid space

name the arteries that travel near CN 6

1. Anterior inferior cerebellar arery

2. labrynthine artery

where are the arteries that come near CN 6

cerebellar pontine artery

what CN could be involved in a cerebellopontine angle mass - specifically a vestibular Schwannoma

6, 7, 8

what bone is the clivus made of

occipital

both the right and left CN 6 travel up ______

clivus

what does an issue w the MLF cause

adduction

what can damage CN 6 when traveling up the clivus

spread of nasopharyngeal carcinoma

what other than CN 6 can be damaged by the spread of nasopharyngeal carcinoma

pterygopalatine ganglion - decreased tearing

whats the synapse of GSPN (CN 7)

pterygopalatine ganglion

prior to entering dorellos canal, CN 6 travels close to

inferior petrosal dural venous sinus

ligament —— pushes down and pinches 6 against bone

CN 6

petrous portion of temporal bone

what ligament pushes on CN 6 and pushes it into petrous portion of temporal bone

petroclinoid ligament (of Gruber)

• under that is dorellos canal

which CN can be compressed by increased ICP as it is traveling in Dorellos canal

6

papilledema

bilateral in distinct margins that can be caused by ICP that can cause the ligament to push onto CN 6 and shove it into the petrous portion of temporal bone

any time there is an abductino deficit there could be

optic disc edema

potential causes of papilledema/ increaed ICP

1. epidural hematoma

2. subdural hematoma

3. meningitis

4. intracranial mass

5. dural venous sinus thrombosis

6. idiopathic intracranial hypertension

gradenigo syndrome

• can affect CN 6

• (and 5)

• associated w bacterial otitis media w petrous apex involvement

• spread of infection from middle ear or mastoid

• spreads intracranially via roof

whats the ear discharge in gradenigo syndrome

1. CSF flows into middle ear

what causes pain in gradenigo syndrome

CN V

facial/scalp/periorbital

what does gradenigo do to the eyes

1. diplopia from CN 6 palsy abduction deficit

whats the pathway of CN 6

1. low pons

2. subarachnoid space

3. prepontine cistern

4. clivus

5. dorellos canal

6. cav sinus

7. SOF

8. orbit

9. lateral rectus

a lesion affecting CN 3 and 6 is probably a lesion of

cav sinus

what can affect CN 6 in cav sinus

1. meninges

   1. meningioma

      1. Horners and ipsilateral 6 nerve palsy

         1. 6 and ICA (SYMPATHETICS) travel together in caudal cav sinus

2. ICA anneurysm

   1. 6 travels in the caudal cav sinus adjacent to ICA

would you rather have a PCOM or ICA in cav sinus anneurysm

PCOM

would you rather have a RUPTURED anneurysm of PCOM or ICA

PCOM = subaachnoid hemmorhage = death

ICA = cav sinus = in an enclosed venous sinus

is this a ptosis or mueller issue

1. ptosis - its large

what can we get in the cav sinus due to the fact htat it is a dural venous sinus

venous thrombosis

• this creates resistance to flow so blood will stay backed up in the eye

carotid cavernous fistula - opening of ICA

• high flow arterial blood in the Cav sinus makes it difficult for venous blood to get out of the eye and into the cav sinus

does CN 6 travel in or out of the tendinous annulus

inside

Duane’s Retraction syndrome

1. CN 6 and/or its nucleus fails to develop

2. so, 3 helps it out and

   1. usually only goes to medial rectus but also goes to lateral rectus

3. this will cause a crazy thing with sheringtons law —> so the eye sinks back in the globe

whatas the most common Duanes retraction syndrome

Type 1 - abduction deficit w normal adduction

• abduction deficit

• and the eye goes back in globe == thats bc when you use 3 to adduct its also connected to 6

gaze palsy

1. lesion of CN 6

primary gaze lesion of left CN 6

1. no tone from lateral rectus = ESO left eye

right gaze w a lesion of L CN6

1. look towards R and we can

   1. could have R gaze preference - if we try to look straight ahead we have our eyes to rest

   2. eyes point contralateral to lesion

left gaze w a lesion of L CN6

neither eye can look

foville syndrome

1. cause of a gaze palsy affecting the abducens nuc and CN 7 in pons

2. can also affect the autonomic fibers so we could get a Horners Syndrome

what type of weakness do we get contralateral to the gaze palsy w foville syndrome

contralateral

lesion of frontal eye fields

1. another cause of gaze palsy but it is not related to the abducens nuc in the pons

2. related to damage to the cortex

when we stimulate the frontal eye feilds the eyes will move to the _______ sid e

contralateral

where are the FEF

precentral gyrus (closer to motor bc this is motor)

in FEF lesion, the weakness is _______ to the gaze palsy

ipsilateral

In CN 6 nuc lesion, the weakness is _______ tot he gaze palsy

contralateral

distinguish cortical lesion (FEF) form pontine lesion (CN 6 nuc)

1. FEF = ipsilateral weakness to gaze palsy

2. CN 6 nuc = contralateral weakness to gaze palsy

abducens nucleus is for

ipsilateral lateral gaze

FEF are for

contralateral lateral gaze

a gaze palsy and an UMN CN 7 palsy localizes to

FEF/Cortex

a gaze palsy and a LMN palzy localizes to

low pons

internuclear opthalmoplegia (INO)

1. lesion of MLF

2. paralysis of ipsilateral (to lesioned MLF) eye adduction

3. good eye shakes

4. caues an adduction deficit

5. ex: lesion of right MLF - person can abduct but not adduct

two most common causes of internuclear opthalmoplegia

1. demyelination - multiple sclerosis —> YOUNG PERSON

2. vasculopathic - stroke, infarction —> OLD PERSON

INO - w MLF lesion if it is in pons convergence is ________

spared

INO - w MLF lesion in midbrain - convergence is _________

abolished