Cranial Nerves & Nuclei: Anatomy and Functions

Cranial nerves & Cranial nerve nuclei
:
The base of the brain showing
locations of cranial nerves
There are 12, paired cranial
nerves.
The first 2 cranial Ns. attach
directly to forebrain (frontal lobe) , while
the rest attach to brain stem.
Olfactory system is attached to
forebrain and is referred to as the limbic
system, / optic N. also is discribed in
visual pathway.
Cranial Ns. from 3 - 12 have
nuclei (cranial N.nucluei) in the
brain stem , receiving afferents Fs. Or
send efferent Fs. as the cranial Ns.

Superficial attachements of Cranial
nerves :
The base of the brain
showing locations of cranial
nerves
Occulomotor & trochlear Ns.
are attached to midbrain.
Trigeminal N. is attached to
antero-lateral surface of pons.
Abducent, Facial & vestibulo-
cochlear Ns. are lying between
pons & M.O. from medial to lateral.
Hypoglossal N. is attached to
antero-lateral sulcus of M.O. / but
glossopharyngeal, vagus &
accessory Ns. are attached to
postero-lateral sulcus of M.O.

Dorsal aspect of brain stem showing
locations of Afferent cranial N. nuclei
(left) , and Efferent cranial N.nuclei
(right) , in which the same colours
have a common embryological origin.
Afferent Nerve Nuclei :
Fibres carrying general sensation
from the head via trigeminal N.
terminate in a large trigeminal
sensory nucleus that extends the
whole length of brain stem and
cervical spinal cord.
Fibres carrying hearing &
motion/ positional sense via
vestibulo-cochlear N. terminate in
cochlear & vestibular nuclei that are
located in upper M.O.
Visceral afferents carrying taste
sensation via facial & glossopharyngeal
Ns., terminate in nucleus solitarius
located in upper M.O.

Efferent Nerve Nuclei :
Somatic efferent column : supplies
striated Ms. in head, including : yellow colour
1- Oculomotor nucleus.2-Trochlear nucleus.
3-Abducent nucleus. 4-Hypoglssal nucleus.
Branchiomotor (special visceral)
efferent column : supplies striated Ms. derived
from branchial arches, including : orange
1- Trigeminal motor nucleus.
2- Facial motor nucleus.
3- Nucleus ambiguus.
Parasympathetic (general visceral)
efferent column : supplies glands & smooth
Ms. of viscera , including : pink colour
1- Edinger- Westphal nucleus.
2- Sup.& Inf. Salivary nuclei.
3- Dorsal nucleus of vagus.

Somatic efferent Nerve Nuclei
Oculomotor nucleus : lies at the
base of periaqueductal grey of
midbrain at the level of superior
colliculus. Its efferent Fs. run in
oculomotor N. to innervate levator
palpebrae superiooris + all
extraocular Ms. Except L.R & S.O
 Trochlear nucleus : lies at the
ventral part of periaqueductal grey of
midbrain at the level of inferior
colliculus. Its efferent Fs. run in
trochlear N. to innervate S.O.muscle.

Oculomotor & trochlear Nerves
Anterior view of midbrain
Oculomotor nerve : emerges from
the medial aspect of each cerebral
peduncle e.g. through the
interpeduncular fossa.
Trochlear nerve : emerges from
back of midbrain, caudal to inferior
colliculus and then passes laterally
around cerebral peduncle to appear
on the anterior view of midbrain.
Posterior view of midbrain

Somatic efferent Nerve Nuclei :
Abducent nucleus : lies in the
caudal pons , beneath floor of
4th vent. Its efferent Fs. run in
abducent N. to supply L.R.
Hypoglossal nucleus : lies in
the rostral M.O. its efferent Fs.
run in hypoglossal N. to supply
all Ms. of tongue Except
palatoglossus muscle.

Branchiomotor efferent Nerve Nuclei
Trigeminal motor nucleus : lies
in the tegmentum of the mid-pons and its motor
Fs. run in mandibular branch of trigeminal N.
to supply structures of 1st pharyngeal arch as
Ms. of mustication, mylohyoid, ant.belly of
digastric, tensor tympani (middle ear) & tensor
veli palatini.(soft palate).
Facial motor nucleus : lies in the
caudal pontine tegmentum, its motor Fs. run in
facial N. to innervate Ms. of facial expression,
stapedius muscle (middle ear) & other
Ms.derived from 2nd pharygeal arch
(stylohyoid,post.belly of digastric).
Nucleus ambiguus : it is a long nucleus
lies in M.O., sending motor Fs. in 9th ,10th &
cranial root of 11th nerves to innervate Ms. of
pharynx & larynx derived from 3,4& 6

Parasympathetic efferent Nerve
Nuclei : Edinger-Westphal nucleus
lies in midbrain adjacent to oculomotor
nucleus. It is the parasymp. part of
oculomotor nucleus. It gives preganglionic
parasymp. motor Fs. Via oculomotor N. into
ciliary ganglion, which sends postganglionic
Fs. to innervate sphincter pupillae & ciliary
Ms. in the eye.
Superior salivary nucleus :
lies in pontine tegmentum, it gives
preganglionic Fs. Via facial N. into pterygo-
palatine & submandibular ganglia , which
gives postganglionic Fs. to innervate lacrimal
gl., Nasal and oral M.Ms. & submandibular
and sublingual salivary glands…. respictevly

Parasympathetic efferent Nerve
Nuclei : Inferior salivary nucleus :
lies in pontine tegmentum, sends pre-
ganglionic Fs. Via glosso-pharyngeal
N. into otic ganglion , which sends
post-ganglionic Fs. to parotid gland.
Dorsal motor nucleus of
vagus : lies in the rostral M.O.
lateral to hypoglossal nucleus, it gives
preganglionic parasymp.Fs. Via
vagus N. to innervate thoracic &
abdominal viscera.

Cranial Nerves : III : Oculomotor N.
This N. contains 2-types of fibres : 1- Somatic motor efferent Fs.
from oculomotor nucleus to all extrinsic eye Ms. Except S.O &L.R.
2- Preganglionic parasymp. motor Fs. from Edinger-Westphal
nucleus to constrictor pupillae & ciliary muscle via postganglionic
Fs. of short ciliary nerves arise from ciliary ganglion.
This N. lying in the lateral wall of cavernus sinus before passes to
orbit through sup.orbital fissure.

Eye movements brought about by
the extraocular muscles :
Oculomotor nerve supplies sup.rectus, inf.rectus , medial rectus ,
inferior oblique & levator palpebrae superioris, so it elevates ,depresses
and adducts the eyeball.
Trochlear N. supplies S.O, it depresses eyeball down & medial
Abducent N. supplies L.R , it abdducts eyeball.

T.S of midbrain at the level of sup.colliculus
to illustrate the pathway of pupillary light reflex.
If the light is illuminated on one eye , it
causes constriction of the pupil of the same
eye due to contraction of constrictor
pupillae muscle…. This is called
direct light reflex.
The constriction of the pupil of the non-
illuminated eye is called
consensual (indirect) light reflex.
During the visual pathway ,small Fs. leave
the optic tract to synape in the pretectal
nucleus, which projects bilaterally Fs. to
Edinger-Westphal nuclei of
occulomotor ,that send efferent
parasympathetic Fs. Via oculomotor nerves
on both sides to sphincter pupillae ms.
Note that pretectal area involves in
mediation of pupillary light reflex.

Accomodation Reflex :
Fixation upon a nearby object,
involves contraction of ciliary
muscles to increase the convexity
of lens, thus focusing the image.
It is also accompanied by
pupillary constriction due to
activation of constrictor pupillae m.
Also, Cortico-bulbar Fs.( visual
frontal cortex) activate the
parasymp. Edinger-Westphal nuclei
on both sides to supply ciliary &
sphincter pupillae Ms.
Optic pathway and Visual reflexes
(pupillary light R.+ accomodation R.)

IV : Trochlear Nerve :
T.S of midbrain at the level of
inferior colliculus ,showing the
location of trochlear nucleus (at the
base of periaquaductal grey matter) and
course of trochlear N.Fs.
This N. carries only somatic
motor efferent Fs. from the trochlear
nucleus in midbrain (level of inferior
colliculus) to supply the S.O. of
opposite side.
Trchlear N. ,the only nerve
emerges from the post.surface of
brain - stem ,then appears on the
ventral aspect of the midbrain.
It runs in lateral wall of cavernus
sinus and enter the orbit through
sup. orbital fissure to supply S.O.

VI : Abducens Nerve :
Like trochlear N., contains only
somatic motor neurones in the
abducens nucleus ,which located in
caudal pons beneath the floor of 4th
ventricle.
Fibres emerge from the ventral
surface of brain stem at the junction
between the pons & pyramid of
M.O
The nerve then passes in the
cavernous sinus and enter orbit
through sup. orbital fissure to supply
L.R muscle to abduct the eyeball.

Lesions of cranial nerves III,IV and VI :
Oculomotor N. palsy by a lesion
of occulomotor nucleus in mibrain or
compression by aneurysm or tumour
leads to ptosis , dilatation of pupil that
is unresponsive to light &
accommodation reflexes and inability to
move eyeball upwards, downwards and
inwards (adduction).
Abducens N. palsy leads to
inability to move the eyeball outwards
(abduction).
Combined unilateral palsies of III,
IV,and VI during their course in
cavernous sinus , sup. Orbital fissure or
within the orbit , lead to:
1-ptosis.
2-dilatation of pupil.
3-paralysis of all eye movements
Note right ptosis .
Note with elevation of eyelid, the eyeball can be
seen abducted and the pupil dilated.
Note failure of left eyeball abduction due to
lesion of left abducent N.

V : Trigeminal Nerve :
Superficial distribution of
sensory fibres of the 3 divisions
of trigeminal nerve.
It is the largest cranial N., it
has both sensory Fs. that are
distributed via ophthalmic,
maxillary and mandibular to the
head --- & motor Fs. to Ms.of
mastications (Ms.of 1st arch).
It attaches to the ventrolateral
aspect of pons by 2 roots
(a large sensory laterally & a
smaller motor medially).

V : Sensory components
of Trigeminal Nerve :
Brain stem and location of
trigeminal sensory nucleus &
its major connections.
Trigeminal sensory nucleus
consists of 3-subnuclei :
1-Chief (principle) sensory nucleus
lies in pontine tegmentum (mid-
pon), it recevies touch sensation.
2-Spinal nucleus extends caudally
through the medulla and upper
cervical spinal cord to become
continuous with substantia
gelatinosa, it recevies pain &
temp.sensation from face & scalp.
3-Mesencephalic nucleus in
midbrain, it recevies proprioception
(deep) sensation from head.

Sensory components of Trigeminal nerve
(for touch/pressure & pain/temperature) :
Afferent Fs. of touch, pressure, pain
& temperature are recevied from skin
of face ,scalp, via peripheral
processes
(ophthalmic,maxillary+sensory part
of mandibular)… whose cell bodies
(first neurones) are situated in
trigeminal ganglion, located at the
convergence of ophthalmic , maxillary
and mandibular nerves.
Afferent Fs.(centeral axons)
conveying touch terminate in principal
nucleus, and those carrying pain &
temp. end in nucleus of spinal tract
of trigeminal.

Sensory components of Trigeminal nerve
(for proprioceptive sensation):
1st neurone for Proprioceptive :
peripheral afferents (via mandibular nerve)
from Ms.of mustication & temporo-
mandibular joint have their cell bodies not in
trigeminal ganglion but in mesencephalic
nucleus of trigeminal ( the only primary
afferents to have cell bodies within C.N.S).
The centeral axons of the cells of
mesencephalic nucleus descend medially to
synapse around Motor Nucleus of Trigeminal
(2ND neurone) in pons.
Axons arising from 2nd neurones in
trigeminal nuclei (sensory &motor) decussate
to form contralateral trigemino-thalamic tract,
which terminates in contralateral (VP) nucleus
of thalamus that sends Fs. to sensory cortex.

Motor components of
Trigeminal Nerve :
The motor Fs.of trigeminal N.
arise from the trigeminal motor
nucleus , which lies in pontine
tegmentum.
The axons leave the pons to
join the mandibular division of
trigeminal , to innervate :
1- 4 Ms. of mastication.
2- 4 other Ms. : mylohyoid,
anterior belly of digastric, tensor
palati (soft palate) & tensor
tympani (middle ear).
T.S of pons at the level of
Trigeminal nuclei.

Lesions of Trigeminal Nerve :
 Herpes Zoster infection of sensory root of trigeminal
N. ….. Leads to severe stabbing pain & eruption of
vesicles localised to skin supplied by its branches :
ophthalmic , or maxillary or mandibular N…..
Trigeminal Neuralgia.
 Syringo-bulbia ,it is a disease of unknown etiology
which affects the closed M.O, causes central cavitation
of medulla caudal to 4th V. , leading to destruction &
damage of decussating trigemino-thalamic Fs., causing
selective loss of pain & temp. sensation in the face
( dissociated sensory loss), mostly leading to destruction
of the cervical spinal cord (syringomyelia) =cavitation of
spinal cord.

VII : Facial Nerve :
It carries 3-types of fibres : 1- Efferent motor (branchiomotor) Fs. From facial
motor nucleus in pons to : Ms. of 2nd arch , Ms.of facial expression & stapedius.
2-Afferent Taste sensory Fs. From anterior 2/3 of tongue. These Fs. are processes
of cells in sensory geniculate ganglion in middle ear , and run in nervus
intermedius to end in nucleus solitarius in M.O.
3-Efferent parasympathetic secretomotor Fs. Carried by lateral root of facial nerve
(nervus intermedius) From sup.salivary nucleus in pons : to pterygopalatine &
submandibular ganglia to lacrimal gland , palate, nasal & oral m.m, /and
submandibular & sublingual salivary glands.

The lateral root contains sensory & parasymp.Fs. is called nervus
intermedius , / but the medial root is the motor root.
The sensory Fs. ends in nucleus solitarius in medulla and then
Fs. project to V.P.nucleus of thalamus, which sends Fs. to sensory
cortex of parietal lobe.

Motor Fs. of facial nucleus in pons , via facial N. looping over
abducens nucleus , then leaving the brain stem to supply : Ms.of
facial expression ,platysma ,stylohyoid , post.belly of digastric &
stapedius of middle ear.
Facial motor nucleus receives other afferents from area of brain
stem for mediation of certain reflexes and also from cerebral cortex
, (cortico-bulbar pyramidal tract).

Reflex connections mediate 1- protective eye closure in response to sudden strong
stimuli through tectobulbar Fs. descending from sup. Colliculus (tectum of midbrain) to
end in facial motor nucleus, then, via facial N. to supply orbicularis oculi to close &
protect the eye. 2-
corneal reflex through Fs. from trigeminal sensory nucleus, to motor nucleus of facial,
then via facial N. to orbicularis oculi in response to tactile stimulation of cornea.
Afferents from cortical motor areas (cotico-bulbar Fs.) supply Ms. of upper face
which are distributed bilaterally (from Rt.& left C.hemispheres) , but those supplying
Ms. of lower face are crossed. So, Unilateral upper motor neurone lesion (UMNL)
leads to lower facial Ms. paralysis of opposite side only, but upper Ms. are intact.

Bell’s Palsy :LMN facial paralysis
 It is due to acute unilateral inflammation of facial
nerve within the skull (in facial canal).
 Manifested by paralysis of facial muscles of upper &
lower parts of face on the same side of lesion..
 Manifested by pain around ear , - failure to close eye,
absent corneal reflex, - loss of taste sensation in
anterior 2/3 of tongue, & hyperacusis =increased
sound perception due to paralysis of stapedius.
(action of stapedius = damping down the intensity of high
pitched sounds by damping down movement of stapes)
 If herpes zoster virus is the inflammatory agent ,
a vesicular rash appear in ext. auditory canal & m.m
of oropharynx (Ramsay Hunt syndrome).

VIII : Vestibulocochlear Nerve :
It is purely sensory nerve.
It has 2-components ,
1- Vestibular N., which carries
balance sensation from utricle,
sacule & semicercular canals.
2- Cochlear N., which carries
hearing sensation.
It emerges from ponto-medullary
junction at cerebello-pontine angle
with the facial N.

VIII : Vestibular Nerve :
Distribution of Vestibular Nerve
Cells of origin :
vestibular ganglion ,lying in
internal acoustic meatus.
The peripheral process :
carries sensation from
utricle,saccule & semicircular
canals (membranous labyrinth).
Central process : leaves
vestibular ganglion and joins
cochlear N.
They enter the brain in groove
between pons & M.O. to end in
the Vestibular nuclei in M.O.

Vestibular Nerve Fibres :
Vestibular nerve nuclei & their central
connections (rostral M.O.)
1-Efferent Fs. From the 4
vestibular nuclei to cerebellum
( flocculo-nodular lobe) through inferior
cerebellar peduncle to control body
balance (equilibrium).
2-Efferent Fs. descend uncrossed
to spinal cord from lateral vestibular
(Deiter’s)nucleus) to form vestibulo-
spinal tract , assist to maintain balance by
influencing muscle tone of body.
3-Efferent Fs. Also pass to ocular
nuclei of oculomotor , trochlear &
abducent through medial longitudinal
fasciculus , for coordination of head &
eye movements.

Vestibular Nerve Fibres :
Vestibular nerve nuclei & their
central connections
4-Efferent Fs. ascend from
vestibular nuclei to relay in (VP)
nucleus of thalamus to reach
the cerebral cortex , at the
vestibular area of sensory cortex
which is uncertain but is
probably adjacent to primary
sensory cortex area in parietal
lobe at inferior parietal lobule
just above lateral fissure or
adjacent to auditory cortex in
temporal lobe.

Lateral aspect of cerebral
hemisphere
location of vestibular area in cerebral cortex : probably adjacent to the
sensory cortex in parietal lobe/ or adjacent to auditory cortex in temporal
lobe.

Ascending connections of auditory
component of vestibulo-cochlear nerve.
 Cochlear Nerve :
1st order neurones conduct
impulses of sound from the
organ of Corti in the cochlea.
Fs. of cochlear N. are the
central processes of nerve cells
located in spiral ganglion.
The Fs. bifurcate to end in
dorsal & venteral cochlear nuclei
, which lie close to inf.cerebellar
peduncle.

At trapezoid body some
Fs.may terminate in superior
olivary nucleus.
Most Fs. Ascend from sup.olivary
nuclei to form the lateral lemniscus
in pons, then ascend to end in
inferior colliculus of midbrain.
Some Fs. end in nucleus of lateral
lemniscus in pons to establish reflex
connections with motor trigeminal &
facial nuclei, mediating cotraction of
tensor tympani & stapedius Ms. In
response to loud noise.
2nd order neurones arise
from cochlear nuclei into
pons, some Fs. Cross to
opposite side as trapezoid
body.

The inferior colliculus sends
axons to medial geniculate
nucleus of thalamus.
3rd order neurone : axons
arise from MGN pass through
internal capsule to primary
auditory cortex, which is
located in Heschl’s gyri lying
in superior temporal gyrus and
hidden within the lateral fissure
Auditory association cortex
( Wernick’s area) is an area of
temporal lobe surrounding the
primary auditory cortex , in
which the auditory information
is interpreted ( for knowing the
meaning of sounds).

Lateral aspect of cerebral
hemisphere
Note primary auditory cortex & Wernicke’s area in
superior temporal gyrus.

Acoustic Neuroma :
 It is a benign tumour of vestibulocochlear
nerve leads to compression of the nerve &
adjacent structures in cerebello-pontine angle.
 So, there is attacks of dizziness & deafness.
 With expansion of tumour, ataxia (disturbances
of voluntary movement) & paralysis of cranial
Ns.(especially V-VII) and the limbs follow due to
damage of pyramidal Fs.

IX : Glossopharyngeal Nerve :
Glossopharyngeal nerve nuclei &
their central connections
It is a mixed N. ,attached
lateral to olive in rostral
medulla and leaves the skull
through jugular foramen.
It receives afferent Fs. From :
1-Receptors of general sensation
in pharynx, post.1/3 of tongue,
eustachian tube & middle ear.
2- Taste buds of pharynx &
post.1/3 of tongue.
3- Chemoreceptors in carotid
body & Baroreceptors in the
carotid sinus.

IX : Glossopharyngeal Nerve Fibres :
their central connections. Red=
motor, brown=parasymp.,blue=sensory
1-Afferent Fs. for general
sensation : end in trigeminal
sensory nucleus.
-Fibres carrying touch sensation
from back of tongue +pharynx are
important for mediating gag reflex,
through connection with nucleus
ambiguus & hypoglossal nucleus.
2-Afferent visceral (chemo-&
baroreceptors) & taste Fs. :
end in nucleus solitarius of
medulla.

IX : Glossopharyngeal Nerve Fibres :
their central connections. Red= motor,
brown=parasymp.,blue=sensory
3-Efferent motor Fibres :
arises from its motor nucleus in the
rostral part of nucleus ambiguus of
medulla to supply stylopharyngeus
involved in swallowing.
4-Efferent Parasympathetic
Fibres : arises from inferior salivary
nucleus of rostral medulla to synapse
in otic ganglion, then via post-
ganglionic Fs.innervate parotid gland.

X : Vagus Nerve :
Vagus nerve Nuclei & their
central connections.
It is mixed nerve, attached
lateral to olive of medulla caudal
to glosso-pharyngeal N. in groove
between olive & inf.cerebellar
peduncle.
It recevies afferent Fs.from :
1-Receptors for general sensation
in pharynx, larynx, tympanic
membrane, ext.acoustic meatus.
2- Chemoreceptors in aortic
bodies and baroreceptors in aortic
arch.
3-Receptors in thoracic &
abdominal viscera.

X : Vagus Nerve Fibres :
Vagus nerve Nuclei & their central
connections.
1-Afferent Fs.for general
sensation : end in sensory nucleus
of trigeminl and - visceral sensory
afferents end in nucleus solitarius.
2-Efferent Motor Fs. : arise from
nucleus ambiguus of medulla
(main motor nucleus of vagus) to
innervate Ms. of soft palate,
pharynx, larynx to control
swallowing and speech.
3-Efferent Parasymp. Fs. : arise
from dorsal motor nucleus of
vagus to supply CVS, RS, & GITS.

XI :Accessory Nerve :
Diagram of caudal medulla & rostral spinal
cord to illustrate origin and course of vagus
& accessory nerves.
It is purely motor , consists of
cranial part & spinal part.
The cranial part emerges from
lateral aspect of medulla below vagus
N. It arises from caudal part of
nucleus ambiguus of medulla.
At the level of jugular foramen it
joins vagusN. to supply Ms. of soft
palate, pharynx & larynx.
Spinal root of accessory arises
from upper 5 cervical spinal cord
segments. It ascends to the side of
medulla to join the cranial root till
the jugular F., it separates to supply
sternomastoid & trapezius Ms.

XII : Hypoglossal Nerve :
T.S.of medulla to illustrate origin
& course of hypoglossal nerve.
It is purely motor , supplying all
extrinsic & intrinsic Ms. of tongue
except palatoglossus (by pharyngeal
plexus).
It arises from hypoglossal nucleus in
medulla ( beneath floor of 4th V.).
It emerges from M.O. between olive
& pyramid.
It also receives coticobulbar Fs. from
contralateral motor cortex, which
subserve voluntary movements of
tongue as occur in speech.

Motor neurone disease and lesions
of cranial nerves IX-XII :
 Occures in those over 50 years due to chronic degeneration
of cortico-bulbar tracts projecting to nucleus ambiguus
(sends motor Fs.in 9,10,11 nerves) & hypoglossal nucleus ,
leading to dysphonia (difficulty in phonation), dysphagia
(difficulty in swallowing) , dysarthria ( difficulty in
articulation) and weakness & spasticity of tongue
(pseudobulbar palsy).
 There is also degeneration of nucleus ambiguus &
hypoglossal nucleus themselves, leading to
dysphonia,dysphagia, dysarthria and weakness, wasting &
fasciculation of tongue (bulbar palsy).
 IX-XII nerves can be damaged by tumours in skull
foramina, lead to dysphonia, weakness, wasting &
fasciculation of tongue and depression of gag reflex +
wasting of sternomastoid & trapezius Ms.

Cranial Nerves & Nuclei: Anatomy and Functions

Cranial Nerves & Nuclei: Anatomy and Functions

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