7. CN II, III, IV and VI Flashcards by J L

CN II - Optic N.
____ mediate vision from the photoreceptors (rods and cones) of the retina

Rods and cones transduce light energy into an electrical signal which passes to ____ cells (the primary sensory neurons in the visual pathway), then ____ cells

The axons of retinal ganglion cells from the ____

special somatic afferents (SSA)
bipolar
ganglion
optic nerve

How well did you know this?

Not at all

Perfectly

MIDDLE CRANIAL FOSSA

Optic Canal
Chiasmatic Groove

After coursing through the OPTIC CANALS, the optic nerves end grossly at the level of the ____ where a decussation of fibers occurs

optic chiasm

How well did you know this?

Not at all

Perfectly

Decussating fibers are vulnerable here to lesions of the ____ and the ____ diencephalon
including the ____

pituitary gland
ventral
hypothalamus

How well did you know this?

Not at all

Perfectly

The OPTIC NERVE is technically NOT a nerve, but a ____ of the CNS, because…

Like CN I, it is comprised of axons of ____, rather than primary, sensory neurons
It is covered with CNS ____ and ensheathed by the ____

white matter tract
secondary
myelin
meninges

How well did you know this?

Not at all

Perfectly

Ganglion cell axons converge toward the ____, where they turn posteriorly, pass through the ____ of the sclera and exit the eyeball

The ____ features the densest concentration of cones and a ____
ratio of cones to ganglion cells for maximal visual acuity and color vision

optic disc
lamina cribrosa
macula
1:1

How well did you know this?

Not at all

Perfectly

Consistent with the idea that the OPTIC NERVE is a CNS tract, note that upon leaving the LAMINA CRIBROSA, the nerve is bathed in ____ and invested with all ____ meningeal layers

Increased pressure in the subarachnoid space may compress CN II and produce swelling of the nerve: ____

Recall the Central artery of the retina?

CSF
three
papilledema

How well did you know this?

Not at all

Perfectly

Ophthalmoscopic examination of the ____ is a crucial part of any clinical neurologic evaluation

May provide clues as to the presence of ____ leading to an increase intracranial pressure (ICP)

optic fundus

intracranial disease

How well did you know this?

Not at all

Perfectly

GANGLION CELLS receive Inputs primarily from
the ____ CELLS

BIPOLAR CELLS are the primary ____ neurons in the visual pathway, receiving inputs from the specialized retinal photoreceptor cells……the
____ and ____

… but ca. 10% project to brainstem (midbrain) nuclei or hypothalamus to provide visual inputs crucial for:
	• Reflex maintenance of \_\_\_\_
	• Coordination of \_\_\_\_
	• Control of the size of the \_\_\_\_
	• \_\_\_\_ regulation

bipolar
sensory
rods
cones

balance
eye movements
pupils
pineal gland

How well did you know this?

Not at all

Perfectly

Axons from the NASAL HALVES of the retinas, receiving inputs from the ____
VISUAL FIELDS, cross the midline at the
____

Most axons in each
OPTIC TRACT
terminate in the
____ of the THALAMUS…

temporal
optic chiasm
lateral geniculate nucleus

How well did you know this?

Not at all

Perfectly

Visual inputs project to PRIMARY VISUAL CORTEX surrounding the ____ fissure in the ____ LOBES of the brain

calcarine

occipital

How well did you know this?

Not at all

Perfectly

Within the optic chiasm, axons from the nasal halves of the retinas cross the midline… … resulting in the information from the
____ half of the visual
field from both eyes being
carried in the ____ optic tract and vice versa

right

left

How well did you know this?

Not at all

Perfectly

CN II Lesions

Prechiasmatic - to ____ or ____
- ____
- glaucoma (atrophy of optic disc w/ inc IOP)
- ____ (MS, syphillis, lyme)
- facial trauma
Chiasmatic - to ____
- ____ (benign neoplasias)
- ICA aneurysm
Postchiasmatic - lesions to ____, LGN or ____
- ____, TBI, neoplasm

retina
optic nerve
macular degeneration
optic neuritis

optic chiasm
pituitary adenomas

optic tract
optic radiations
stroke

How well did you know this?

Not at all

Perfectly

Prechiasmatic lesion - ____
Chiasmatic lesion to ducssating axons from ____

If the lesion to the nerve is incomplete, a ___ or blind spot in that eye’s visual field results

mononuclear blindness
nasal hemiretinae
scotoma

How well did you know this?

Not at all

Perfectly

Prechiasmatic lesion - mononuclear blindness

If the lesion to the nerve is incomplete, a
____
or blind spot in that eye’s visual field results

Chiasmatic lesion - to decussating axons from nasal hemiretinae
Temporal visual fields are lost: loss of
peripheral vision ____

____ lesion

scotoma
“tunnel vision”
postchiasmatic

How well did you know this?

Not at all

Perfectly

Having completed study of both CN II and CN V1 we must now examine the other cranial nerves
found within each orbital cavity……all of which enter the orbit through the ____

superior orbital fissure

How well did you know this?

Not at all

Perfectly

CN III Oculomotor Nerve

CN III arises from the medial aspect of the CEREBRAL ____ of the midbrain

GSE
fibers
innervate most ____ muscles

GVE
fibers
are ____ synapsing in the ____ ganglion

peduncles
extraocular
preganglionic parasympathetic
ciliary

How well did you know this?

Not at all

Perfectly

CN IV Trochlear Nerve

CN IV exits the brain below the ____ on the ____ aspect of
the MIDBRAIN

GSE
fibers
innervate the ____

inferior colliculus
dorsal
superior oblique

How well did you know this?

Not at all

Perfectly

CN IV follows the ____ intracranial course of any of the cranial nerves

Note that, atypically, the LMNs lie ____ to the SO muscle innervated

longest

contralateral

How well did you know this?

Not at all

Perfectly

CN VI Abducent Nerve

CN VI leaves the brain from the ____ SULCUS

GSE fibers innervate the ____ muscle

Note that
the LMNs lie ____ to the LR muscle innervated

inferior pontine
lateral rectus
ipsilateral

How well did you know this?

Not at all

Perfectly

CN VI follows the longest ____ course of any cranial nerve… Thus it is frequently involved in ____!

intradural

intercranial disease

How well did you know this?

Not at all

Perfectly

Before we can discuss
what happens in the CILIARY GANGLION we must look at CN V1 as well because… …As a rule, ____ axons arising from the parasympathetic ganglia in the head reach their targets by “piggy-backing” on branches of CN ____

postganglionic

How well did you know this?

Not at all

Perfectly

V1 HAS THREE MAIN BRANCHES IN THE ORBIT

____ nerve
Frontal nerve
____ nerve

nasociliary

lacrimal

How well did you know this?

Not at all

Perfectly

A quick review of the extraocular muscles is needed to appreciate the distribution
of the ____ fibers in the oculomotor nerve

GSE

How well did you know this?

Not at all

Perfectly

The MEDIAL and LATERAL RECTUS muscles move the eyeball around a single ____ axis only

Lateral rectus - ____
Medial rectus - ____

vertical
abduction
adduction

Each of the remaining muscles moves the eye around all ____ of these rotational axes This is explicable by considering the disparity of the ____ and ____ AXES

three visual (optical) orbital

Inferior oblique ____ ____ ____ Superior oblique ____ ____ ____ Superior rectus ____ ____ ____ Inferior rectus ____ ____ ____ Recall that ____ and ____ occur around a transverse axis through the center of the eyeball

elevates abducts extorts depresses abducts intorts ``` elevates adducts intorts depresses adduts extorts ``` elevation depression

Recall too that ____ and ____ occur around a Vertical axis through the center of the eyeball

abduction | adduction

Testing extraocular muscles is important for diagnosing lesions of cranial nerves ____, ____ and ____, ____ and ____ Since some of the muscles share common actions (e.g. elevation and depression), it is essential to i____ and test each muscle separately

``` III IV VI midbrain pons ``` isolate

Isolating individual muscles which share elevation or depression functions is accomplished by first either abducting or adducting the eye so as to place the selected muscle at the maximal mechanial advantage, ____ to the transverse axis through the eyeball, and the synergist at a disadvantage, ____ to that same transverse axis

perpendicular | parallel

FOR EXAMPLE, with adduction, SUPERIOR RECTUS lies almost parallel to the ____ Axis around which elevation and depression occur the SR Thus it has no ____ advantage and is unable to elevate the eyeball Only the ____, perpendicular to the transverse axis, may elevate the adducted eyeball

transverse mechanical inferior oblique

In abduction, INFERIOR OBLIQUE lies almost parallel to the ____ axis and is thus unable to elevate the eyeball Thus only the ____, perpendicular to the transverse axis, may elevate the abducted eyeball

transverse | superior rectus

TO TEST THE MUSCLES INNERVATED BY CN III - ____ NERVE

oculomotor

To test CN IV: ____ | To test CN VI: ____

superior oblique | lateral rectus

Before passing through the superior orbital fissure, CN III, IV and VI all course through the ____

cavernous sinus

``` All ____ nerves are vulnerable to compression and lesion within the CAVERNOUS SINUS resulting from: - ____ of the cavernous sinus Intracavernous ____ aneurysms 3) Aneurysms of components and branches of the ____ 4) ____ expanding ____ tumors ```

``` three septic thrombosis ICA circle of willis laterally pituitary ```

Lesions of CN III, IV or VI produce ____- paralysis of extraocular musculature

ophthalmoplegia

Right oculomotor nerve lesion(GSE) * Ptosis (drooping) of eyelid from paralyzed ____ * Eyeball “down and out”(abducted and slightly depressed) because ____(6) and ____(4) are unopposed... * So all muscles paralyzed except ____ and ____

``` levator palpebrae superioris LR SO LR SO ```

This woman demonstrates a lesion of the left CN ____ Left eyeball is ____ due to the unopposed pull of the ipsilateral ____ rectus

VI adducted medial

Paralysis of the lateral rectus is one cause of ____, the inability to direct both eyes towards the same object, which produces ____ On attempted left lateral gaze On normal right lateral gaze ____ (From a CNVI lesion produces ____ diplopia)

``` strabismus diplopia (double vision) ``` medial strabismus horizontal

RIGHT TROCHLEAR NERVE (CN IV) PALSY With the loss of the ____, which depresses and abducts, the eyeball is ____ and ____ Patient will complain of a ____ diplopia when he attempts to depress the affected eye This is particularly alarming when descending ____!!! Patient may tilt his head ____ from the side of the lesioned CN IV to reduce the diplopia

superior oblique elevated adducted vertical stairs away

In order to either maintain or change visual fixation on a moving object, the eyes must move together with exquisite precision as the result of coordinated contraction of the ____ muscles in each orbit This requires ____ co-ordination and control above the ____ of the cranial nerves

extraocular CNS brainstem nuclei

FRONTAL EYE FIELDS The ____ contains centers for conjugate eye movements \

frontal lobe

Cortical centers initiating ____ eye movements which redirect gaze are found In the the ____ eye fields They override involuntary brainstem centers in the ____ and ____ which normally coordinate the conjugate ____ of gaze on moving objects by both eyes

``` voluntary frontal pontine reticular formation midbrain fixation ```

It is now time to consider the AUTONOMIC INNERVATION of orbital structures The shape of the LENS is adjusted by contraction of the ____ MUSCLE to keep the image of an object moved nearer to the eyes in sharp focus - Ciliary muscle - Zonule fibers

ciliary

Contraction of the ciliary muscle ____ the curvature of the lens and enables ____... an adaptation of the visual apparatus for ____ viewing Near vision also requires ____ of the pupil... and ____ of the eyes resulting from bilateral contraction of ____ RECTUS

increases accommodation near constriction convergence medial

The ____ is under the active control of two antagonistic muscles: a ____ and a ____ The ____ is the central aperture of the IRIS, which functions like the diaphragm of a camera

diameter constrictor dilator pupil

The PUPILARY CONSTRICTOR and CILIARY MUSCLES are innervated by ____ arising from ____ GANGLION

postganglionic parasympathetic | ciliary

Light directed into either eye usually produces ____ pupillary constriction

bilateral

____ - inequality in the size of the pupils under changing light conditions - suggests a lesion in a pupillary ____ pathway

anisocoria | autonomic

____ fibers in CN III are carried in the ____ division of the nerve and synapse in the CILIARY GANGLION Postganglionic fibers are carried by branches of the ____ nerve to their targets

GVE inferior nasociliary

CNIII PATHWAY!

IN SUMMARY, POSTGANGLIONIC PARASYMPATHETICS FROM THE CILIARY GANGLION DISTRIBUTE TO: PUPILLARY ____ If this parasympathetic pathway is lesioned... • The pupil will be fixed and ____ • The PUPILARY ____ (CN ____-CN____) will be lost ____ MUSCLE If this parasympathetic pathway is lesioned...____ vision will be impaired

``` constrictor dilated (mydriasis) light reflex II III ``` ciliary near

Right oculomotor nerve lesion * NO pupillary ____ reflex (constriction of pupil in affected eye in response to light) * Dilation of ____, since parasympathetics are interrupted and ____ is unopposed * No accommodation of lens because ciliary muscle is paralyzed - LOSS OF ____ VISION

light iris dilator pupillae near

Considering the SYMPATHETIC innervation of orbital structures opens us up to recalling the origin of all head and neck sympathetics ____. and the ____ of the upper eyelid

pupillary dilator muscle | superior tarsal muscle

``` Almost all postganglionic sympathetic fibers supplying the head are distributed through the ____ PLEXUSES which surround the INTERNAL and EXTERNAL ____ ARTERIES and their branches ``` THE POSTGANGLIONIC SYMPATHETIC INNERVATION OF THE HEAD ARISES FROM THE ____

periarterial carotid superior cervical ganglion

Preganglionic sympathetic innervation of the orbit arises from the ____ CORD SEGMENTS These fibers ascend thru the cervical sympathetic chain and synapse in the ____ The postganglionic fibers run in the ____ NERVE and PLEXUS and then enter the orbit... ...They run through the ciliary ganglion without ____ and travel on ____ NERVES (____ and ____) to reach their targets ``` THE SYMPATHETICS IN THE ORBIT INNERVATE: • The ____ • The ____ • The ____ and its branches ```

``` T1-T2 superior cervical ganglion internal carotid synapsing ciliary long short ``` pupillary dilator superior tarsal muscle ophthalmic artery

Recall that branches of the OPHTHALMIC ARTERY distribute to the forehead, root and bridge of the nose - ____ - ____ - ____

supraorbital supratrochlear dorsal nasal

Horner's Syndrome INTERRUPTING THE SYMPATHETIC PATHWAY DESCRIBED PREVIOUSLY PRODUCES THE FOLLOWING SYMPTOMS: A FIXED, CONSTRICTED PUPIL ____ A DROOPY EYELID ____ LOSS OF FOREHEAD SWEATING ____ as sympathetic ____ innervation of the ____ and ____ branches of the ophthalmic artery is lost

``` (miosis) (partial ptosis) (anhydrosis) sudomotor supraorbital supratrochlear ```