The Cranial Nerves

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12 pairs, (two are attached to the cerebrum and 10 are
attached to the brain stem
Nine are attached to the ventral surface of the brain
stem, while one is attached to the back of the midbrain
(Trochlear).
They leave the cranial cavity by passing through small
foramina in the skull bones
Both ‘names’ and ‘numbers’ are used to identify them
Their names indicate either their distribution or their
function
Their numbers (ROMAN numerals) indicate the order
in which the nerves arise from the brain.
Cranial Nerves
Like all nerves, cranial nerves are made up of
bundles of axons
Cranial nerves may be sensory, or motor, or mixed,
and may contain somatic and/or autonomic fibers.
•The olfactory system is closely associated functionally and
structurally with the limbic system.
• The nuclei of the last 10 cranial nerves are arranged in 7
columns in each side of the middle line in the brain stem.
•In the brain stem, in each side of the middle line, there are
medial 3 column contain motor nuclei and the lateral 4
column contain sensory nuclei.
I
Olfactory
II
Optic
III
Occulomotor
IV
V
Facial
VII Vestibulocochlear
I
(Statoacoustic)
IX
Glossopharyngeal
Trochlear
X
Vagus
Trigeminal
XI
Accessory
• Cranial part
• Spinal part
Abducent
XII
Hypoglossal
V1: Ophthalmic
V2: Maxillary
V3: Mandibular
VI
VII
Foramina of Exit
NERVE
FORAMEN
NERVE
FORAMEN
1st
Cribriform plate
of ethmoid
Optic canal
7th
Internal acoustic meatus,
2nd
3rd
4th
5th(V1)
8th
stylomastoid foramen
Internal acoustic
meatus
9th
Superior orbital
fissure
10th
6th
5th(V2) Foramen rotundum
11th
5th(V3)
12th
Foramen ovale
Jugular foramen
Hypoglossal canal
Ventral surface of brainstem
showing
attachment of the cranial nerves
Trochlear nerve s the only nerve that rise
from the
dorsal surface of the midbrain
Olfactory
Optic
Occulomotor
Trigeminal
Trochlear
Abducent
Glossopharyngeal
Facial & Vestibulocochlear
Vagus
Accessory
Hypoglossal
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General Somatic Afferent (GSA): Carries
information from skin, muscles, ligament and
joints
General Somatic Efferent (GSE): Activate skeletal
muscles
General Visceral Afferent (GVA): Carries sensory
information from visceral organs
General Visceral Efferent (GVE): Activate visceral
(smooth) muscles and glands
All the spinal nerves carry all the four components
General somatic afferent (GSA)
 General somatic efferent (GSE)
 General visceral afferent (GVA)
 General visceral efferent (GVE)
NB. All the spinal nerves carry all the
four components
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Four like the spinal nerves (GSA, GSE, GVA, GVE)
Three additional:
1-Special Somatic Afferents (SSA):
Mediate special sensations of vision and hearing &
equilibrium (2&8)
 2-Special Visceral Afferents (SVA):
 Mediate visceral sensation of taste & olfaction
 3- Special Visceral Efferent (SVE):
 Activate muscles of face, palate, mouth, pharynx and
larynx (derivatives of branchial arches)
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Not all the cranial nerves carry all the components
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Four like the spinal nerves
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General somatic afferent (GSA)
General somatic efferent (GSE)
General visceral afferent (GVA)
General visceral efferent (GVE)
Three additional: (for special senses &
pharyngeal arch muscles)
 Special somatic afferents (SSA): vision & hearing
 Special visceral afferents (SVA): taste & olfaction
 Special visceral efferent (SVE): supplying muscles
derived from pharyngeal arches
NB. Not all the cranial nerves carry all the
components
Type
Distribution
Efferent
General Somatic Efferent (GSE)
Skeletal muscles from Somites
General Visceral Efferent (GVE)
-Autonomic efferent
Smooth muscles and glands
Special Visceral efferent (SVE)
Skeletal muscles from pharyngeal
arches
Afferent
General Somatic Afferent (GSA)
Skin, skeletal muscles, joints and
bone
General Visceral Afferent (GVA)
–Autonomic afferent
Visceral organs
Special Somatic Afferent (SSA)
Retina, auditory and vestibular
organs
Special Visceral afferent (SVA)
Gustatory and olfactory receptors
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I-General Somatic Efferent
(GSE), column:
Motor nuclei which are in line
with the anterior horn cells of
the spinal cord.
It give rise to motor fibers
which supply striated muscles
developed from the myotomes.
(3,4,6 &12), (eye & tongue).
These are:
1- Hypoglossal nucleus in the
medulla oblongata.
2- Abducent nucleus in the
caudal Pons.
3- Oculomotor and Trochlear
nuclei in the midbrain.
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II- General Visceral
Efferent (GVE), column:
motor nuclei which give
parasympathetic fibers to
supply smooth muscles of
the organs, blood vessels
and glands.(3,7,9 &10)
It is homologues to the
lateral horn cells in the
spinal cord.
These are:
1- Dorsal motor nucleus of
vagus
2- Inferior salivatory nucleus.
3- Superior salivatory nucleus.
4- Edinger-Westphal nucleus.
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III- Special Visceral Efferent
(SVE) Column:
Motor nuclei which supply
muscles developed from the
pharyngeal arches,
(Branchiomotor cell column).
These are  (5,7,9 &10)
1-Ambiguus nucleus, in
medulla (9, 10 & cranial part of
accessory nerve)
2-Motor nucleus of the
trigeminal nerve, in the mid
Pons
3-Motor nucleus of the facial,
nerve in the caudal Pons.
I- General Visceral Afferent
(GVA) column:
Sensory nucleus which
receive,
visceral afferent from
pharynx, larynx, esophagus
,thoracic and abdominal
viscera:
Nucleus solitarius.
----------------------------------------II- Special Visceral Afferent
( SVA) column:
Sensory nucleus which
receives taste sensation:
Nucleus solitarius.
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III- General Somatic Afferent (GSA)
column: Sensory nuclei which
receive:
a)
General sensation: (PTPT) pain,
temperature, pressure and touch)
from the head): Trigeminal
sensory nucleus (Spinal and main
sensory nuclei of trigeminal
nerve.
b)
Deep (proprioceptive) sensation
from muscles of mastication and
tendons & ligaments of TMJ:
Mesencephalic nucleus of the
trigeminal nerve
----------------------------------------IV- Special Somatic Afferent (SSA)
column:
It receive special sensation from the
ear, Vestibulocochlear nuclei.
Brain
stem
Medulla
oblon
gata
Motor Column Nuclei
G.S.E.
Hypoglossal
Nucleus
XII
G.V.E.
parasympa
thetic
Dorsal
motor
nucleus
of Vagus
S.V.E.
Pharyngeal
arches
Nucleus
Ambiguus
Sensory Column Nuclei
G.V.A.
Solitary
Nucleus
S.V.A.
Abducent
Nucleus
Superior
salivary
nucleus
VI
Midbrain
Oculomotor
& Trochlear
Nuclei
III & IV.
EdingerWestphal
Nucleus
S.S.A.
Medial, Lateral &
inferior vestibular
nuclei
Dorsal & ventral
cochlear nuclei
Solitary
Nucleus
Inferior
Salivary
Nucleus
Pons
G.S.A.
Spinal nucleus
of trigeminal
nerve
Motor nuclei
of
trigeminal
&
facial
nerves
Solitary
Nucleus
Spinal nucleus
&
Main sensory &
Mesencephalic
nuclei of
trigeminal nerve
Mesencephalic
nucleus of
trigeminal nerve
Superior
vestibular
nucleus
Three Neurons:
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First order neuron:
From receptors to sensory nucleus.
(The cell bodies lie in the sensory ganglia)
Second order neurons:
From sensory nucleus to the contralateral
thalamus
Third order neurons:
From thalamus to cerebral cortex
Two neurons
 Upper motor neuron:
 From cerebral cortex to the motor
nucleus, mostly bilateral projection
except part of 7th and 12th nerves
 Lower motor neurons:
 From the motor nucleus to the
muscles
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Type:
Special sensory
Function:
Smell
Lesion :
Leads to loss of
sense of smell,
called anosmia
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Type:
Special sensory
Function:
Vision
Lesion:
Leads to visual
field defects and
loss of visual
acuity.
A defect of vision
is called anopsia
Type:
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Motor & Parasympathetic
 1- Oculomotor Nucleus
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lies close to the apex of the
periaqueductal grey mater of
the midbrain.
 It lies at the level of the
superior colliculus.
 Its efferent fibers run in the 3rd
CN to LPS and all extraocular
muscles except LR6 & SO4.
 It emerges in the
interpedunclar fossa medial to
the crus cerebri.
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2-Edinger-Westphal Nucleus,
lies close to the oculomotor
nucleus.
Gives preganglionic fibers to the
ciliary ganglion.
Many of the preganglionic fibers
traverse the Red Nucleus
Postganglionic fibers run in the
short ciliary nerve.
It supply the constrictor pupillae
and ciliary muscles.
Function:
Elevation of the upper eyelid,
Movements of eyeball,
Constriction of pupil and
Accommodation for near vision
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Lesion results in:
 Lateral squint
 Ptosis
 Diplopia
 Pupillary dilatation
 Loss of
accommodation
 Impaired downward
& outward
movement of the eye
ball on the damaged
side.
Trochlear nucleus
Lies in the periaqueductal
grey of the midbrain at the
level of the inferior
colliculus.
Axons pass dorsally and
cross the midline.
It courses around crus
cerebri between posterior
cerebral and superior
cerebellar arteries.
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It runs in the lateral
wall of the cavernous
sinus then to SOF.
It supplies SO4
It moves the eye
downwards and
medially.
Lesion:
diplopia, & difficulty in
walking downstairs
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Type:
Mixed
Three divisions:
 V1:Ophthalmic (sensory)
 V2:Maxillary (sensory)
 V3: Mandibular (mixed)
Function:
 Sensory:
 Carries general
sensations (pain, touch,
temperature, pressure,
vibration) from the face
& ant. scalp, orbit, nasal
and oral cavity, &
anterior 2/3 of tongue
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One large sensory ganglion
located in the middle cranial
fossa, at the apex of petrous
temporal bone, its central
process go to:
 Trigeminal Sensory
Nucleus.
It extends all through the
brain stem & upper cervical
segments
It is formed of 3 subdivisions:
1- Chief or Main or principal
sensory nucleus:
Lies in pontine tegmentum
close to the entry of 5th CN.
It receives touch and
pressure.
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2-Spinal nucleus &
tract of the trigeminal
nerve;
Extends caudally in the
medulla and upper
cervical segments.
It is continuous below
the with substantia
gelatinosa of Rolando.
It receives pain &
temperature sensations.
From the face, scalp,
orbit, nasal and oral
cavities, and anterior 2/3
of the tongue
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3- Mesencephalic
Nucleus: extends
rostrally into the
midbrain.
It carries proprioceptive
afferent fibers from the
muscles of mastication
and from the TMJ.
The cell bodies of all
sensations are present in
the trigeminal ganglion,
Except proprioceptive
sensation which lies in
the CNS.
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Axons arising from the
trigeminal nucleus decussate
to form the contralateral
trigeminal tract, or lemniscus
(2nd order neuron)
This terminates in the
contralateral PMVN of
thalamus, then to parietal
sensory cortex.
The trigeminal nucleus sends
fibers to the cerebellum from
which, the cerebellum send
fibers to the facial nucleus
which mediate facial
grimacing and eye closure
(corneal reflex).
Motor nucleus of
trigeminal nerve
It lies in pontine
tegmentum medial to
the main sensory
nucleus.
Fibers runs in the motor
root of the trigeminal,
then they join the
mandibular nerve.
It supply 8 (4+4)
muscles which
developed from the 1st
pharyngeal arch.
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
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Lesion:
Loss of general
sensations in the area
of distribution,
Paralysis of the
muscles of mastication
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Compression, inflammation or degeneration of
the 5th cranial nerve may result in a condition
called trigeminal neuralgia or tic douloureux.
This condition is characterized by recurring
episodes of intense stabbing , excoriating pain
radiating from the angle of the jaw along a
branch of trigeminal nerve.
Usually involves maxillary & mandibular
nerves, rarely in the ophthalmic division
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Type:
Motor
Supplies: Lateral rectus.
Function: moves the eye
laterally
Lesion:
Medial squint, diplopia,
loss of movement of the
eye laterally beyond the
midpoint.
Abducent Nucleus
Lies in caudal Pons
beneath the floor of the
4th ventricle.
Fibres pass ventrally and
emerge from the Pontomedullary junction
between the pyramid
and the Pons.
Abducent nerve passes
in the lateral wall of the
cavernous sinus then
through the SOF to
supply the lateral rectus
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Type:
Motor, special sensory,
parasympathetic
Function:
Motor to muscles of facial
expression (2nd pharyngeal
arch, lacrimal gland, nasal
and oral mucous membrane
submandibular & sublingual
salivary glands, taste fibers
from the anterior 2/3 of the
tongue
Lesion:
Bell’s palsy, loss of taste
from anterior 2/3 of tongue,
loss of Lacrimation and
salivation
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It joins the brain stem in the
cerebellopontine angle.
It consists of two roots:
1- Lateral root (nervous
intermedius), contains sensory
& parasympathetic fibers.
2- Medial root contains motor
fibers
Sensory fibers, carry taste
from the anterior 2/3rd of
tongue, floor of mouth and
palate, which end solitary
nucleus.
It also carry cutaneous
sensation from part of external
ear, which end in the spinal
nucleus of 5th CN
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Motor nucleus of facial
nerve
It lies in the caudal Pons.
The axons pass dorsally,
looping around abducens
nucleus beneath the floor of
4th ventricle.
Axons pass in the motor root
7th CN
N.B. Corticobulbar fibers
project bilaterally to the
upper part of the motor 7th
nucleus, and project to the
lower part of the nucleus
from the opposite side only.
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Damage to facial nerve results
in paralysis of facial muscles:
Facial (Bell’s palsy);lower
motor neuron lesion (whole
face affected)
NB. In upper motor neuron
lesion (upper face is intact) .
Face is distorted: drooping of
lower eyelid, sagging of the
angle of the mouth, dribbling
of saliva, loss of facial
expressions, loss of chewing,
blowing, sucking, unable to
show teeth or close the eye on
affected side
Superior salivatory
nucleus.
Lies in the Pons.
Axons run in the nervous
intermedius, to the
parasympathetic ganglia:
1- Submandibular
ganglion:
Postganglionic fibers pass
to submandibular &
sublingual salivary gland.
2- Pterygopalatine
ganglion: Postganglionic
fibers pass to Lacrimal
gland, nasal and oral
mucous membrane.
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Type:
Special sensory
Function:
 Vestibular part:
conveys impulses
associated with
balance of body
 Cochlear part:
conveys impulses
associated with
hearing
Lesion: loss of
hearing, tinnitus,
vertigo, dizziness,
ataxia and nystagmus
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Type: Motor, Sensory
(general & special)
parasympathetic
Function: motor to
(Stylopharyngeus), &
parotid gland,
carries taste fibers from
posterior 1/3 of tongue,
general sensations from
pharynx & palate.
Lesion:
Dysphagia (difficult
swallowing), loss of
sensation from throat,
loss of parotid secretion
and loss of taste from
posterior 1/3 of the tongue
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Type:
Motor (+cranial part of
accessory nerve),
Sensory (general &
special),
Parasympathetic
Function:
supplies visceral
muscles, glands of GIT,
muscles of the larynx
and pharynx, taste buds
on the base of tongue,
sensations from the
viscera Carotid sinus and
carotid body

Lesion Leads to:
 Loss of gag reflex
 Difficulty in swallowing
 Loss of sensations from
the abdominal viscera
 Loss of taste from the
base of tongue &
epiglottis
 Hoarseness or loss of
voice
 Gastrointestinal
dysfunction
 Blood pressure
anomalies (with CN IX),
fatal if both are cut
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Type:
Motor,
It has two parts:
cranial & spinal
Function:
 Cranial part: unites
with the vagus and
supplies voluntary
muscles of larynx,
pharynx and esophagus


Spinal part: supplies
(sternomastoid &
Trapezius)
Lesion: Difficulty in
swallowing, and speech.
Inability to turn the head,
and raise the shoulder.
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Type:
Motor
Function:
Motor to all muscles of
the tongue except
palatoglossus. Allows
movements of tongue
during speech and
swallowing
Lesion: difficulty in
chewing and speech.
The tongue paralyses,
atrophies, becomes
shrunken and furrowed
on the affected side, and
on protrusion it deviates
to the affected side
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Causes:
Severe head injuries, skull bone
fractures or penetrating wounds
Brain lesions
Compression due to raised intracranial
pressure (due to any space occupying
lesion e.g. tumor, hematoma, or CSF
obstruction )
Cavernous sinus thrombosis

Compression of
abducent nerve
and internal
carotid artery

The integrity of nerves is assessed
by examining the:
 The sensations in the area of
distribution
 Action of muscles
 Integrity of reflexes
 Secretory activity of glands
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Pupillary (light) CN 2, 3
Accommodation CN 2, 3
Corneal (Blinking) CN 5,7
Lacrimation 5, 7 (stimulus may be visual or even
thought or emotions)
Salivation CN 1, 2, 5, 7, 9 (stimulus may be
olfactory, visual, taste, or even thought of food)
Sneezing CN 1, 5, 9, 10, 11, phrenic, intercostals
Vomiting CN 1, 5, 7, 9 (stimulus may be olfactory,
visual, taste, or even thought)
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Yawning CN 5, 7, phrenic, intercostal
Swallowing CN 5, 7, 9, 10, 11, 12
Jaw jerk CN 5
Stapedial CN 8, 7
Cough CN 9, 10, 11, phrenic, intercostals
Gag CN 9, 10
Carotid sinus reflex CN 9, 10
Olfactory nerve:
Ask the patient to identify items with very
specific odors,(e.g.. coffee, alcohol,
perfume), placed under the nose.
Each nostril is tested separately
Optic nerve:
Ask the patient to read an eye chart.
 Peripheral vision is tested by detecting object or
movement from corners of the eyes
Occulomotor nerve:
Note the ability to move each eye upward, downward
and inward by asking the person to follow a target
moved by the examiner.
 Also examine the constriction of pupil &
accommodation
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Trochlear:
 Note the ability to move each eye downward and
inward
Trigeminal nerve:
 General sensations on face are tested by using a pin
and a wisp of cotton.
 Blink reflex is tested by touching the cornea of the
eye with a cotton wisp.
 Strength and action of muscles of mastication are
tested by asking the person to clench the teeth and
open the jaw against resistance
Abducent nerve:
 Note the ability to move each eye outward beyond
the midline
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Facial nerve:
 The action of muscles of face is tested by asking
the person to smile, to open the mouth, to show
the teeth, and to close the eyes tightly.
 Taste sensations from anterior 2/3 tongue is
tested using substances that are sweet, sour,
salty and bitter
Vestibulocochlear nerve:
 Hearing is tested with a tuning fork.
 Balance is tested by asking the person to walk
on a straight line.
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
Glossopharyngeal & Vagus nerves:
(cranial part of Accessory nerve) :
 The person is asked to swallow.
 The person is asked to say ‘ah-h-h’ to check
the movements of palate and uvula.
 The ‘gag reflex’ is tested by touching the back
of the throat by the tongue depressor.
 The person is asked to speak to check the voice
for hoarsness.
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Spinal part of Accessory nerve:
 The person is asked to turn the head
and to shrug the shoulders against
resistance provided by the examiner
Hypoglossal nerve:
 The person is asked to stick out the
tongue, to observe the deviation to
one side or the other
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