Cranial Nerves Top

8/7/2019 Cranial Nerves Top

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Cranial nervesCranial nerves



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1st Olfactory.

2nd Optic.

3rd Oculomotor.

4th Trochlear.

5th Trigeminal.

6th Abducent

7th Facial.

8th Acoustic.

9th Glossopharyngeal

10th Vagus.

11th Accessory

12th Hypoglossal




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We will discuss:

1. The central course of each nerve2. The clinical consequences of

damage to the components of the

nerve




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�GSA ± General Somatic Afferent

Convey sensory input from skin, muscle, bone and joints to the CNS

�GVA ± General visceral Afferent

Convey sensory input from visceral organs to the CNS

�GSE - General Somatic EfferentConvey motor output to skeletal muscles

�GVE - General Visceral Efferent

Convey motor output to glands, and smooth muscles

�SVA - Special Visceral Afferent

Convey sensory input of a special sense (e.g. taste, olfaction)

�SSA - Special Somatic Afferent

Convey sensory input of hearing, balance and vision

SVE - Special Visceral Efferent

Convey motor output to a special organ

Functional componentsFunctional components



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The somatic motor (efferent) Cranial nervesThe somatic motor (efferent) Cranial nerves

The Visceral motor (efferent) Cranial nervesThe Visceral motor (efferent) Cranial nerves

The sensory (afferent) cranial nervesThe sensory (afferent) cranial nerves



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The somatic motor (efferent) Cranial nervesThe somatic motor (efferent) Cranial nerves

Cortex ± 1st order neurons

Internuncial neurons -2nd order neurons

Lower motor neurons ± 3rd order neurons

corticonuclear (bulbar)

fibers



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�All nuclei are bilaterally

innervated except for :

�Part of facial nucleus

that innervates themuscles of the lower

part of the face

�Part of hypoglossal

nucleus that innervates

the genoiglossus

muscle

The Somatic motor (efferent) Cranial nervesThe Somatic motor (efferent) Cranial nerves



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� Cranial Outflow Of The

Parasympathetic Part Of

Autonomic System

The Visceral motor (efferent) Cranial nervesThe Visceral motor (efferent) Cranial nerves

NucleusCranial Nerve

Edinger Westphal3

Superior Salivatory7

Lacrimal7

Inferior salivatory9

Dorsal Motor 10



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�Arise from groups of

nerve cells outside

the brain

�These nerve cells

may be grouped to

form ganglia



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From organs ± 1st order neurons

Nucleus to thalamus -2nd order neurons

Thalamus to cortex ± 3rd order neurons



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Categorization Of Cranial Nerves

By A/Efferent Components

CN 1,2,8Pure sensory

CN 3,4,6,11,12Pure motor

CN 5,7,9,10mixed



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Cranial Nerve ICranial Nerve I -- Olfactory NerveOlfactory Nerve

� The olfactory system consists of the olfactory epithelium,

bulbs and tracts along with olfactory areas of the brain

collectively known as the rhinencephalon.

� The olfactory nerve has only a special sensory component

-olfaction.



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�The olfactory nerves are distributed to the mucous membrane of the

olfactory region of the nasal cavity

�Olfactory receptor cells initiate action potentials in response to

odorants



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processes of the receptor cells assemble into small bundles and

pass through the cribiform plate to synapse on secondary sensory

neurons in the olfactory bulb



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Ethmoid bone



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The olfactory bulbs:

�pair of small structures,

lying within the cranial

vault, immediately above

the cribriform plate�contain the cell bodies

of the secondary

sensory neurons,

arranged in five cell layer that surround a central

core of white matter.




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�This central corecontinues posteriorly

as the olfactory tract.

The olfactory tract

divides into the largelateral and thesmaller medial

olfactory




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lateral olfactory

striae to primary

olfactory cortex:p re p iform cortex & Amygdala

medial olfactory

striae project to thecontralateral

olfactory bulb by wayof the anteriorcommissure



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Through stria

medullaris thalami tothalamus in the

mediodorsal nucleus (MD).

To orbital gyri an

area essential for theconscious perception ofodors.



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��When damaged (e.g., ethmoid bone fracture),When damaged (e.g., ethmoid bone fracture),

results inresults in anosmiaanosmia, , loss of olfactory sensationloss of olfactory sensation or or

hyposmia

hyposmia

��More common but often temporaryMore common but often temporary -- physicalphysical

obstruction of the nasal passage due toobstruction of the nasal passage due to rhinitis or rhinitis or

sinusitissinusitis

��Impairment in olfaction may be a very early sign inImpairment in olfaction may be a very early sign in

the onset of Alzheimer¶s dis., Parkinson¶s dis,the onset of Alzheimer¶s dis., Parkinson¶s dis,

Cystic Fibrosis, tumors of frontal lobes or Cystic Fibrosis, tumors of frontal lobes or

meningiomasmeningiomas

Clinical correlationClinical correlation



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Cranial Nerve VCranial Nerve V -- Trigeminal NerveTrigeminal Nerve

General characteristics

� largest cranial nerve.

� 2 functional components:

� General somatic afferent (GSA,

somatosensory) - sensationfrom face, eye, nasal and oral

cavities.

� Special visceral efferent (SVE,

motor) - muscles of mastication

� The trigeminal n. also innervates

most of the dura mater.



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�Leaves the brain stem

through the middle

cerebellar peduncle .

�The major portion carries

the primary afferent fibers

�The minor portion carriesthe motor fibers



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T he trigeminal

ganglion

Within 1-2 cm swells toform the very largetrigeminal ganglion.

Contains the cell bodies

of the primary sensoryneurons



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As the fibers exit the trigeminal

ganglion they form 3 primary

divisions:

Ophthalmic ( V1) - sensory

- innervates the upper portion of the

face

Maxillary (V2)- sensory ±innervates the mid face region

Mandibular (V3) -sensory+motor ±

innervates the lower facial region





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1. Main sensory

2. Spinal

3. Mesencephalic

4. Motor

Nuclei



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Nuclei

S pinal trigeminal

nucleus

�In the medulla and

pons (C1-C3).

�Pain and

temperature input

�To Ventro Posterior

Medial nucleus of

thalamus



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Nuclei

M ain sensory nucleus

�In the pontine tegmentum

�Tactile input from the face

�Projects to VPM of

thalamus



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Nuclei

M esencephalic

nucleus

�Accompany the motor branches to the muscles of

mastication and extra

ocular muscles.

�End on muscle spindle and

proprioceptive receptors.

�Bypass ganglion



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Nuclei

M otor nucleus

�In pontine tegmentum

�Innervates muscles:

�mastication

�tensor tympani

�tensor veli palatini

�Mylohyoid

�ant. Belly of digastric



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Non or little overlapping!

Loss of general sensation fromthe face and mucous membranes

of the oral and nasal cavities

Paralysis of the muscles of

mastication


Clinical correlations-lesions of CN V



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Deviation of the

patient's jaw to the

affected side, dueto the unopposed

action of the

opposite lateral

pterygoid muscle





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Paralysis of the tensor tympani, leading to hyperacusis





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Loss of the corneal reflex

(afferent limb, CN V-I)

corneal reflex

1. The afferent limb is the

ophthalmic nerve

2. The efferent limb is the

facial nerve



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Herpes zoster

�A viral infection affecting the

divisions of the trigeminal

ganglion

�Results in considerable pain

and ulceration of the skin and

mucous membranes supplied

by the affected fibers.

�The ophthalmic division is

most frequently affected -

Her pes zost er opht halmicus



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Trigeminal neuralgia

�One of the most common

clinical problems. Usually

patient over 50 yrs

�Periods of severe pain

�Localized to one side of the

face. Involves area of innervation of one or more

divisions

�Usually the maxillary or

mandibullar divisions



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Trigeminal neuralgia

�Usualliy no motor or

sensory deficit on

examination

�In the young patient

consider MS, in the older

consider basilar artery

aneurism or tumor of the

cerebellopontine angle

�However, mostly idiopathic



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� Has 2 parts: the facial

nerve proper and the

intermediate nerve

� Both exit together the

brainstem in the

cerebellopontine angle.

� Enters the internal

auditory meatus and

facial canal.

Cranial Nerve VIICranial Nerve VII -- Facial NerveFacial Nerve




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� The facial nerve is the motor nerve to

the muscles of facial expression

� The intermediate nerve contains 3

sensory components:

1. Taste

2. salivation

3. sensory- auricle and ext. auditory

meatus



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1. Main motor in reticularformation in pons

2. Parasympathetic:

a. lacrimal. Recieves from

hypothalamus & trigeminal

b. Superior salivatory.Recieves from hypothalamus

3. Sensory (solitary)

Nuclei




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Greater petrosal nerveFacial nerve

Chorda tympani

solitary

nucleus

GVA ±

sensory-

nasal cavity,sinuses, softpalateSVE - Motor

to stapediusmuscle

Facial nucleus

SVE - Motor to facialexpression muscles

spinal

nucleusof V

GSA ± sensory-auricle and ext.auditory meatus

Superior

salivatory

nucleus &

lacrimalnuclei

GVE ±

parasympath

etic ± salivary

glands

GVE ±

parasympathetic ± nasal oral

and palatineglands,lacrimal gland

Geniculate ganglionPterygopalatine

ganglion

Submandibular ganglion

Brain stem SVA -Taste from

ant 2/3 of tongue



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Results in flaccid paralysis of the muscles of facial

expression


Clinical correlations-lesions of CN VII ± motor portion



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Bell's palsy

is caused by trauma to the nerve

beyond the nerve¶s exit from the

skull

is a lower motor neuron (LMN)lesion with paralysis of all

muscles of facial expression.




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Central facial palsy

(supranuclear palsy)

�results from transaction of

corticobulbar fibers in the

internal capsule.

�is an upper motor neuron

(UMN) lesion affecting the

muscles of the lower face.

�results in contralateral facial

weakness below the orbit,

sparing the of the upper

muscles of facial expression





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Result in the following conditions:

1. Loss of the corneal (blink) reflex (efferent limb), which may lead to corneal

ulceration

2. Loss of taste from the anterior two-thirds of the tongue

3. Diminished salivation

4. Hyperacusis (increased auditory sensitivity), due to stapedius paralysis

5. Loss of tearing


Clinical correlations-lesions of CN VII



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Glossopharyngeal Nerve (CN IX)Glossopharyngeal Nerve (CN IX)

�Exits the brainstem (medulla)

from the postolivary sulcus with

CN X and CNXI.

�Exits the skull via the jugular

foramen with CN X and CN XI



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1. Main motor

2. Parasympathetic

3. Sensory (solitary)

Nuclei




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Main motor

1. in reticular formation in

medulla oblongata.Formed by sup. End ofnucleus ambiguus.

2. Recives corticonuclearfibers bilaterally.

3. Innervates

stylopharengeus muscle

Nuclei




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Parasympathetic (inf. Salivatory).

1. Afferent fibers from

hypothalamus.

2. Recives corticonuclearfibers bilaterally and

olfactory input throughtreticular formation.

3. Innervates parotid

gland.

Nuclei




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Sensory



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Brain stem

Lesser petrosal nerve

GVE ±

parasympathetic ±

parotid gland

inferior

salivatory

nucleus

Otic ganglion

Tympanicnerve

superior ganglion

spinal

nucleusof V

GSA ± sensory-auricle and ext.auditory meatus± pain, temp,

touch

Nucleus

ambiguus

SVE ± motor -Stylophryngeous muscle

inferior ganglion

solitary

nucleus

SVA, ± Taste frompost 1/3 of tongueand

GVA ± sensory ±

pharyngealmucosa andtongue

GVA ±

sensory ±

carotid sinus±

baro/chemoreceptors

Glossopharyngeal nerve



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Result in the following conditions:

I. Loss of the gag (pharyngeal) reflex

(interruption of afferent limb)

II. Loss of taste from the posterior third of the

tongue

Clinical correlations-lesions of CN IX



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Cranial Nerve XICranial Nerve XI-- Accessory NerveAccessory Nerve

� A motor nerve with its neurons

of origin in the upper cervical

segments of the spinal cord

(SVE)

� Mediates head and shoulder

movement and innervates

laryngeal muscles.




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Medulla

Foramen magnum

Jugular Foramen

Spinal

accessory

nucleus

spinal division

SVE Innervates the

sternocleidomastoid(with C2) andtrapezius muscles(with C3 and C4).

Spinal cord CI-C6

Nucleus

ambiguus

Aberrant vagal fibers

Vagus nerve

Vagus nerve

Cranial division



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Clinical correlations

Damage to the spinal accessory

nerve:

�Uncommon

�Flaccid paralysis or paresis of the

muscles and subsequent atrophy

�Paralysis of the sternocleidomastoid

muscle results in difficulty in turning

the head to the side opposite to the

lesion.

� Paralysis of the trapezius muscle

results in a shoulder drop and in the

inability to raise the ipsilateral

shoulder .



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Cranial Nerve XIICranial Nerve XII-- Hypoglossal NerveHypoglossal Nerve

�Mediates tongue movement.

�Is a pure GSE nerve.

�Arises from the hypoglossalnucleus of the medulla.

�Innervates intrinsic and

extrinsic muscles of the

tongue.




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�Exits the medulla in the preolivary

sulcus.




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When transected

�hemiparalysis of the tongue

results.

�When protruded, the tongue

points toward the weak sidedue to the unopposed action

of the opposite genioglossus

muscle.

Clinical correlations

Cranial Nerves Top

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