cranial nerves.pdfl

8/13/2019 Cranial Nerves.pdfl

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Neurologic examinationCRANIAL NERVES


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&e olfactory nerve is a s"ecial afferent cranial nerve com"ose!of sensory fiers only2

Its sole function is to !iscern smells2 Olfaction !e"en!s on t&e integrity of t&e olfactory neurons in t&e

roof of t&e nasal cavity an! t&eir connections t&roug& t&e

olfactory ul$ tract$ an! stria to t&e olfactory cortex of t&e me!ial

frontal an! tem"oral loes2

Cranial Nerves Exam

To test olfaction:

2 An o!orant$ suc& as concentrate! vanilla$ "erfume or

coffee$ is "resente! to eac& nostril in turn2

#2 &e "atient is as3e! to sniff (4it& eyes close!) an!i!entify eac& smell2

Olfaction is frequently not tested because of unreliable

patient responses and lack of objective signs.

CRANIAL NERVE I (OL,ACOR5 NERVE)


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Cranial Nerve


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&e o"tic nerve contains s"ecial sensory afferent fiers t&at convey visual information from t&e retina to t&e

occi"ital loe via t&e visual "at&4ay2Evaluation gives im"ortant information aout t&e

nerves$ o"tic c&iasm$ tracts$ t&alamus$ o"tic ra!iations$

an! visual cortex2CN 2 is also the afferent limb of the pupillary light reflex.The optic nerve is tested in the office by visual acuity

measurement, color vision testing, pupil evaluation, visual field

testing, and optic nerve evaluation via ophthalmoscopy and/orstereo biomicroscopy.

Cranial Nerves Exam

CRANIAL NERVE (O6IC NERVE)


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II - OpticExamine t&e O"tic ,un!i
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est Visual Acuity

Allo the patient to use their glasses if available. !ou are

interested in the patient"s best corrected vision2 #osition the patient 2$ feet in front of the %nellen eye

chart &or hold a 'osenbaum poc(et card at a )* inch+reading+ distance.

-ave the patient cover one eye at a time ith a card. As( the patient to read progressively smaller letters until

they can go no further. 'ecord the smallest line the patient read successfully

&2$/2$, 2$/$, etc. 'epeat ith the other eye.


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There are hand held cards that loo( li(e %nellen Charts but are positioned

)* inches from the patient. These are used simply for convenience. Testing

and interpretation are as described for the %nellen.

-and held visual acuity card


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Screen Visual ,iel!s y Confrontation

. %tand to feet in front of the patient and have them loo(

into your eyes.

*. -old your hands about one foot aay from the patient"s

ears, and iggle a finger on one hand.

. As( the patient to indicate hich side they see the finger

move.

0. 'epeat to or three times to test both temporal fields.

1. f an abnormality is suspected, test the four 3uadrants of

each eye hile as(ing the patient to cover the oppositeeye ith a card.


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est 6u"illary Reactions to Lig&t

. 4im the room lights as necessary.

*. As( the patient to loo( into the distance.

. %hine a bright light obli3uely into each pupil in turn.

0. 5oo( for both the direct &same eye and consensual&other eye reactions.

1. 'ecord pupil si6e in mm and any asymmetry or

irregularity.o

f abnormal, proceed ith the test foraccommodation.


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est 6u"illary Reactions toAccommo!ation

*. -old your finger about )$cm from the patient"s nose.

. As( them to alternate loo(ing into the distance and at

your finger.o 7bserve the pupillary response in each eye.


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The pneumonic8

7S O % 8 L R ' 8 All &e Rest #9

may help remind you hich CN does hat

Superior Oblique CN 4

Lateral Rectus CN 6 All The Rest of the muscles innervated b CN !

CRANIAL NERVE # (OC:LO;OOR NERVE)

CRANIAL NERVE % (ROCLEAR NERVE)

CRANIAL NERVE # (A


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Oserve for 6tosisest Extraocular ;ovements

).%tand or sit to 0 feet in front of the patient.

2.As( the patient to follo your finger ith their eyes

ithout moving their head.

.Chec( ga6e in the six cardinal directions using across or +-+ pattern.

*.#ause during upard and lateral ga6e to chec( for

nystagmus.

.Chec( convergence by moving your finger toard

the bridge of the patient"s nose.est 6u"illary Reactions to Lig&t


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Testing CN III, IV, and VI:

To test the extraocular muscles, have thepatient follow a target through the sixprincipal positions of gaze ("H" pattern).


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Rig&t CN# Lesion> Note "atient?s rig&t eye is !eviate!

laterally an! t&ere is "tosis of t&e li!2


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Rig&t CN# Lesion> &e rig&t "u"il (u""er left "icture) ismore !ilate! t&an t&e left "u"il2


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It@s also 4ort& noting t&at !isor!ers of t&e extra ocular muscles

t&emselves (an! not t&e CN 4&ic& innervate t&em) can also lea! to

im"aire! eye movement2

An exam"le is a "atient 4&o &as suffere! a traumatic left orital inury2 &e

inferior rectus muscle &as ecome entra""e! 4it&in t&e resulting fracture$

"reventing t&e left eye from eing ale to loo3 !o4n4ar!2


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This nerve has both motor and sensory components.

The sensory limb has ma9or branches, each

covering roughly )/ of the face.). 7phthalmic

2. :axillary

. :andibular

CRANIAL NERVE * (RI/E;INAL)


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Assessment of CN " Sensor #unction$

;se a sharp implement &e.g. bro(en ooden handle ofa cotton tipped applicator.

As( the patient to close their eyes so that they receiveno visual cues.

Touch the sharp tip of the stic( to the right and left sideof the forehead, assessing the 7phthalmic branch.

Touch the tip to the right and left side of the chee(area, assessing the :axillary branch.

Touch the tip to the right and left side of the 9a area,

assessing the :andibular branch. The patient should be able to clearly identify hen thesharp end touches their face. 7f course, ma(e surethat you do not push too hard as the face is normally3uite sensitive.



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To assess t!is component:

). #ull out a isp of cotton.

2.


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Assessment of CN " +otor #unction$ #lace your hand on both Temporalis muscles, located

on the lateral aspects of the forehead.

As( the patient to tightly close their 9a, causing themuscles beneath your fingers to become taught. Then place your hands on both :asseter muscles,

located 9ust in front of the Temporo=:andibular 9oints&point here loer 9a articulates ith s(ull.

As( the patient to tightly close their 9a, hich shouldagain cause the muscles beneath your fingers tobecome taught. Then as( them to move their 9a fromside to side, another function of the :asseter.


The motor limb of CN innervates the Temporalis and

:asseter muscles, both important for closing the 9a.


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This nerve innervates many of the muscles of facial expression.

"ssessment is performed as follo#s:

>irst loo( at the patient?s face. t should appear symmetric.@ There should be the same amount of rin(les apparent on

either side of the forehead@ The nasolabial folds should be e3ual@ The corners of the mouth should be at the same height

f there is any 3uestion as to hether an apparent asymmetry ifne or old, as( the patient for a picture for comparison. As( the patient to rin(le their eyebros and then close their eyes

tightly. !ou should not be able to open the patient?s eyelids iththe application of gentle upards pressure. CN 1 controls themuscles that close the eye lids &as opposed to CN , hich

controls the muscles hich open the lid. As( the patient to smile. The corners of the mouth should rise tothe same height and e3ual amounts of teeth should be visible oneither side.

As( the patient to puff out their chee(s. oth sides should puffe3ually and air should not lea( from the mouth.

CRANIAL NERVE + (,ACIAL)


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Testing the facial nerve.The patient wrinkles her foreheadwhile the two sides are compared.Patient tightl shuts eelids while

examiner attempts to pr open.The two sides are compared.Patient smiles and shows her teethwhile the examiner compares thenasola!ial folds on either side.


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,nterpretation$CN 1 has a precise pattern of innervation, hich

has important clinical implications.

The right and left upper motor neurons &;:Ns

each innervate both the right and left loermotor neurons &5:Ns that allo the forehead tomove up and don.

-oever, the 5:Ns that control the muscles of the

loer face are only innervated by the ;:N fromthe opposite side of the face.



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,nterpretation$Thus, in the setting of CN 1 dysfunction, the pattern of

ea(ness or paralysis observed ill differ dependingon hether the ;:N or 5:N is affected.

;:N dysfunction8 This might occur ith a central nervoussystem event, such as a stro(e. n the setting of ';:N CN 1 dysfunction, the patient ould be able torin(le their forehead on both sides of their face, asthe left CN 1 ;:N cross innervates the ' CN 1 5:N

that controls this movement. -oever, the patientould be unable to effectively close their left eye orraise the left corner of their mouth.



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Rig&t central CN+ !ysfunction>

Note preserved ability to rin(le forehead.

5eft corner of mouth, hoever, is slightly loer than right.

5eft nasolabial fold is slightly less pronounced compared ith right.


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,nterpretation$

5:N dysfunction8 This occurs most commonly in the setting

of ell?s #alsy, an idiopathic, acute CN 1 peripheral

nerve palsy. n the setting of ' CN 1 peripheral &5:N

dysfunction, the patient ould not be able to rin(le

their forehead, close their eye or raise the corner oftheir mouth on the right side. 5eft sided function ould

be normal.



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5eft peripheral CN1 dysfunction8

Note loss of forehead rin(le, ability to close eye, ability to raise corner of

mouth, and decreased nasolabial fold prominence on left.


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CN 1 is also responsible for carrying taste

sensations from the anterior 2/ of the tongue.

To test the sensory fibers of the facial nerve,

apply sugar, salt, or lemon 9uice on a cottonsab to the lateral aspect of each side of the

tongue and have the patient identify the taste.

Taste is often tested only hen specific

pathology of the facial nerve is suspected.



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CN B carries sound impulses from the cochlea to the brain.#rior to reaching the cochlea, the sound must firsttraverse the external canal and middle ear.


%tand behind the patient and as( them to close theireyes.


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Beer est

). rasp the )2 -6 tuning for( by the stem and stri(e it against the

bony edge of your palm, generating a continuous tone.

Alternatively you can get the for( to vibrate by +snapping+ the

ends beteen your thumb and index finger.

*. -old the stem against the patient?s s(ull, along an imaginaryline that is e3uidistant from either ear.

. The bones of the s(ull ill carry the sound e3ually to both the

right and left CN B. oth CN Bs, in turn, ill transmit the

impulse to the brain.

D. The patient should report hether the sound as heard e3ually

in both ears or better on one side then the other &referred to as laterali6ing to a side.

CRANIAL NERVE - (ACO:SIC)


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Beer est



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Rinne est>


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Rinne est>



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,nterpretation$ The above testing is reserved for those instances hen a patient

complains of a deficit in hearing. Thus, on the basis of history, thereshould be a complaint of hearing decline in one or both ears.

n the setting of a conductive hearing loss &e.g. ax in the external canal,the


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,nterpretation$

n the setting of conductive hearing loss, bone conduction &Cill be better then air conduction &AC hen assessed by the'inne Test. f there is a bloc(age in the passageay &e.g. axthat carries sound from the outside to CN B, then sound ill bebetter heard hen it travels via the bones of the s(ull. Thus, thepatient ill note C to be better then or e3ual to AC in the earith the sub9ective decline in hearing.

n the setting of a sensorineural hearing loss, air conduction illstill be better then bone conduction &i.e. the normal pattern ill beretained. This is because the problem is at the level of CN B.Thus, regardless of the means &bone or air by hich the impulsegets to CN B, there ill still be a mar(ed hearing decrement in theaffected ear. As AC is normally better then C, this ill still be the

case.



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Summar$ dentifying conductive vs sensorineural hearing deficits

re3uires historical information as ell as the results of


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These nerves are responsible for raising the soft palate ofthe mouth and the gag reflex, a protective mechanismhich prevents food or li3uid from traveling into thelungs. As both CNs contribute to these functions, theyare tested together.

Testing Elevation of t!e soft palate: As( the patient to open their mouth and say, Eahhhh,F

causing the soft palate to rise upard. 5oo( at the uvula, a midline structure hanging don

from the palate. f the tongue obscures your vie, ta(ea tongue depressor and gently push it don and out ofthe ay.

The ;vula should rise up straight and in the midline.

CRANIAL NERVE . (/LOSSO6AR5N/EAL)

CRANIAL NERVE 10 (VA/:S)


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Normal Oro"&arynx




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,nterpretation$

f CN D on the right is not functioning, the uvula ill be pulled to the left.




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5eft peritonsillar abscess8 infection ithin left tonsil has

pushed uvula toards the right.




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Testin' the -a' Refle.$ As( the patient to idely open their mouth. f you are

unable to see the posterior pharynx &i.e. the bac( oftheir throat, gently push don ith a tonguedepressor.

n some patients, the tongue depressor alone ill elicita gag. n most others, additional stimulation isre3uired. Ta(e a cotton tipped applicator and gentlybrush it against the posterior pharynx or uvula. Thisshould generate a gag in most patients.

A small but measurable percent of the normalpopulation has either a minimal or non=existent gagreflex. #resumably, they ma(e use of othermechanisms to prevent aspiration.




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ag testing is rather noxious. %ome people are particularly sensitive to evenminimal stimulation. #erform this test hen there is reasonable suspicionthat pathology exists.

This ould include to ma9or clinical situations8 f you suspect that the patient has suffered acute dysfunction, most

commonly in the setting of a stro(e. These patients may complain ofcough hen they sallo. 7r, they may suffer from recurrentpneumonia. oth of these events are signs of aspiration of food contentsinto the passageays of the lungs. These patients may also have othercranial nerve abnormalities as lesions affecting CN D and )$ often affectCNs )) and )2, hich are anatomically nearby.

#atient?s suffering from sudden decreased level of consciousness. n this

setting, the absence of a gag might indicate that the patient is no longerable to reflexively protect their airay from aspiration. %trongconsideration should be given to intubating the patient, providing themith a secure mechanical airay until their general condition improves.




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CN D is also responsible for taste originating on the

posterior )/ of the tongue.

CN )$ also provides parasympathetic innervation to theheart, though this cannot be easily tested on physical

examination.




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CN )) innervates the muscles hich permit shrugging ofthe shoulders &Trape6ius and turning the headlaterally &%ternocleidomastoid.


#lace your hands on top of either shoulder and as( thepatient to shrug hile you provide resistance.4ysfunction ill cause ea(ness/absence ofmovement on the affected side.

#lace your open left hand against the patient?s right

chee( and as( them to turn into your hand hile youprovide resistance. Then repeat on the other side. Theright %ternocleidomastoid muscle causes the head toturn to the left, and vice versa.

CRANIAL NERVE 11 (S6INAL ACCESSOR5)


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CN )2 is responsible for tongue movement.

Gach CN )2 innervates one=half of the tongue.

"ssessment is performed as follo#s: As( the patient to stic( their tongue straight out of their

mouth.

f there is any suggestion of deviation to one

side/ea(ness, direct them to push the tip of their

tongue into either chee( hile you provide counterpressure from the outside.

CRANIAL NERVE 1 (56O/LOSSAL)


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,nterpretation$ f the right CN )2 is dysfunctional, the tongue ill deviate

to the right. This is because the normally functioning lefthalf ill dominate as it no longer has opposition from the

right. %imilarly, the tongue ould have limited or absentability to resist against pressure applied from outside theleft chee(.



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5eft CN )2 4ysfunction8 %tro(e has resulted in 5 CN )2 #alsy.

Tongue therefore deviates to the left.



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!duction,phsiologic"H"

#ateral rectusmuscle

$otor%&!ducens

'lenchawpalpate,light touchcomparison

*calp, conunctiva,teeth

*ensor%Trigeminal

'orneal reflex$uscles ofmastication

$otor%Trigeminal

Phsiologic"H"

*uperior o!li+uemuscle

$otor&%Trochlear

Phsiologic"H" and near

pointresponse

pper lid elevation,extraocular eemovement, pupil

constriction,accommodation

$otor&&&-culomotor

%isual acuit,fields, color,nerve head

%ision*ensor&&-ptic

&dentif odors*mell*ensor&-lfactor

Test(s)PrimaryFunction(s)

Innervation(s)

Number

CranialNerve

*mile puff


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Tonguedeviation

$uscles of tongue$otor&&Hpoglossal

*hrug, headturn againstresistance

*ternomastoid andtrapezius muscles

$otor&ccessor

#arnx, trachea, esophagus*ensor%agus

/ag reflexPharnx, tongue, larnx,thoracic and a!dominalviscera

$otor%agus

Taste0posterior one third oftongue

*ensor&/lossopharngeal

/ag reflexTongue and pharnx$otor&

/lossopharnge

al

1inne test forhearing,2e!er test for!alance

Hearing and !alance*ensor%&&&%esti!ulocochlear

Taste0anterior two thirds oftongue

*ensor%&&3acial

*mile, puffcheeks,wrinkleforehead, propen closed

lids

$uscles of facial expression$otor%&&3acial


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cranial nerves.pdfl

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