PT 712 - Week 1

CN I name

olfactory

CN I - olfactory - primary function

smell

CN II name

optic

CN II - optic - primary function

vision

CN III name

oculomotor

CN III - oculomotor - primary fuction

- upward

- medial

- downward

- up and in

CN IV name

trochlear

CN IV - trochlear - primary function

down and in

CN V name

trigeminal

CN V - trigeminal - primary function

touch - forehead and cheek

- clench teeth

CN VI name

Abducens

CN VI - Abducens - primary function

- abduction

CN VII name

facial

CN VII - facial - primary function

- taste for anterior 2/3 of tongue

- smile

CN VIII name

vestibulococlear (acoustic)

CN VIII - vestibulocochlear - primary function

- hearing

- equilibrium

CN IX name

glossopharyngeal

CN IX - glossopharyngeal - primary function

- posterior 1/3 of the tongue

- speech

CN X name

vagus

CN X - vagus nerve - primary function

- digestion

- defecation

- slowed HR

CN XI name

spinal accessory

CN XI - spinal accessory - primary function

shoulder shrug

CN XII name

hypoglossal

CN XII - hypoglossal - primary function

- tongue movement

CN III (oculomotor nerve) innervates which eye muscles?

- medial rectus

- superior/inferior recti

- inferior oblique

CN IV (trochlear nerve) innervates which eye muscle?

superior oblique

CN VI (abducens) innervates which eye muscle?

lateral rectus

action of the superior rectus

turns eye upward and inward

action of the superior oblique

turns eye downward and outward

action of the medial rectus

turns eye inward

action of the lateral rectus

turns eye outward

action of the inferior rectus

turns eye downward and inward

action of the inferior oblique

tuns eye upward and outward

define visual acuity

clarity of vision and is dependent on optical and neural factors

what optical and neural factors does visual acuity depend on?

- sharpness of the retinal focus within the eye

- health and functioning of the retina

- sensitivity and interpretative faculty of the brain

Which cranial nerve function is visual perception?

CN II (optic nerve)

Which cranial nerves are for oculomotor control?

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

the image must be held steady on the _______ of the retina for a clear picture

fovea

if the image is not held steadily on the fovea of the retina, what can occur?

- blurry vision

- diplopia (double vision)

- eye strain

- dizziness

- oscillopsia (world moves with head movements)

- disequilibrium (balance and vision linked)

describe the pupillary light reflex

light shined into 1 eye constricts both pupils

When describing the pupillary light reflex, the optic nerve projects onto the lateral geniculate nucleus and also travels down a parallel path to the _______________

oculomotor nuclei

When stimulated by the optic nerve, the oculomotor nuclei sends (bilateral/unilateral) projections down the oculomotor nerve and causes (ones or both) eyes to constrict

bilateral

both eyes

in the pupillary light reflex, which cranial nerve is afferent and which is efferent?

Afferent: CN II (optic nerve)

Efferent: CN III (oculomotor nerve)

What other parasympathetic function does CN III (ocolomotor) have?

provides accommodation for near vision

decreases tension on ligaments that hold the lens to flatten it to allow focus

name some functional implications of oculomotor control

- visual proprioception

- fix eyes on and maintain stable visual targets

- potential collision anticipation

- anticipating motor control/postural control requirements

define nystagmus

- involuntary rhythmic conjugate eye movement

- may be spontaneous, gaze evoked or positional

how is nystagmus named?

named by the direction of the fast phase

What is the peripheral nervous system source of nystagmus

- damage to vestibular receptor or nerve

- engaged when head rotation exceeds limits of eye rotation, to produce a slow phase eye movement (VOR) in one direction and a fast saccadic "reset" back towards primary position

what is the central nervous system source of nystagmus?

occurs as a result of number of different brain conditions or damage to certain brain (stem) structures

What are 3 examples of physiological (normal) nystagmus?

- end point

- rotary

- optokinetic nystagmus

describe end point nystagmus

nystagmus is observed at end-point in 30% of healthy individuals

describe rotary nystagmus

occurs when head spinning is induced

describe optokinetic nystagmus

keeping moving targets on fovea

What are 3 types of pathological nystagmus?

- spontaneous

- gaze-evoked

- positional

describe gaze evoked nystagmus

- damage to neural integrator

- must be differentiated from end-range nystagmus

What are the 6 neuronal control systems for vision?

- visual fixation

- VOR (vestibular ocular reflex)

- OKR (optokinetic reflex)

- pursuit

- saccades

- vergence

define visual fixation

maintains visual gaze on a singular location

define pursuit

hold images of a moving target stable on the retina

define extraocular movement

muscle testing of the eyes

define ocular alignment

maintains eyes centered in the socket

define saccades

rapid movements of the eyes to place the object of interest on the fovea

define vergence

adjusts the eyes for different viewing distances

define vestibular ocular reflex

stabilizes images on fovea of retina during head movement

define optokinetic reflex

hold images of moving targets on the retina

What are the 6 tasks included in the oculomotor exam?

- alignment

- spontaneous and/or gaze evoked nystagmus

- extra ocular movements

- smooth pursuit

- saccades

- convergence

describe the ocular misalignment: exotropia

one or both eyes turn outward

describe the ocular misalignment: hypotropia

one eye deviates downward relative to the other

describe the ocular misalignment: esotropia

one or both eyes turn inward

describe the ocular misalignment: hypertropia

one eye deviates upward compared to the other

how to test Gaze-evoked nystagmus (GEN) in the clinic?

- move object 30 degrees to side of midline and have patient maintain position

- test both horizontally and vertically

- test with and without fixation

- note presence and direction of nystagmus

How to assess extra-ocular movements in the clinic

- determine if ROM is full and gaze is conjugate (eyes move together)

what does abnormality of extra ocular movements indicate?

potential cranial nerve abnormality

How to test smooth pursuit in clinic?

- smoothly move discrete target 30 degrees from center horizontally and vertically

what is abnormal finding in smooth pursuit?

- abnormal if catch up saccades are seen

- abnormality may indicate CNS involvement

Where are saccadic pulse generators located?

brainstem and cerebellar sites

what are the brainstem and cerebellar sites the saccadic pulse generators are located in?

- paramedian pontine reticular formation

- nucleus of the dorsal raphe

- rostral interstitial nucleus of MLF

- pontine nuclei

- medial vestibular nucleus (medulla)

- vestibulo-cerebellum

What are the cortical and higher level control areas that project onto saccade generators?

- superior colliculus

- frontal eye field

- posterior parietal cortex

- basal ganglia

how to test saccades in the clinic?

- hold object 15-20 degrees from midline

- ask pt to shift gaze from nose to object and back (left, right, up, down)

what are normal and abnormal responses to saccade testing?

normal: 2 movements to get to the target

abnormal

- eyes undershoot more than 10% of the distance or overshoot at all

- hypermetria always indicates CNS involvement

What is vergence?

moves the eyes in opposite directions to keep images at different distances stable on the fovea

what is the vergence triad?

- convergence

- acommodation

- mitosis

convergence

move inward

divergence

move outward

where are the neurons that control vergence located?

distributed in teh rostral superior colliculus of the MIDBRAIN in the same regions as control centers for saccades and pursuit

near the point of convergence

target DOUBLES

6-10 cm

near the point of accommodation

target BLURS

15 cm

Where does CN III (oculomotor) originate?

midbrain

(visible from ventral view)

Where does CN VI (abducens) originate?

pons

(visible from ventral view)

where does CN IV (trochlear) originate?

midbrain

(visible from dorsal view)

describe the pathway for horizontal conjugate gaze mechanism

- information arises to abducens nucleus

- CN IV activates ipsilateral lateral rectus

- information also crosses to contralateral MLF to oculomotor nucleus

- this activates CN III to activate contralateral medial rectus

Why is it difficult to localize source of impairment with deficits in horizontal conjugate gaze mechanism?

can't clearly differentiate between midbrain and pons

If a patient is having deficits with vertical conjugate movements where is the lesion?

midbrain

(not vestibular)

oculomotor neurons are recruited (bilaterally/unilaterally?) for vertical eye movements?

bilaterally

a lesion of Abducens Nucleus will result in a loss of....

- ipsilateral lateral rectus

- contralateral medial rectus d/t effect on contralateral MLF

A lesion of the Abducens nucleus will result in what gaze deficit?

no ipsilateral horizontal gaze (toward side of lesion)

A lesion of Abducens Nucleus will result in what primary gaze deficit?

IPSILATERAL esotropia

Only the ipsilateral eye to the lesion will be affected with esotropia, why?

- contralateral eye has only lost ability for conjugate gaze because its not getting input from MLF

- medial rectus holds in primary gaze

A lesion of the MLF (PONS OR MIDBRAIN) will cause what oculomotor deficits?

ipsilateral eye cannot ADDuct d/t lack of input to ipsilateral medial rectus

what would a lesion of L MLF look like in clinical exam?

what is the primary gaze deviation associated with lesion of MLF (pons or midbrain) internuclear ophthalmoplegia (INO)

there is no primary gaze deviation