Cranial Nerves and Its Examination

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Cranial nerves and its

examination


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Components of nervous system


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Names of cranial nerves


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Classification Sensory cranial nerves: contain only afferent (sensory) fibers

I Olfactory nerve

II Optic nerve

VIII Vestibulocochlear nerve

Motor cranial nerves: contain only efferent (motor) fibers III Oculomotor nerve

IV Trochlear nerve VI Abducent nerve

XI Accessory nerve

XII Hypoglossal nerve

Mixed nerves: contain both sensory and motor fibers--- V Trigeminal nerve,

VII Facial nerve,

IX Glossopharyngeal nerve

X Vagus nerve


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Human Anatomy, Frolich, Head/Neck IV: Cranial Nerves

Special Sense NervesI,II,VIII

Somatic Motor Nerves

EyeIII,IV,VITongueXII

Face and jaws

VII, VRest of body nerves

IX,X,XI


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Nomenclature

Somatic - Relating to the skeleton or skeletal

(voluntary) muscle.

Visceral Relating to (involuntary) muscle and its

(autonomic) innervation. An organ of the digestive,

cardiac, respiratory, urogenital, and endocrine

systems.


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Special Relating to special sense

organs (smell, vision,equilibrium and

hearing)

Afferent incoming,sensory

Efferent Outgoing, motor


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Functional components

General somatic afferent fibers (GSA): transmitexteroceptive and proprioceptive impulses fromhead and face to somatic sensory nuclei (V)

General somatic efferent fibers (GSE): innervateskeletal muscles of eye and tongue (III, IV, VI, XII)


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General visceral afferent fibers (GVA):transmit interoceptive impulses from theviscera to the visceral sensory nuclei (VII,IX, X)

General visceral efferent fibers (GVE):transmit motor impulses from the generalvisceral motor nuclei and relayed in

parasympathetic ganglions. Thepostganglionic fibers supply cardiacmuscles smooth muscles and glands(III,VII,IX, X)


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Specialcomponents

Special visceral afferent fibers (SVA): transmit sensoryimpulses from special sense organs of smell and taste to thebrain (VII, IX, X,I)

Special somatic afferent fibers (SSA): transmit sensory

impulses from special sense organs of vision, equilibriumand hearing to the brain (VIII)


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Special visceral efferent fibers (SVE):

transmit motor impulses from the brain to

skeletal muscles derived from brachial

arches of embryo. These include themuscles of mastication, facial expression

and swallowing (V, VII, IX, X, XI)


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General concept

Motor nuclei send fibers directly to

muscles

Nuclei for cardiac, visceral and glands

send fibers to autonomic ganglion for

relay.

Sensory nuclei cell bodies of second

neuron, first neurons are outside CNS in

the gaglion.


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The central process of the cells in the

nuclei go to three sensory destination

1. Motor nuclei for reflex

2. Cerebellum

3. Opposite thalamus for relay in sensory

cortex.


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I. Olfactory nerve

-is a special visceral

afferent (SVA) nerve

that mediates the

sense of smell(olfaction).

the only cranial nerve

that projects directly

to the forebrain


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Enter the bulb to synapse on mitral

cells.

The central processe pass in the

olfactory tract to anterior perforatedsubstance and uncus

The olfactory system consists of the

olfactory epithelium, bulbs and tractsalong with olfactory areas of the

brain collectively known as the

rhinencephalon


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Clinical correlation- CN I damage

-results in anosmia, loss of olfactory

sensation


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II.Optic nerve

special somatic afferent

nerve

Arises from the retina of the

eye Optic nerves pass through

the optic canals and

converge at the optic chiasm

Lateral geniculate body

relay and sorting station.


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Clinical correlations-CN II

-When it is transected, ipsilateral blindness and

loss of direct pupillary light reflex result;

regeneration of the optic nerve does not occur. -When it is subjected to increased intracranial

pressure (e.g., tumor), papilledema, a "choked"

optic disk results.

When it is constricted, optic atrophy (i.e., axonal

degeneration) results.


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III. Occulomotor

contains general somatic efferent and

general visceral efferent fibers.

Is a pure motor nerve that moves the eye,

constricts the pupil, Accommodates and

converges.


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III.Occulomotor

NUCLIE

Nucleus of oculomotor

Motor to superior, inferior and medial recti; inferiorobliquus; levator palpebrae superioris

Accessory nucleus of oculomotor(Edinger- Westphal)

Parasympathetic to sphincter pupillea and ciliary muscle

Leaves the skull through - Superior orbital fissure


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Ciinical correlations-CN III

1. Oculomotor paralysis is seen frequently with

transtentorial herniation (subdural, epidural

hematoma).

-results in diplopia (double vision) when thepatient looks in the direction of the paretic

muscle.

Results on ptosis, loss of accomodation and

dilatation of pupil.


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IV.Trochlear

Is a pure GSE nerve that innervates the

superior oblique muscle,which

depresses, intorts, and abducts the eye.

Nuclei - trochlear nucleus of the

midbrain.

Passes through the lateral wall of the

cavernous sinus,

Leaves the skull - superior orbital fissure.


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Clinical correlations

CN IV paralysis

results in the following

conditions:

1. Extorsion of the

eye and weakness ofdownward gaze

2. Vertical diplopia,

which increases when

looking down


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V. Trigeminal nerve

Components of fibers SVE fibers: originate from motor nucleus of

trigeminal nerve, and supply masticatorymuscles

GSA fibers: transmit facial sensation tosensory nuclei of trigeminal nerve, the GSAfibers have their cell bodies in trigeminal

ganglion, which lies on the apex of petrouspart of temporal bone


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Nuclei

One motor and three sensory

Motor

Masticatory muscle, mylohyoid, tensor palati

Sensory

1. Mesencephalic Propioception for muscle of

mastication, face, tongue, orbit

2. Main sensory Touch from trigeminal area3. Spinal nucleus Pain and temprature from

trigeminal area


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Branches

Ophthalmic nerve (V1,sensory) leave the skull

through the superior orbitalfissure, to enter orbital cavity

Branches

Frontal nerve:

Supratrochlear nerve

Supraorbital nerve

Lacrimal nerve

Nasociliary nerve


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Maxillary nerve(V2, sensory)

Leave skull through

foramen rotundum

Branches

Infraorbital nerve Zygomatic nerve

Superior alveolar

nerve

Pterygopalatine

nerve


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Distribution:

Sensation from cerebral

dura mater Maxillary teeth

Mucosa of nose andmouth

Skin between eye andmouth


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Mandibular nerve(V3,mixed)

Leave the skull through the

foramen ovale to enter the

infratemporal fossa

Branches

Main trunk nervous spinosusand nerve to medial pterygoid

Anterior trunk buccal nerve,

nerve to massticatory muscles.

Posterior trunk auricuotemporal, lingual, inferior

alveolar.


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Distribution:

Sensation from cerebral dura mater

Teeth and gum of lower jaw

Mucosa of floor of mouth

Anterior 2/3 of tongue

Skin of auricular and temporal

regions and below the mouth

Motor to masticatory muscles,

mylohyoid, and anterior belly of

digastric

Parotid gland sensory throughauriculotemporal nerve


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Clinical correlations-lesions of

CN V

1. Loss of general sensation from the face

and mucous membranes of the oral and

nasal cavities

2. Loss of the corneal reflex

4. Deviation of the jaw to the weak side,

due to the unopposed action of the

opposite lateral pterygoid muscle


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VI Abd t


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VI Abducent Fibers leave the inferior pons and enter the orbit

via the superior orbital fissure

Arises from the abducent nucleus of the caudalpons

Primarily a motor nerve innervating the lateralrectus muscle (abducts the eye; thus the name

abducent)


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Clinical correlations-CN VI

paralysis

Is the most common isolated muscle palsy.

Results in the following conditions:

1. Convergent strabismus (esotropia), with the

inability to abduct the eye due to the unopposed

action of the medial rectus muscle

2. Horizontal diplopia, with maximum separationof the double when looking toward the paretic

lateral rectus muscle


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Facial nerve (V)Components of fibers

SVE fibers originate from nucleus of facial nerve, and supply

facial muscles

GVE fibers derived from superior salivatory nucleus and relayed

in pterygopalatine ganglion and submandibular ganglion. The

postganglionic fibers supply lacrimal, submandibular and

sublingual glands

SVA fiber from taste buds of anterior two-thirds of tongue which

cell bodies are in the geniculate ganglion of the facial nerve and

end by synapsing with cells of nucleus of solitary tract

GSAfibers from skin of external ear


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Course: leaves skull through

internal acoustic meatus,

facial canal and

stylomastoid foramen, it

then enters parotid gland

where it divides into five

branches which supply facial

muscles


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Branches within the facial canal Chorda tympani :joins lingual branch of mandibular

nerve

To taste buds on anterior two-thirds of tongue

Relayed in submandibular ganglion, the

postganglionic fibers supply submandibular and

sublingual glands

Greater petrosal nerve: GVE fibers pass to

pterygopalatine ganglion and there relayed through thezygomatic and lacrimal nerves to lacrimal gland

Stapedial nerve : to stapedius


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Branches outside of facial canal

Temporal

Zygomatic

Buccal

Marginal mandibular

Cervical


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Clinical correlations-lesions ofCN VII

1. Flaccid paralysis of the muscles of facialexpression (upper and lowl face)

2. Loss of the corneal (blink) reflex (efferent

limb), which may leads corneal ulceration(keratitis paralytica)

3. Loss of taste (ageusia) from the anterior

two-thirds of the tongue4. Hyperacusis (increased acuity to sounds),due to stapedius paralysis


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5. Bell palsy - vis caused by trauma to the nervewithin the facial canal. It is a lower motor neuron(LMN) lesion with paralysis of all muscles offacial expression.

6. Central facial palsy- (supranuclear palsy)(UMN).

-results in contralateral facial weakness belowthe orbit.

-frontalis and orbicularis occuli escape due tobilateral representation in cerebral cortex


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7. Crocodile tears syndrome (lacrimationduring eating) is caused by a facialnerve lesion proximal to the geniculate

ganglion. Regenerating 'preganglionic salivatory

fibers are misdirected to the

pterygopalatine ganglion, which projectsto the lacrimal gland.

C i l N VIII


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Cranial Nerve VIII:

Vestibulocochlear Two divisions cochlear (hearing) and

vestibular (balance)

Functions are solely sensory equilibrium and

hearing Fibers arise from the hearing and equilibrium

apparatus of the inner ear, pass through the

internal acoustic meatus, and enter the

brainstem at the pons-medulla border


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Cranial Nerve VIII: Vestibulocochlear

Figure VIII from Table 13.2


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Clinical correlation

lesions of the vestibular nerve

-result in disequilibrium, vertigo, and

nystagmus.

lesions of the cochlear nerve

-result in hearing loss (sensorineural

deafness)

-cause tinnitus (irritative lesions).


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Glossopharyngeal nerve (IX)

Components of fibers SVEfibers: originate from nucleus ambiguus, and

supply stylopharygeus

GVE fibers: arise from inferior salivatory nucleus

and ralyed in otic ganglion, the postganglionic fiberssupply parotid gland (secretomotor)

SVA fibers: arise from the cells of inferior ganglion,the central processes of these cells terminate innucleus of solitary tract, the peripheral processessupply the taste buds on posterior third of tongue


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GVA fibers: visceral sensation from mucosa

of posterior third of tongue, pharynx,

auditory tube and tympanic cavity, carotid

sinus, and end by synapsing with cells ofnucleus of solitary tract

GSA fibers: sensation from skin of posterior

surface of auricle


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Course: leaves the skull via jugular foramen

Branches

Lingual branches : to taste buds and mucosa ofposterior third of tongue

Pharyngeal branches : take part in forming the

pharyngeal plexus

Tympanic nerve : GVE fibers via tympanic and lesser

petrosal nerves to otic ganglion, with postganglionic

fibers via auriculotemporal ( 3) to parotid gland

Carotid sinus branch : innervations to carotid sinus

Others: tonsillar and stylophayngeal branches


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Cli i l l ti l i f


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CN IX

1. Loss of the gag (pharyngeal) reflex

2. Loss of the carotid sinus reflex

3. Loss of taste from the posterior third ofthe tongue

4. Glossopharyngeal neuralgia


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Vagus nerve (X)components of fibers

GVE fibers: originate from dorsal nucleus of vagusnerve, synapse in parasympathetic ganglion, shortpostganglionic fibers innervate cardiac muscles,smooth muscles and glands of viscera

SVE fibers: originate from ambiguus, to muscles ofpharynx and larynx

GVA fibers: carry impulse from viscera in neck,thoracic and abdominal cavity to nucleus of solitarytract

GSA fiber: sensation from auricle, external acousticmeatus and cerebral dura mater


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Branches in neck

Superior laryngeal nerve:

Internal branch, which pierces thyrohyoid

membrane to innervates mucous membrane of

larynx above fissure of glottis

External branch, which innervates cricothyroid

Cervical cardiac branches : descending to

terminate in cardiac plexus

Others: auricular, pharyngeal and meningeal

branches


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Branches in thorax

Recurrent laryngeal nerves

Right one hooks around right

subclavian artery, left one hooks

aortic arch

Both ascend in tracheo-esophageal

groove

Innervations: laryngeal mucosa

below fissure of glottis , all laryngeal

muscles except cricothyroid

Bronchial and esophageal branches


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Branches in

abdomen

Anterior and posteriorgastric branches

supply pyloric part

Hepatic branches:

supply liver and

gallbladder

Celiac branches:

sympathetic fibers to

liver, pancreas, spleen,

kidneys, intestine


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Clinical correlations lesions of


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CN X

1. Ipsilateral paralysis of the soft palate,pharynx, and larynx leading to dysphonia

(hoarseness), dyspnea, dysarthria, anddysphagia

2. Loss of the gag (palatal) reflex

3. Anesthesia of the pharynx and larynx,leading to unilateral loss of the coughreflex


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XI Accessory

Mediates head and shoulder movement andinnervates laryngeal muscles.

1. Cranial division

-arises from the nucleus ambiguus of the medulla.

--exits the medulla and joins the vagal nerve --exits the skull via the jugular foramen with CN IX

and CN X.

-innervates the intrinsic muscles of the larynx via

the inferior (recurrent) laryngeal nerve, with theexception of the cricothyroid muscle.


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2. Spinal division

-arises from the ventral horn of cervical segments

CI-C6.

-Spinal roots exit the spinal cord laterally betweenthe ventral and dorsal spinal roots, ascend through

the foramen magnum, and exit skull via the jugular

foramen.

-innervates the sternocleidomastoid (with C2) andtrapezius rn cles (with C3 and C4


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Clinical correlations lesions of


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Clinical correlations - lesions of

CN XI

1. Paralysis of the sternocleidomastoid muscle

-results in difficulty in turning the head to the side

opposite the lesion.

2. Paralysis of the trapezius muscle-results in a shoulder droop.

-results in the inability to shrug the ipsilateral

shoulder.3. Paralysis of the larynx occurs if the cranial root

is involved


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Hypoglossal Nerve (CN XII)

A. General characteristics-CN XII

-mediates tongue movement.

-arises from the hypoglossal nucleus of

the medulla.

-exits the skull via the hypoglossal canal. -innervates intrinsic and extrinsic muscles

of the tongue except palatoglossus .


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B Clinical correlations CN XII


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B. Clinical correlations-CN XII

-When it is transected, hemiparalysis of

the tongue results.

-When it is protruded, the tongue points

toward the weak side due to theunopposed action of the opposite

genioglossus muscle

Terminal nerve or Cranial nerve


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Terminal nerve orCranial nerve

zero

It was first found in humans in1913, although its presence in humansremains controversial.

However, a study has indicated that theterminal nerve is a common finding in theadult human brain.

It projects from the nasal cavity, enters the

brain as a microscopic plexus ofunmyelinated peripheral nerve fascicles.


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The nerve is often overlooked in autopsies because itis unusually thin for a cranial nerve, and is often tornout upon exposing the brain. Careful dissection isnecessary to visualize the nerve

It is very close to and often confused for a branch ofthe olfactory nerve, This fact suggests that the nerve iseither vestigial or may be related to the sensingof pheromones.

The nerve zero projects to the medial and lateral septal

nuclei, and the preoptic areas all of which are involvedin regulating sexual behavior in mammals.


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Neurologic examinationCRANIAL NERVES

Cranial Nerves Exam


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Olfaction depends on the integrity of the olfactory neurons in the

roof of the nasal cavity and their connections through the

olfactory bulb, tract to the olfactory cortex

To test olfaction:

1. An odorant, such as concentrated vanilla, perfume or coffee,

is presented to each nostril in turn.

2. The patient is asked to sniff (with eyes closed) and identifyeach smell.

Olfaction is frequently not tested because of unreliable patient

responses and lack of objective signs.

CRANIAL NERVE I (OLFACTORY NERVE)

Cranial Nerve I


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Cranial Nerve I

Cranial Nerves Exam


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Evaluation gives important information about the nerves,

optic chiasm, tracts, thalamus, optic radiations, and visual

cortex.CN 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

CRANIAL NERVE 2 (OPTIC NERVE)

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II - Optic

Examine the Optic Fundi
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Test Visual Acuity

1. Allow the patient to use their glasses if available. You are

interested in the patient's best corrected vision.

2. Position the patient 20 feet in front of the Snellen eye

chart3. Have the patient cover one eye at a time with a card.

4. Ask the patient to read progressively smaller letters until

they can go no further.

5. Record the smallest line the patient read successfully

Repeat with the other eye.


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There are hand held cards that look like Snellen Charts but are positioned

14 i h f th ti t Th d i l f i T ti


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

and interpretation are as described for the Snellen.

Hand held visual acuity card


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Screen Visual Fields

1. Stand two feet in front of the patient and have them lookinto your eyes.

2. Hold your hands about one foot away from the patient's

ears, and wiggle a finger on one hand.

3. Ask the patient to indicate which side they see the finger

move.

4. Repeat two or three times to test both temporal fields.

5. If an abnormality is suspected, test the four quadrants of

each eye while asking the patient to cover the opposite

eye with a card.


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Test Pupillary Reactions toAccommodation

Hold your finger about 10cm from the patient's nose.

Ask them to alternate looking into the distance and at

your finger.

Observe the pupillary response in each eye.


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The pneumonic:

S O 4 L R 6 All The Rest 3may help remind you which CN does what

CRANIAL NERVE 3 (OCULOMOTOR NERVE)

CRANIAL NERVE 4 (TROCHLEAR NERVE)

CRANIAL NERVE 6 (ABDUCENS NERVE)


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Observe for Ptosis

Test Extraocular Movements1.Stand or sit 3 to 6 feet in front of the patient.

2.Ask the patient to follow your finger with their eyes

without moving their head.

3.Check gaze in the six cardinal directions using a

cross or "H" pattern.

4.Pause during upward and lateral gaze to check for

nystagmus.

5.Check convergence by moving your finger toward

the bridge of the patient's nose.Test Pupillary Reactions to Light


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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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Right CN3 Lesion: Note patient's right eye is deviated

laterally and there is ptosis of the lid.


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Right CN3 Lesion: The right pupil (upper left picture) is

more dilated than the left pupil.


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CRANIAL NERVE 5 (TRIGEMINAL)


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Assessment of CN 5 Sensory Function:

Use a sharp implement Ask the patient to close their eyes so that they

receive no visual cues. Touch the sharp tip of the stick to the right and

left side of the forehead, assessing theOphthalmic branch. Touch the tip to the right and left side of the

cheek area, assessing the Maxillary branch.

Touch the tip to the right and left side of thejaw area, assessing the Mandibular branch. The patient should be able to clearly identify

when the sharp end touches their face.




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To assess this component:

1. Pull out a wisp of cotton.

2. While the patient is looking

straight ahead, gently brushthe wisp against the lateralaspect of the sclera (outerwhite area of the eye ball).

3. This should cause the patient toblink.

Blinking also requires that CN 7function normally, as itcontrols eye lid closure.


The Ophthalmic branch of CN 5 also receives sensory input

from the surface of the eye.



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Assessment of CN 5 Motor Function:

Place your hand on both Temporalis muscles, located onthe lateral aspects of the forehead.

Ask the patient to tightly close their jaw, causing themuscles beneath your fingers to become taught.

Then place your hands on both Masseter muscles.

Ask the patient to tightly close their jaw, which should againcause the muscles beneath your fingers to become taught.Then ask them to move their jaw from side to side, functionof lateral and medial pterygoid


The motor limb of CN 5 innervates the Temporalis and

Masseter muscles, both important for closing the jaw.



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CRANIAL NERVE 7 (FACIAL)


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This nerve innervates muscles of facial expression.

Assessment is performed as follows: First look at the patients face. It should appearsymmetric.

There should be the same amount ofwrinkles apparent on either side of theforehead

The nasolabial folds should be equal The corners of the mouth should be at the

same height

If there is any question as to whether anapparent asymmetry if new or old, ask thepatient for a picture for comparison.



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Interpretation:

CN 7 has a precise pattern of innervation, whichhas important clinical implications.

The right and left upper motor neurons (UMNs)

each innervate both the right and left lowermotor neurons (LMNs) that allow the forehead tomove up and down.

However, the LMNs that control the muscles of the

lower face are only innervated by the UMN fromthe opposite side of the face.


Central Facial Paralysis (Central Seven)


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caused by a lesion of the corticonuclear (corticobulbar) tract above thelevel of the facial nucleus (upper motor neuron lesion)

causes paralysis/paresis of the muscles of the contralateral lower face upper part of facial nucleus contains motor neurons that innervatemuscles of upper face it is innervated by ipsilateral and contralateralcorticonuclear fibers unilateral lesion of corticonuclear tract does notaffect muscles of upper face on either side

lower part of facial nucleus contains motor neurons that innervatemuscles of lower face it is innervated only by contralateralcorticonuclear fibers unilateral lesion of corticonuclear tract (abovethe level of facial nucleus) affects muscles of lower face on opposite sideof lesion


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Textbook Fig. 25-14


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Right central CN7 dysfunction:

Note preserved ability to wrinkle forehead.

Left corner of mouth, however, is slightly lower than right.

Left nasolabial fold is slightly less pronounced compared with right.


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Interpretation:

LMN dysfunction: This occurs most commonly in the settingof Bells Palsy, an idiopathic, acute CN 7 peripheral

nerve palsy. In the setting of R CN 7 peripheral (LMN)

dysfunction, the patient would not be able to wrinkle

their forehead, close their eye or raise the corner oftheir mouth on the right side. Left sided function would

be normal.

( )


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Left peripheral CN7 dysfunction:

Note loss of forehead wrinkle, ability to close eye, ability to raise corner of

mouth, and decreased nasolabial fold prominence on left.


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Left peripheral CN7 dysfunction:

Note loss of forehead wrinkle, ability to close eye, ability to raise corner of

mouth, and decreased nasolabial fold prominence on left.


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CRANIAL NERVE 8 (ACOUSTIC)


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CN 8 carries sound impulses from the cochlea to the brain.

Prior to reaching the cochlea, the sound must firsttraverse the external canal and middle ear.

Assessment is performed as follows: Stand behind the patient and ask them to close their

eyes. Whisper a few words from just behind one ear. The

patient should be able to repeat these back accurately.Then perform the same test for the other ear.

Alternatively, place your fingers approximately 5 cmfrom one ear and rub them together. The patientshould be able to hear the sound generated. Repeatfor the other ear.



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These tests are rather crude. Precisequantification, generally necessary whenever

there is a subjective decline in acuity

Hearing is broken into 2 phases: conductive andsensorineural.

The conductive phase refers to the passage of

sound from the outside to the level of CN 8. This

includes the transmission of sound through theexternal canal and middle ear.


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Sensorineural refers to the transmission ofsound via CN 8 to the brain.

Identification of conductive (a much more

common problem in the generalpopulation) defects is determined as

follows:



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Weber Test

1. Grasp the 512 Hz tuning fork by the stem and strike it against the

bony edge of your palm, generating a continuous tone.

2. Hold the stem against the patients skull, along an imaginary

line that is equidistant from either ear.

3. The bones of the skull will carry the sound equally to both the

right and left CN 8. Both CN 8s, in turn, will transmit theimpulse to the brain.

4. The patient should report whether the sound was heard equally

in both ears or better on one side then the other (referred to as

lateralizing to a side).



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Weber Test

CRANIAL NERVE 8 (ACOUSTIC) Webber test


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Interpretation: In the setting of a conductive hearing loss (e.g. wax in the

external canal), the Webber test will lateralize (i.e. sound will beheard better) in the ear that has the subjective decline inhearing. This is because when there is a problem withconduction, competing sounds from the outside cannot reachCN 8via the external canal. Thus, sound generated by thevibrating tuning fork and traveling to CN 8 by means of bonyconduction is better heard as it has no outside competition.

In the setting of a sensorineural hearing loss (e.g. a tumor ofCN 8), the Webber test will lateralize to the ear which does nothave the subjective decline in hearing. This is because CN 8 isthe final pathway through which sound is carried to the brain.Thus, even though the bones of the skull will successfully transmitthe sound to CN 8, it cannot then be carried to the brain due to

the underlying nerve dysfunction.



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1. Grasp the 512 Hz tuning fork by the stem and strike itagainst the bony edge of your palm, generating acontinuous tone.

2. Place the stem of the tuning fork on the mastoid bone,

The vibrations travel via the bones of the skull to CN 8,allowing the patient to hear the sound.

3. Ask the patient to inform you when they can no longerappreciate the sound. When this occurs, move thetuning fork such that the tines are placed right next to

(but not touching) the opening of the ear. At this point,the patient should be able to again hear the sound. Thisis because air is a better conducting medium thenbone.

Rinne Test:



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Rinne Test:



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Rinne Test:


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Summary:

First determine by history and crude acuity testingwhich ear has the hearing problem.

Perform the Webber test. If there is a conductivehearing deficit, the Webber will lateralize to the

affected ear. If there is a sensorineural deficit, theWebber will lateralize to the normal ear.

Perform the Rinne test. If there is a conductive hearingdeficit, BC will be greater then or equal to AC in theaffected ear. If there is a sensorineural hearing deficit,

AC will be greater then BC in the affected ear.

CRANIAL NERVE 9 (GLOSSOPHARYNGEAL)

CRANIAL NERVE 10 (VAGUS)


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

Testing Elevation of the soft palate:

Ask the patient to open their mouth and say, ahhhh,causing the soft palate to rise upward.

Look at the uvula.

The Uvula should rise up straight and in the midline.





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Normal Oropharynx





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Interpretation:

If CN 9 on the left is not functioning, the uvula will be pulled to the right.

C 0 ( GUS)




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Left peritonsillar abscess: infection within left tonsil has

pushed uvula towards the right.





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Testing the Gag Reflex: Ask the patient to widely open their mouth. If

you are unable to see the posterior pharynx(i.e. the back of their throat), gently push down

with a tongue depressor. In some patients, the tongue depressor alone

will elicit a gag. In most others, additionalstimulation is required. Take a cotton tipped

applicator and gently brush it against theposterior pharynx or uvula. This shouldgenerate a gag in most patients.





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CN 9 is also responsible for taste originating on the

posterior 1/3 of the tongue.

CN 10 also provides parasympathetic innervation to the

heart, though this cannot be easily tested on physical

examination.


CRANIAL NERVE 11 (SPINAL ACCESSORY)


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CN 11 innervates the muscles which permit shrugging of

the shoulders (Trapezius) and turning the headlaterally (Sternocleidomastoid).

Assessment is performed as follows: Place your hands on top of either shoulder and ask the

patient to shrug while you provide resistance.Dysfunction will cause weakness/absence ofmovement on the affected side.

Place your open left hand against the patients rightcheek and ask them to turn into your hand while you

provide resistance. Then repeat on the other side. Theright Sternocleidomastoid muscle causes the head toturn to the left, and vice versa.



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CRANIAL NERVE 12 (HYPOGLOSSAL)


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CN 12 is responsible for tongue movement.Each CN 12 innervates one-half of the tongue.

Assessment is performed as follows:

Ask the patient to stick their tongue straight out of theirmouth.

If there is any suggestion of deviation to one

side/weakness, direct them to push the tip of their

tongue into either cheek while you provide counterpressure from the outside.



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Interpretation: If the right CN 12 is dysfunctional, the tongue will deviate

to the right. This is because the normally functioning lefthalf will dominate as it no longer has opposition from theright. Similarly, the tongue would have limited or absent

ability to resist against pressure applied from outside theleft cheek.



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Left CN 12 Dysfunction: Stroke has resulted in L CN 12 Palsy.

Tongue therefore deviates to the left.


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Testing the hypoglossal nerve.Patient is instructed to stick out the tongueand then move it laterally against resistance.

Cranial Nerve Number Innervation(s) PrimaryF i ( )

Test(s)

Summary


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Function(s)

Olfactory I Sensory Smell Identify odors

Optic II Sensory Vision Visual acuity,fields, color,nerve head

Oculomotor III Motor Upper lid elevation,extraocular eyemovement, pupil

constriction,accommodation

Physiologic "H"and near pointresponse

Trochlear IV Motor Superior obliquemuscle

Physiologic "H"

Trigeminal V Motor Muscles of mastication

Corneal reflex

Trigeminal V Sensory Scalp, conjunctiva,teeth

Clenchjaw/palpate,light touchcomparison

Abducens VI Motor Lateral rectus muscle Abduction,physiologic "H"


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Facial VII Motor Muscles of facial expression Smile, puff cheeks, wrinklef h d


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forehead, pryopen closed lids

Facial VII Sensory Taste-anterior two thirds of tongue

Vestibulocochlear VIII Sensory Hearing and balance Rinne test forhearing, Webertest for balance

Glossopharyngeal IX Motor Tongue and pharynx Gag reflex

Glossopharyngeal IX Sensory Taste-posterior one third oftongue

Vagus X Motor Pharynx, tongue, larynx,thoracic and abdominalviscera

Gag reflex

Vagus X Sensory Larynx, trachea, esophagus

Accessory XI Motor Sternomastoid and trapeziusmuscles

Shrug, head turnagainst

resistance


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Cranial Nerves and Its Examination

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