the cranial nerves

Done by: Dr Nina Emil Musallam

Clinical aspect
 Fracture in the anterior cranial fossa may cause a CSF
leakage through the nose (CSF rhinorrhea), from
tearing the meningeal sleeves that ensheathe the
olfactory bulb
 Complete anosmia if all the filaments on one side are
torn

- The oculomotor nucleus which is situated ventral to the aqueduct
of the midbrain in the central grey matter at the level of the superior
colliculus.
- It is the most rostral of the nuclei in the somatic motor column.
- It appears likely that some of the axons cross the midline to join the
oculomotor nerve of the opposite side
- The GVM or parasympathetic, preganglionic fibres for the sphincter
pupillae and ciliary body begin in the Edinger-Westphal nucleus
- Enter the tendinous ring.

 The oculomotor nerve supplies:
1) the extraocular muscles, with the exception of the
superior oblique and lateral rectus
2) most of levator palpebrae superioris.
3) parasympathetic fibres to the sphincter pupillae
and ciliary muscle of the eyeball.

The Trochlear nerve
 Its fibres begin in the trochlear nucleus which lies in the central
grey matter of the midbrain at the level of the inferior colliculus.
 It is immediately caudal to, and in line with, the oculomotor nucleus.
 The trochlear nerve is unique in that it is the only cranial nerve which
emerges from the dorsal surface of the brainstem and in which all
the fibres cross the midline.
 The fibres leave the trochlear nucleus by running dorsally and
medially behind the aqueduct, where they decussate with the fibres
from the opposite nucleus, to emerge from the midbrain below the
contralateral inferior colliculus.
 At the lateral wall of the cavernous sinus, It runs first below the 3rd
cranial nerve then above it at the anterior end of the sinus
 It enter SOF then lateral to the tendinous ring and passes medially
over the LPS muscle
 The trochlear nerve innervates the superior oblique muscle

Trigeminal nerve:
Has large sensory root and small motor root which both pass
below the tentorium cerebella to the trigeminal cave;
--Large sensory (GSA)through its 3 divisions
The sensory root is continuous with the trigeminal ganglion which
is located within the trigeminal cave in the middle cranial fossa.
The sensory root consists of fibers of cell bodies in the trigeminal
ganglion which enter the chief sensory and spinal nuclei, and the direct
fibers from mesencephalic nuclei.
--Small motor root(SVE) through its mandibular division
The motor root emerges cranial and medial to the sensory root and
runs beneath the ganglion to join the mandibular division.

Trigeminal nuclei:
1) the chief sensory nucleus of the trigeminal which is
located in the dorsolateral part of the tegmentum of the
pons (i.e. in the somatic sensory column). For
discriminative touch, simple touch and pressure.
2) nucleus of spinal tract Immediately medial to the spinal
tract of trigeminal, which is continuous rostrally with the
chief sensory nucleus and caudally with the dorsal grey
horn of the upper part of the cord. It is situated, in the
somatic sensory column. The spinal nucleus can be divided
into three main parts—caudal, intermediate, and
rostral.

a) The caudal part
for pain and temperature.
has a similar cellular composition to the dorsal grey horn of
the spinal cord (laminae I-IV).
The most caudal part of the nucleus receives pain and temperature fibres
from the upper cervical nerves, as well as from the trigeminal.
The somatotopic representation of the face in the caudal part of the
spinal nucleus is a lamellar’ onion-like’ representation. It is believed to
apply to only the sensations of pain and temperature.
the inner most or circumoral zone is represented in the upper most
segment of the caudal subnucleus
the outer most zone (stretching from the lower border of the chin across
the posterior parts of the cheeks and the anterior parts of the auricles
to the top of the scalp) being represented in the lower most segment of
the subnucleus

b) The intermediate part
for simple touch and pressure
also receiving pain fibres from the teeth.
c) rostal part
simple touch and pressure
 Both intermediate and rostral parts of the nucleus
contain numerous small and medium sized cells.

3) mesencephalic nucleus
- Rostrally to the chief sensory nucleus, into the lateral part
of the central grey matter of the midbrain.
- The cells in this nucleus are those of pseudounipolar first-
order sensory neurons for proprioception and are unusual
in that they are located in a central nucleus not in a sensory
ganglion.

4)motor nucleus
- Has the special visceral motor neurons
- Medial to chief sensory trigeminal nucleus
the most rostral nucleus in the special visceral motor column
- It also contains special visceral motor neurons to the
muscles derived from the first pharyngeal arch.
- As it leaves the brainstem the trigeminal contains no
general visceral motor neurons but some of its peripheral
branches give passage to such fibres received through
communications with the facial and glossopharyngeal
nerve

Sensory pathway of trigeminal
nerve:
The trigeminal ganglion mostly contains the first-order sensory
neurons
The central processes for touch →the sensory root of the nerve→
brainstem→ large diameter and small diameter;
-Large diameter is for discriminative touch→ end in the chief
sensory nucleus
-Some of the smaller diameter processes for simple touch and
pressure also give branches→ which end in the chief nucleus.
Most of the central processes for simple touch,pressure, pain and
temperature→the brainstem→ turn caudally →spinal tract of
the trigeminal.

Spinal tract of trigeminal nerve:
-descends through the brainstem and into the upper three
segments of the spinal cord.
-gradually diminishes in a caudal direction as its fibres
terminate at successive levels in the nucleus.
-There is a somatotopic arrangement of the fibres in the
spinal tract;
the ophthalmic division of the trigeminal run in its ventral
part, the maxillary division in its
intermediate part.
the mandibular division in its dorsal part.

 The chief and spinal nuclei have the second-order neurons
→ ventral posterior nucleus of the thalamus mainly in the
contralateral ventral trigeminothalamic tract.
Smaller numbers of fibres from the chief nucleus travel to
the thalamus in the dorsal trigeminothalamic tract of
both sides.
The ventral and dorsal tracts are often referred to together
as the trigeminal lemniscus.
Efferents from the spinal nucleus also connect with the
motor nuclei of the cranial nerves for reflex responses
to stimulation of trigeminal sensory fibres.

Most of the peripheral processes of these cells leave the
brainstem in the motor root of the trigeminal nerve
→the mandibular division →
neuromuscular spindles in the jaw muscles
and to endings in the jaw joint
and in the supporting tissues of the lower teeth.
A lesser number are believed to travel through the
sensory root and the ganglion →the maxillary division
to endings in the supporting tissues of the upper teeth
and palate.

 The mesencephalic nucleus receives proprioceptive
fibres from neuromuscular spindles in the extraocular
muscles,
and from spindles in the facial, lingual, and laryngeal
muscles
The central processes of the neurons whose cell bodies are
located in the mescencephalic nucleus contact
-cells in the trigeminal motor nucleus for reflex control of
jaw movements
-cells in the reticular formation from which axons pass to
the thalamus.

Motor trigeminal pathway:
Afferents from both the ipsilateral and contralateral
corticobulbar tracts→ trigeminal motor nucleus→
efferents run in motor root of the nerve→ mandibular
division→ muscles derived from the mandibular arch
It is connected with the sensory nuclei of the trigeminal
nerve for reflex responses to stimulation of the area of
sensory distribution of the nerve.

Branches of trigeminal nerve:

The Ophthalmic nerve:
Runs forward in the lateral wall of the cavernous sinus
Below the trochlear nerve, it picks up sympathetic
fibres from the plexus around the internal carotid
artery. (for the dilator papillae muscle)
1) meningeal branch: at the anterior end of the sinus
2)lacremal nerve → superior orbital fissure
3)frontal nerve→ superior orbital fissure
4) nasociliary nerve → superior orbital fissure


Passing lateral to the tendinous ring
Proceeds along the upper part of the lateral wall of the
orbit→ picking up a secretomotor branch from the
zygomaticotemporal branch of the zygomatic nerve→
lacremal gland
Sensory to the skin at lateral end of the upper eyelid and
both palpebral and ocular surfaces of the corresponding
conjunctiva.
The lacrimal nerve

The frontal nerve
 SOF
 Lateral to the tendinous ring
 Runs forwards and above LPS muscle and behind the
superior orbital margin, as large nerve.
 It divided to
1)the supraorbital nerve: frontal sinus
notches the orbital margin
Upper eyelid (skin and conjunctiva)
All forehead Except central trip
Frontal scalp up to the vetrex
2)the supratrochlear nerve: upper lid,conjunctiva and a
narrow strip of forehead skin alongside the midline

The nasociliary nerve
 SOF
 Runs through the tendinous ring between the two division of
the oculomotor
 It passes forwards and medially above the optic nerve, below
SR and SO muscles
 Branches:
1) Anterior ethmoidal nerve external nasal nerve
2) Infratrochlear nerve
3) Posterior ethmoidal nerve
4) Communicating branch
5) long ciliary nerve

 Anterior ethmoidal nerve
medial wall of the orbit anterior ethmoidal foramen
descends alongside crista galli nose external nasal
nerve
Supplies:
-mucous membran of the anterosuperior
part at the lower margin of nasal bone
-Skin of ala
-tip and vestibule of the nose

 The infratrochlear nerve
-branch off the nasociliary before it enters the
anterior ethmoid foramen
-continues forward below the trrochlea of SO
tendon
supplies:
-skin and conjunctiva of the medial end of the
upper eyelid
-skin over the brige of the nose.

 The posterior ethmoidal nerve:
- branches off the nasociliary proximal to the
infratrochlear nerve
- enter thposterior ethmoidal foramen
supplies:
posterior ethmoidal air cells
Sphenoidal sinus

 Communicating branch
it’s the sensory root of the ciliary ganglion
it’s fibers passes through the ganglion and via the short
ciliary nerve to provide sensory fibers to the eye including
the cornea but not the conjunctiva
 Long ciliary nerve:
Usually two
Run forward to enter the sclera
Carry sympathatic fiber to the dilator pupillae muscle
And sensory to the eye including the cornea but not the
conjunctiva

Maxillary Nerve
 Runs forward in the lateral wall of the cavernous
sinus, below the opthalmic nerve
 Gives off memingeal branch in the cranium
 Then foramen rotundum pterygopalatine fossa
IOF ( as ION)

Maxillary in the pteygopalatine
fossa

In the pterygopalatin fossa:
 Two ganglionic branches connect the maxillary nerve
with the pterygopalatine ganglion
* As the contain sensory fibers to the nose, palat, and the
pharynx.
* Also contain postganglionic parasympathatic fibers to
the lacremal
 nerve of pterygoid canal (vidian) which are
postganglionic fibers enter the Pterygopalatine ganglion
and mingle with its branches

Branches of maxillary nerve : The zygomatic nerve
Arise in the pterygopalatine fossa IOF
1)zygomaticofacial nerve outside
supplies the skin over the zygomatic bone
2) zygomaticotemporal pierces the temporal facia
supplies the skin over the zygomatic arch
The postganglionic parasympathatic fibers from the vidian nerves
pass through the zygomatic nerve via the two ganglionic
branches in the pterygopalatine fossa. This secretomotor fibers
are transmitted to the lacremal gland via the connection of the
zygomatic nerve of maxillary division with the lacremal nerve of
opthalmic division.

 posterior superior alveolar nerve:
-Arises in pterygopalatine fossa pterygomaxillary
fissure posterior wall of the maxilla
-Supplies:
Maxillary sinus
Upper molar teeth
Adjacent gum of the vestibule

 Infraorbital nerve:
passes forward along floor of the orbit groove canal IOFr
Infraorbital gives off nerves in the infraorbital canal:
-Anterior superior alveolar nerve
-Middle supperior alveolar nerve
Supplies:
Maxillary sinus (directly via middle and anterior superior alveolar
nerves)
Upper premolar teeth (middle)
Upper canine and two incisors
Anterior inferior part of the lateral wall of the nose
Adjacent floor of the nose
The infraorbital nerve, on emerging between the levator labii superioris
and levator anguli oris, has a communicating branches with facial nerves

The Mandibular nerve
 Passes down through foramen ovale as separate
sensory and motor root
 Joining occurs:
Just below the foramen ovale
In the infra temporal fossa
Between the upper head of lateral pterygoid and tensor
palati mucles
Where the otic ganglion lies medial to the nerve

Mandibular branches:
 Main trunk:
1) meningeal branch( nervus spinosus):
pass up through foramen ovale or foramen
spinosum
2) nerve to medial pterygoid muscles:
gives branches to tensor palati and tensor tympani

Anterior division:
 All motor Except one sensory
1) nerve to lateral pterygoid muscle
2) deep temporal nerve (two) :
above upper head of the lateral pterygoid muscle then deep to temporalis
3) nerve to maseter muscle :
above upper head of lateral pterygoid muscle then larally to mandibular
notch to masseter muscle.
gives off branch to mandibular joint
4) buccal nerve: only sensory branch
between the two heads of lateral pterygoid muscle
pierce the buccinator muscle
supplies:
small area of the cheek
mucous membrane adherent to the deep surface of the muscle
vestibular gum of the three mandibular molar teeth
The buccal nerve carries secretomotor fibers from otic ganglion to the
mucous gland in the mouth

Posterior division:
 All are sensory Except one motor
1) auriculotemporal nerve:
has two roots that pass back around middle meningeal artery
picks up secretomotor fibers from otic ganglion to parotid
gland
passes deep to the neck of the mandible and gives the major
sensory supply to mandibular joint
supplies:
- the external acoustic meatus
- external surface of the auricle above
- skin of temporal region

2) Inferior alveolar nerve:
- deep down to the lower head of lateral pteygoid muscle
- on the lateral surface of the medial pteygoid muscle
- lying between the mandible and sphenomandibular ligament
- before entering the mandibular foramen it gives off the mylohyoid
nerve
- on entering the mandibular foramen it runs infront of alveolar artery
and vein
- in the mandibular canal it supplies the mandibular molar teeth and
gives terminal branches:
mental nerve : for lower premolars and through mental foramen to gum
and lower lip
carries fibers from otic to lower labial glands
incisive nerve : for canine and incisors
3) The mylohyoid nerve
which passes forward below MHM to supply MHM and Anterior belly
of digastric and submental skin.

4) lingual nerve:
- Joining chorda tympani 2cm below base of the skull
- Curves down on the medial pterygoid infront of IVN
- Crosses the submandibular duct
Supplies:
General ensation to the anterior 2/3 of the tongue and floor
of the mouth
The submandibular ganglion is suspended by lingual nerve
and the postganglionic fibers rejoin the lingual nerve to
transport to salivary glands of the mouth

Clinical aspect:
 The most common condition is trigeminal neuralgia that affect the
sensry part
pain in the V2,V3 more than V1
compression of trigeminal nerve adjacent to the pons by contact with
the vessels
 cerebrovascular accidents, such as strokes
 If the motor nucleus is damaged there will be paralysis of the muscles
of mastication with the result that on opening the mouth the jaw will
deviate to the side of the lesion due to the unopposed contraction
of the opposite lateral pterygoid muscle.
 The trigeminal nerve may also be involved in shingles (Herpes zoster),
caused by reactivation of the virus which lies latent in sensory nerve
ganglia following a previous infection of chickenpox.
the lesions may occur on the cornea of the eye and may be followed by
scarring with permanent impairment of vision.

The abducens nerve
The abducent nucleus is situated in the grey matter
forming the floor of the fourth ventricle.
Fibres from the motor nucleus of the facial nerve loop
dorsal to the abducent nucleus to form the facial
colliculus.
The abducent fibres run ventrally through the pons to
emerge at the junction of this part of the brainstem
with the medulla.
The nerve has a long intracranial course before entering
the orbit through the superior orbital fissure. It
supplies the lateral rectus muscle.

The facial nerve
Components:
 Motor (SVE) bulk one : 2nd pharyngeal arch muscles;
muscles of the face
scalp
stapedius muscle
posterior belly of digastrics muscle
stylohyoid muscle
 Secretomotor (GVE) parasympathetic:
Submandibular and sublingual salivary gland
The lacremal gland and glands of nose and palate,
paranasal air sinuses, nasopharynx
 Sensory (SVA) largest: taste from anterior 2/3 of tongue, from floor of
the mouth and palate
 There are also a few cutaneous (somatic sensory) fibres from a small
area around the external acoustic meatus

Facial pathway Intracranial:
The main facial nerve (large motor root of facial nerve)
emerges at the lower border of the pons and above the
olive.
The nervus intermedius(small sensory root of facial nerve)
emerges between the pons and the inferior cerebellar
peduncle, near the vestibulocochlear nerve.
The nervus intermedius, with the main part of facial nerve,
passes laterally in the cerebellopontine angle through the
pontine cistern,and they enter the internal acoustic meatus
with the vestibulocochlear nerve.

The intracranial course :
Internal acoustic meatus;
The main part of facial nerve lies on the upper surface of 8th cranial nerve,
with the nervus intermedius in between
Running laterally in the petrous bone
inner ear
middle ear →
sharp posterior bend ,the genu. Leading to form a Geniculate ganglion →
runs back in the medial wall of middle ear, above the promontory and
just below the bulge of the lateral semicircular canal→ curves
downwards behind the middle ear, deep to the aditus to the antrum→
passes vertically down the facial canal.

The extra carnial course:
The facial nerve emerges from stylomastoid foramen as a
purely motor nerve and passes through the parotid
gland.

The intracranial branches that arise
in the petrous bone:
1)The greater petrosal nerve
2)The nerve to stapedius
3)Chorda tympani

1) The greater petrosal nerve:
Consisting of nervus intermedius fibers
Leaves the ganglion and travels forward medially at 45⁰ slant through the
petrous bone.
It merges from anterosuperior surface of the petrous bone and runs
forwards in a groove on the bone, between the two layers of the dura
mater.
The nerve passes beneath the trigeminal ganglion and reaches foramen
lacerum where it is joined by the deep petrosal nerve from the
sympathetic plexus on the internal carotid artery.
They pass forwards through the pteryoid canal then this nerve of
pterygoid canal emerges into the pterygopalatine fossa and enter
pterygopalatine ganglion.

pterygopalatine ganglion has sensory, parasympathetic and
sympathetic roots
1-paraymathatic root: the secretomotor fibers which come from
the nervus intermedius by the greater petrosal nerve.
The postganglionic secretomotor fibers are distributed with the
branches of the ganglion to nose, paranasal sinuses hard and soft
palates and nasopharynx. Lacrematory postganglionic fibers join
the maxillary nerve and enter the orbit in its zygomatic branch.
2- taste fibers from the soft palate
3- sympathetic fibers pass straight through the ganglion and it’s
postganglionic fibers from superior cervical ganglion and travel
through cervical plexus to deep petrosal nerve.
4- sensory root, from maxillary nerve through sphenopalatine
nerve.
The pterygopalatine ganglion:

2) The chorda tympani:
Consisting of nervus intermedius fibers
Leaves the facial nerve in the facial canal 6 mm above the stylomastoid
foramen
Pass through the posterior wall of the middle ear.
It runs forward between the mucous membrane and tympanic
membrane, crossing the neck of the malleus.
Leaves through the anterior wall of the middle ear and emerges at the
medial end of the petrotympanic fissure.
Then grooves the medial side of the spine of sphenoid
Slopes downwards and forwards to join the lingual nerve in the
infratemporal fossa.
By the lingual nerve, its taste fibers are taken to the anterior 2/3 of the
tongue.
Its secretomotor fibers rely in the submandibular ganglion for
submandibular glands and glands in the floor of the mouth cavity.

3)The nerve to stapedius:
Is given off in the facial canal

The extracranial branches:
1- posterior auricular nerve for occipital belly of
occipitofrontalis muscle
2- nerve to posterior belly of digastrics muscle
3- nerve to stylohyoid muscle
4- five groups of branches given off within the paroid gland
for facial muscle and platysma.

Sensory pathway of facial nerve:
geniculate ganglion is the first-order sensory neurons
Taste pathway:
The central processes of the taste fibres→ sensory root → Brainstem→
turn caudally in the tractus solitaries*→ the gustatory nucleus**→ to
the ventral posterior nucleus of the thalamus (bilaterally) third-order
neurons→ pass to the taste area in the lower part of the postcentral
gyrus.

*the tractus solitaries
where they are joined by taste and general visceral sensory fibres
from the glossopharyngeal and vagus.
**gustatory nucleus:
The rostral part of the tractus nucleus which lies
immediately alongside the tractus solitaries
receives the taste fibres from the tract and is situated in the
special visceral sensory column
The nucleus has numerous connections with the hypothalamus
and with the motor nuclei of the cranial nerves, especially the
salivatory nuclei and the dorsal nucleus of the vagus, for reflex
responses to taste.

The peripheral processes of the taste fibres which join the facial
nerve are distributed through:
- the greater petrosal branch to the palate
- the chorda tympani to the anterior two-thirds of the tongue.

General sensory pathway:
The central processes of the cutaneous fibres →sensory
root→ brainstem→
the spinal tract of the trigeminal nerve →spinal tract
nucleus.
The peripheral processes are distributed to a small area of
skin on the auricle and in the external acoustic meatus and
to part of the ear drum through communicating branches
which leave the facial nerve at its exit from the
stylomastoid foramen and pass to the greater auricular and
auriculotemporal nerves.

Motor pathway of facial nerve:
 Special visceral motor pathway:
Corticobulber fibers→ motor nucleus of facial nerve*→
* Motor nucleus of facial nerve:
- The upper part of the motor nucleus receives afferents from
the corticobulbar tracts of both sides.
-The lower part of the nucleus is supplied by crossed
corticobulbar fibres.
-The nucleus receives afferents from several other sources
including the tectum of the midbrain and the sensory
trigeminal nuclei.
-This is situated in the lateral part of the tegmentum of the
pons in the special visceral motor (SVM) column.

 The general visceral motor pathway of facial nerve:
The superior salivatory nucleus* (The preganglionic parasympathetic
neurons) → the sensory root of the nerve→
1) greater petrosal branch →synapse in the pterygopalatine ganglion
→postganglionic neurons which are distributed through the branches
of the ganglion to:
Fibres for the lacrimal gland and the glands of the nasal cavity,
nasopharynx, paranasal air sinuses, oral surface of the palate, upper lip
and upper part of cheek.
2) chorda tympani, join the lingual nerve→ submandibular ganglion
to:
Fibres for the submandibular and sublingual glands and the small glands
in the floor of the mouth

The superior salivatory nucleus:
-A collection of cells situated close to the motor nucleus,
in the general visceral motor column.
-Receives afferents from the nucleus of the tractus
solitarius, the trigeminal sensory nuclei, and the olfactory
system and hypothalamus.
-The part of the nucleus supplying the lacrimal gland (
the lacrimal nucleus) is connected with the trigeminal
spinal nucleus for the reflex production of tears in
response to corneal and conjunctival stimulation.

Clinical aspects
Facial paralysis is a common clinical condition
-upper motor neuron (or supranuclear) paralysis
-bell’s palsy lower motor neuron (infranuclear) paralysis.
1) UMN lesion:
Cause:
The most frequent cause is interruption of the supranuclear fibres from
the motor areas of the cerebral cortex as they travel through the
internal capsule on their way to the facial motor nucleus as a result of a
stroke.
Result:
Paralysis on the opposite side to the lesion.
 In the lower part of the face → drooping of the corner of the mouth
and puffing of the cheek.
 In the upper part of the face due to both innervations → able to→ to
wrinkle the forehead and close the eye on the contralateral side of the
lesion.

2) LMN lesion: Bell’s palsy
The commonest site is in the lower part of the facial canal due to:
compression of the facial nerve as a result of oedema of the tissues lining
the canal caused by a viral infection.
A) The victim suffers complete paralysis of all the muscles supplied by
the facial nerve, apart from stapedius which is innervated by a branch
which leaves the nerve higher up in the facial canal.
Result:
Paralysis on the ipsilateral side of the lesion drooping of the corner of the
mouth and puffing of the cheek, inability to close the eye and to
wrinkle the forehead on the affected side.
Recovery:
There is usually a slow and frequently incomplete recovery of muscle
function.
B) If the oedema spreads upwards along the facial canal it will involve the
chorda tympani resulting in ipsilateral loss or impairment of taste in
the anterior twothirds of the tongue and of secretion by the salivary
glands in the floor of the mouth.

C) If the lesion is situated proximal to the geniculate ganglion as a
result of neurofibroma of the vestibulocochlear nerve in the
internal acoustic meatus which compresses the facial nerve
leading to loss of all the function of facial nerve;
-The paralysis will involve stapedius, resulting in hyperacuity.
- impaired secretion of tears and loss of taste in the palate and
anterior 2/3 of the tongue and salivary gland secretion on the
affected side.
- paralysis in the face muscles
Other causes:
The facial nerve or its branches may be interrupted in the parotid
gland or face by trauma (including surgery).
Temporary facial paralysis follows the inadvertent introduction of
local anaesthatic solution into the parotid gland when
attempting to give an inferior alveolar block.

3)Temporary Facial paresis:
During the extradural operation in the middle cranial fossa
the greater petrosal nerve may be pulled on and cause a
small haemorrage or oedema at the geniculate ganglion
with consequent pressure on the facial nerve.

Notes:
There is an essential
similarity between the
functional arrangement
of the nuclei of the
cranial nerves in the
brainstem and of the
grey matter in the spinal
cord, reflecting the fact
that in both of these
regions:
The motor grey areas
develop from the basal
plates; and
The sensory areas
from the alar plates

Three major ways in which the dorsal cranial nerves differ from
the dorsal spinal roots:
 (1) the dorsal cranial nerves do not fuse with the
corresponding ventral nerves.
 (2) the general visceral motor fibres leaving the brain (all
parasympathetic) pass in the dorsal cranial nerves- in the
spinal region, by contrast, the general visceral motor fibres
(mostly sympathetic) leave the spinal cord in the ventral
roots.
 (3) each dorsal cranial nerve has become associated with a
specific pharyngeal arch and carries motor fibres to the
muscles from that arch.

Summary of the types of neuron that may be
found in the cranial nerves:
 the ventral cranial nerves (III, IV, VI, and XII, should contain somatic motor fibres.
 the dorsal cranial nerves (V, VII, IX, and X + cranial XI) should contain
somatic sensory (cutaneous sensation and proprioception),
visceral sensory (general visceral sensory and special visceral sensory or taste),
general visceral motor (parasympathetic), and
special visceral motor (branchiomotor) fibres.
But a few exceptions occur; In particular:
 the oculomotor contains a general visceral motor component (parasympathetic fibres to the
eyeball)
 several of the dorsal cranial nerves are lacking one or more of their components.
 The vestibulocochlear nerve probably represents fused components of the facial,
glossopharyngeal, and vagus nerves which supplied that part of the lateral line organ in
the head region which became, during evolution, the internal ear.

 One column can be considered as extending upwards from thedorsal grey horn.
This contains nuclei associated, like the dorsal grey horn itself, with somatic sensory
neurons that is the various sensory nuclei of the trigeminal nerve.
 A second column ascends in line with the ventral grey horn and contains nuclei in which
are found, as in the ventral horn, cell bodies of somatic lower motor neurons - that is the
nuclei of the oculomotor, trochlear, abducent, and hypoglossal nerves.
 Between the somatic sensory and somatic motor columns are the visceral sensory and
visceral motor columns. They occupy the same general position within the brainstem as
does the lateral grey horn in the thoracolumbar segments of the cord.
 In the brainstem region, however, both of the visceral columns are further subdivided into
general and special. As would be expected, the sensory visceral columns lie dorsal to the
motor visceral columns and within each pair the special column lies further from the
midtransverse plane than does the general column.
 Hence the sequence of visceral columns in a dorsoventral direction is special
visceral sensory, general visceral sensory, general visceral motor, and special
visceral motor.

 The special visceral sensory column contains the rostral part of the nucleus of
the tractus solitarius. The taste fibres, which are conveyed to the brainstem in
the facial, glossopharyngeal, and vagus nerves, end here.
 The general visceral sensory fibres arriving at the brainstem, principally in the
vagus, but also in the glossopharyngeal nerve, terminate in the caudal part of
the nucleus of the tractus solitarius.
 The general visceral motor column contains the superior and inferior salivatory
nuclei and the dorsal nucleus of the vagus.
The cell bodies of the preganglionic parasympathetic neurons, which are
distributed in the facial, glossopharyngeal, and vagus nerves, begin in these
nuclei.
 In the midbrain there is a further general visceral motor nucleus associated
with the oculomotor nerve. This, the Edinger-Westphal nucleus, provides
preganglionic parasympathetic fibres for the innervation of the eyeball.
 The special visceral motor column contains the motor nuclei of the trigeminal
and facial nerves, for the muscles of the mandibular and hyoid arches
respectively, and the nucleus ambiguus from which fibres pass in the
glossopharyngeal, vagus, and cranial accessory nerves to the muscles of the
remaining arches.

 In the pons and upper medulla the dorsoventral arrangement of
the columns is disturbed by the presence of the fourth ventricle.
 The enlargement of the central canal to form the ventricle takes
place principally in a dorsal direction so that the grey matter
originally located dorsal to the canal is displaced laterally.
In other words the columns in the upper part of the medulla and in
the pons become arranged in a medial to lateral, rather than a
ventral to dorsal, sequence but their order with respect to each
other remains unchanged.
The position of the columns in this part of the brainstem can be
related to the sulcus limitans in the floor of the fourth ventricle
which represents, just as it does in the spinal cord, the dividing
line between the alar and basal plates.

 References:
- Anatomy for dental students, 3rd edition; section 5,
Central nervous system. Part 6 “cranial nerves ”.
- Last’s anatomy; chapter 7, Central nervous system.
part 6”summary of cranial nerves” and part 7
“summary of cranial nerve lesions”.

the cranial nerves

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