3. 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
4. The optic nerve
5. The oculomotor nerve
6. - 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.
7. 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.
8. Eye movements
9. Clinical aspect
10. The Trochlear nerve
11. 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
12. 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.
13. 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 partscaudal, intermediate, and
rostral.
14. 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
15. 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.
16. 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.
17. 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
18. 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 temperaturethe
brainstem turn caudally spinal tract of the trigeminal.
19. 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.
20. 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.
21. 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.
22. 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.
23. 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.
24. Branches of trigeminal nerve
25. 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
26. 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
27. 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
28. 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
29. 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
30. 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.
31. The posterior ethmoidal nerve: - branches off the
nasociliary proximal to the infratrochlear nerve - enter
thposterior ethmoidal foramen supplies: posterior ethmoidal air
cells Sphenoidal sinus
32. Communicating branch its the sensory root of the ciliary
ganglion its 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
33. The maxillary nerve
34. Maxillary nerve
35. 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)
36. Maxillary in the pteygopalatine fossa
37. 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
38. Maxillary branches
39. 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.
40. 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
41. 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
42. The mandibular nerve
43. 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
44. 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
45. 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
46. 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
47. 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.
48. 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
49. 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.
50. The abducens nerve
51. 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.
52. Clinical aspect
53. The facial nerve
54. 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
55. 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.
56. 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.
57. The intracranial course :
58. The intracranial course :
59. The extra carnial course: The facial nerve emerges from
stylomastoid foramen as a purely motor nerve and passes through the
parotid gland.
60. The intracranial branches that arise in the petrous bone:
1)The greater petrosal nerve 2)The nerve to stapedius 3)Chorda
tympani
61. 1) The greater petrosal nerve: Consisting of nervus
intermedius fibers Leaves the ganglion and travels forward medially
at 45 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.
62. 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 its 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:
63. 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.
64. 3)The nerve to stapedius: Is given off in the facial
canal
65. 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.
66. 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.
67. *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.
68. 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.
69. **gustatory nucleus:
70. 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.
71. 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.
72. 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
73. 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.
74. Clinical aspects Facial paralysis is a common clinical
condition -upper motor neuron (or supranuclear) paralysis -bells
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.
75. 2) LMN lesion: Bells 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.
76. 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.
77. 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.
78. 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
79. 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.
80. 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.
81. 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.
82. 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.
83. 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.
84. References: - Anatomy for dental students, 3rd edition;
section 5, Central nervous system. Part 6 cranial nerves . - Lasts
anatomy; chapter 7, Central nervous system. part 6summary of
cranial nerves and part 7 summary of cranial nerve lesions.
