for dental students

1. Cranial nerves
AVANEETH RAM
1st YR PG
DEPT.OF
PAEDODONTICS.

2. Content
Embryology
Nerves basics and classification
Cranial nerves types
Insertion
Components
Functions
Clinical relevance
Conclusion
Reference

4. Introduction
Nerves emerges directly from the brain stem except
olfactory and optic from cerebrum of forebrain.
Each are paired and present on both sides
Numbered in romans depends on its definition in humans
and ordered according its emerges from front brain to
back
They consider as components of pns but 1 and 2 is of cns

5. Somatic
efferent CN
Nerves of
pharyngeal
arches
Special
sensory
nerves
Embryology
 Most of cranial and spinal sensory ganglion arise by differentiation of neural
crest cells.
 12 pairs forms at 5th and 6th week
 Embryonic origin as 3 groups

6.  A 3.1/2 w D 7 w
 B 4 w E 11 w
 C 5.1/2

8. 1. Somatic efferent cranial nerves
Cranial nerves IV,VI,XII and greater part of III are
homologous with ventral root of spinal nerves.
Origins – somatic efferent column of brain stem
CN XII ---resembles spinal nerves
by fusion of ventral root fibers of 3 and 4 occipital
nerve somatic fibers from hypoglossal nucleus ---consists
motor cells resembles ventral horns of spinal cord.
several groups of fibers leave the ventrolateral wall of medulla
it comes to progressively higher level with development
of neck.

9. CN VI --- arise from nerve cells in basal plate
passes from ventral to posterior surface of
third
preotic myotomes
from which lateral rectus thought to originate
CN IV --- from sfc of posterior part of midbrain
motor nerve emerges from brainstem dorsally
to
ventrally supply superior oblique.
CN III --- from first preotic myotomes supply most of
eye
muscles

10. 2. Nerves of pharyngeal arches
Cranial nerves V, VII, IX and X structures from these
arches are supplied by this nerve.
CN V from first pharyngeal arch
ophthalmic is not from this arch
it is chiefly sensory and is principle sensory nerve
for head
large trigeminal ganglion lies beside the rostral end
of pons its cell
derived from the most anterior part of neural crest.

11. Central process of cells in ganglion forms the large sensory
root
---enters at lateral portion of pons
ophthalmic ,maxillary and mandibular at peripheral
portion
sensory fibers ----skin of face lining of mouth and nose
motor fibers ---special visceral column in mitencephalon
fibers leave where sensory fibers enter and pass to
masticatory muscles and muscles from mandibular
prominence.

12. CN VII mostly motor fibers
from nucleus group of special visceral efferent
column in pons
small visceral component terminate peripheral
autonomic ganglion of head
sensory fibers from geniculate ganglion
central process enters pons
peripheral process pass to greater superficial
petrosal nerve via chorda tympanic nerve ----taste buds in
anterior 2/3rd of tongue

13. CN X by fusion of 4th and 5th pharyngeal arches
large efferent and afferent component
heart foregut and large part of midgut
superior laryngeal nerve 4th arch ---cricothyroid and
constrictor of pharynx
recurrent laryngeal nerve 5th arch ---various laryngeal
muscles
CN XI series of rootlets from cranial 5th or 6th cervical
segment of spinal cord
traditional cranial root fibers are now part of CN X ---
SCM and trapezius

14. 3.Special sensory nerves
CN I from olfactory organ
the neurons differentiate from cells in epithelial lining
of primordial nasal sac.
Central process of bipolar olfactory neurons collected
into branches to form
approx 20 olfactory nerves ---- around which cribriform
plate of ethmoid bone is developed
unmylinated nerve fibers end in olfactory bulb

15. CN II 2 kind of sensory fibers in 2 bundles as vestibular
and cochlear nerves
vestibular nerve ---semilunar ducts
cochlear nerve ---cochlear duct from special organ
develops
bipolar neurons of VN have cells in vestibular ganglion
central process terminate in vestibular nuclei on floor
of fourth ventricles
bipolar nerves of cochlear nerves in spiral ganglion
central process in ventral and dorsal cochlear nuclei in
medulla

16. Nervous system
A complex of interconnected systems in which larger systems
are comprised of smaller subsystems each of which have
specific structure with specific function.
Neurons are the basic elements
have cell body dendrites and axons(myelin sheath
neurilemma)
terminal end fibers at ends of axon transmit impulses leaving
neurons across synapses of other neurons.

17. 3 types
EFFERENT—CNS to muscle and glands(M)
AFFERENT—sensory receptor to CNS(S)
INTERNEURON—carry and process sensory
information

18. Neuroglial support protect connect and remove debris
Astrocytes
Oligocytes
Microglia

19. 2 major components
 CNS - made up of brain and spinal cord
 PNS – by nerves lead in and out of CNS

20. By
Avaneethram
first year

21. Olfactory nerve
Component sensory
Function smell
Origin olfactory receptor nerve
cells
Exit Cribriform plate of
ethmod

22. • Shortest
 Smell
 Similar to the optic nerve in its structure,
 It has a meningeal covering unlike CN III to XII.
 Embryologically derived from the otic placode (a
thickening of the ectoderm layer)
 Capable of regeneration.

24. RECEPTOR AND THE FIRST NEURON
a)The olfactory cells
 16- 20 million
 Lie in olfactory part of nasal mucosa
 Serves as receptor as well as the first neuron in the
olfactory pathway.

26. b)Second Neuron
The mitral and tufted cells in -olfactory bulb gives off fibers
form the olfactory tract -reach the primary olfactory area.
c)Third neuron
In the primary olfactory cortex
Includes the anterior perforated substance and several
small masses of grey matter around it.
d)Fourth neuron
Fibers arising in the primary olfactory cortex go to the
secondary olfactory cortex
located in the uncus and the anterior part of para
hyppocampal gyrus

29. CLINICAL RELEVANCE: ANOSMIA
 Sense of smell -Ab
 Sense foul smell tested seperately
 Allergic rhinitis causes temporary olfactory impairement
 Head injury: Olfactory bulbs may be torn away from the
olfactory nerves as these pass through cribriform plate.
 Presence of ascess in frontal lobe of brain
 Meningioma in the anterior crania fossa

30. Optic nerve
Component -sensory
Function -vision
Origin -back of eye
Exit -optic canal

31.  Transmits -special sensory information -sight
 Embryologically, developed from the optic vesicle.
 binocular , stereoscopic and coloured
 Due to its unique anatomical relation to the brain, the
optic nerve is surrounded by cranial meninges

32. FIELD OF VISION
-temporal and nasal field
-upper and lower field of vision
-total 4 fields of vision
upper temporal
lower temporal
upper nasal
lower nasal
-nasal fields smaller than temporal fields

34. -Fibres from nasal parts of the 2 retinae decussate to form
the optic chiasma and travel to contralateral side in the
optic tract
-fibres from the temporal hemiretinae continue ipsilaterally
in the optic tract
-

35. OPTIC TRACT
 Within the middle cranial fossa, optic nerves from each
eye unite to form optic chiasm.
 At the chiasm, fibres from the nasal (medial) half of each
retina cross over, forming the optic tracts:
LEFT OPTIC TRACT
contains fibres from the left temporal (lateral) retina,
and the right nasal (medial) retina.
RIGHT OPTIC TRACT
contains fibres from the right temporal retina, and the
left nasal retina.
 Each travels to its corresponding cerebral hemisphere to
reach the Lateral Geniculate Nucleus (LGN)
 a relay system located in the thalamus; the fibres
synapse here.

37. OPTIC RADIATION
 Axons from the LGN then carry visual information via a
pathway known as the optic radiation.
UPPER OPTIC RADIATION
 carries fibres from superior retinal quadrants
 It travels through the parietal lobe to reach the visual
cortex.
LOWER OPTIC RADIATION
 fibres from inferior retinal quadrants
 travels through temporal lobe, via pathway called
Meyers’ loop.
 Once at the visual cortex, the brain processes the
sensory data and responds appropriately.

39. VISUAL CORTEX
-optic radiation ends in striate area
-color , size, shape, motion , illumination and transparency
are appreciated separately
-Objects are identified by integration of these perceptions
with past experience
-Area of the visual cortex that receives impulses from the
macula is much larger and lies in posterior part

41. CLINICAL RELEVANCE: PITUITARY
ADENOMA
 Tumour of pituitary gland.
 Within middle cranial fossa, pituitary gland lies in close
proximity to optic chiasm.
 Enlargement of pituitary gland can affect the functioning
of optic nerve.
 Compression to optic chiasm particularly affects fibres
that are crossing over from the nasal half of each retina.
This produces visual defect affecting the peripheral vision
in both eyes, known as a bitemporal hemianopia.
 Partial Blindness
 Surgical intervention

43. -scotoma Lesion in the retina, certain point become blind
-Optic nerve damage-complete blindness
-Complete destruction of optic tract , lateral geniculate body
, optic radiation or visual cortex on one side results in
loss of opposite half of fields of vision
-Papilloedema- increased intra cranial pressure
-Optic neuritis- complete or partial loss of vision

44. Occulomotor nerve
Component -motor
Function -raises upper eye lid.
turns eyeball upward, downward
and medially.
constricts pupils
accomodates the eye
Origin -anterior surface of the midbrain
Exit -superior orbital fissure

45.  Motor and parasympathetic innervation to many ocular
structures
 Distributed to extra ocular muscles

47. ANATOMICAL COURSE
originates
from
anterior
aspect of
midbrain.
Moves
anteriorly,
passing below
the posterior
cerebral artery,
and above the
superior
cerebellar
artery and runs
forwards, on
the lateral side
of posterior
communicating
artery to reach
cavernous
sinus
nerve
pierces dura
mater --enters
the lateral
aspect of
the cavernous
sinus.
Within the
cavernous
sinus, receives
sympathetic
branches
from internal
carotid plexus
Frm anterior
part nerve

50. 2 division
enters the orbit
through middle
part of superior
orbital fissure
(nerve lies
between the
two divisions)
In orbit
smaller
upper division
divides into 3
branches-
medial rectus,
inferior rectus
and inferior
oblique
All branches
enter muscles
in occular
surfaces
except
inferior
oblique
muscle

52. CLINICAL RELEVANCE: OCULOMOTOR
NERVE LESION
 3 main anatomical causes of oculomotor nerve lesion:
Increasing intracranial pressure – compresses the
nerve
against temporal bone.
Aneurysm of posterior cerebral artery.
Cavernous sinus infection or trauma..

55.  Ptosis (drooping upper eyelid) – paralysis of levator
palpabrae superioris.
 Eyeball resting in ‘down and out‘ location – due to the
paralysis of the superior, inferior and medial rectus,
and the inferior oblique. The patient is unable to
elevate, depress or adduct the eye.
 Dilated pupil – unopposed action of dilator pupillae
muscle

56. Trochlear nerve
Component -motor
Function -assisting in turning eyeball downward
and
laterally
Origin -dorsum of midbrain
Exit -suprior orbital fissure
 smallest (by number of
axons)
 has longest intracranial
course.
 purely somatic motor
function.

57. Arises from trochlear nucleus of
brain
It runs anteriorly and inferiorly
within subarachnoid space before
piercing dura mater adjacent to
posterior clinoid process of
sphenoid bone.
moves along lateral wall of the cavernous
sinus before entering orbit of eye via
superior orbital fissure
ANATOMICAL
COURSE

59. CLINICAL RELEVANCE
Examination of the Trochlear Nerve
 Examined in conjunction with oculomotor and abducent
nerves by testing the movements of eye.
 The patient is asked to follow a point without moving
their head. The target is moved in an ‘H-shape’ and the
patient is asked to report any blurring of vision
or diplopia

60. PALSY OF THE TROCHLEAR NERVE
 Commonly presents with vertical diplopia,
exacerbated when looking downwards and inwards
 They are commonly caused by microvascular
damage from diabetes mellitus or hypertensive
disease.
 Other causes include congenital malformation, and
raised intracranial pressure.

61. Trigeminal nerve

62.  Largest and most complex
 Supplies sensations to the face, mucous membranes,
and other structures of the head.
 Motor supply to muscles of mastication .
 Exits brain by a large sensory root and a smaller motor
root
 Its a first pharyngeal arch derivative

63. NUCLERAR COLUMNS
A)General somatic afferent column
 Spinal nucleus of V nerve:
• takes pain and temperature sensation from most of the
face area which relay here.

64.  superior sensory nucleus of V nerve:
• Touch and pressure
 Mesencephalic nucleus:
• Receives proprioceptive impulses from muscle of
mastication, TMJ and teeth

66. SENSORY COMPONENT
 Sensation of pain, temp. touch and pressure from skin of
face, mucos membrae of nose most of tongue, paranasal
sinuses travel along the axon
 At the level of the pons, the sensory nuclei merge to form
a sensory root.
 The motor nucleus continues to form a motor root.
 In middle cranial fossa, the sensory root expands into the
trigeminal ganglion.
 Located lateral to the cavernous sinus, in a depression of
the temporal bone, known as the trigeminal cave.

68.  The peripheral aspect of the gives rise to 3
divisions: ophthalmic (V1),maxillary (V2)
and mandibular (V3).
 The motor root passes inferiorly to the sensory root,
along the floor of the trigeminal cave. Its fibres are
only distributed mandibular division.

69. MOTOR COMPONENT
 Fibres of motor root supply- four muscle of mastication
tensor veli palatini
tensor tympani
mylohyoid
anterior belly of digastic

70. 1.Ophthalmic Nerve
 Ophthalmic nerve gives rise to 3 terminal branches:
frontal
lacrimal
nasociliary
 frontal:
a)Supra trochlear:upper eye lid, conjunctiva, lower part of
forehead
b)supraorbital:Frontal air sinus, upper eyelid, forehead,
scalp till vertex

72.  Nasociliary
Anterior ethmoidal: middle and anterior ethmoidal siuses, medial
internal nasal, lateral internal nasal, external nasal
Posterior ethmoidal: sphenoidal air sinus, posterior ethmoidal air
sinus
Long ciliary: sensory to eye ball
Nerve to ciliary ganglion
Infra trochlear: both eyelids, sides of nose, lacrimal sac

77.  Lacrimal
 Lateral part of upper eyelid, conveys secetomotor fibres
from zygomatic nerve to lacrimal gland

79. MAXILLARY NERVE

80.  In the cranium
 Middle meningeal nerve in the meninges
 From the pterygopalatine fossa
 Zygomatic nerve(zygomaticotemporalnerve,
 zygomaticofacial nerve) through Inferior orbital fissure
 Nasopalatine -Sphenopalatine foramen
 Posterior superior alveolar nerve
 Palatine nerves (Greater palatine nerve, Lesser palatine
nerve)
 Pharyngeal nerve

81.  In the infraorbital canal
 Middle superior alveolar nerve
 Anterior superior alveolar nerve
 Infraorbital nerve
 On the face
 Inferior palpebral nerve
 Superior labial nerve

83.  Lower eyelid and its conjunctiva
 Cheeks and maxillary sinus
 Nasal cavity and lateral nose
 Upper lip
 Upper molar, incisor and canine teeth and the
associated gingiva
 Superior palate

84. Parasympathetic
 Lacrimal gland: Post ganglionic fibres from the
pterygopalatine ganglion (derived from the facial
nerve), travel with the zygomatic branch of V2 and
then join the lacrimal branch of V1.
 Nasal glands: Post-ganglionic fibres travel with the
nasopalatine and greater palatine nerves

86. MANDIBULAR NERVE
 These branches innervate the skin, mucous
membrane and striated muscle derivatives of
the mandibular prominence of the 1st
pharyngeal arch.
 Sensory supply:
 Mucous membranes and floor of the oral cavity
 External ear
 Lower lip
 Chin
 Anterior 2/3 of the tongue
 Lower molar, incisor canine teeth and gingiva

87.  Motor Supply:
 Muscles of mastication
 Anterior belly of the digastric muscle and the
mylohyoid muscle
 Tensor veli palatini
 Tensor tympani

88. Parasympathetic Supply:
 Submandibular and Sublingual glands: Post-
ganglionic fibres from submandibular ganglion travel with
lingual nerve to innervate these glands.
 Parotid gland: Post-ganglionic fibres from the otic
ganglion, travel with the auricotemporal branch of the V3
to innervate the parotid gland.

91.  Trunk
1)Meningeal
2)Nerve to medial pterygoid
tensor veli palatini
tensor tympani
medial pterygoid
 Anterior division
1)Deep temporal
2)Lateral pterygoid
3)Massetric
4)buccal
 Posterior division
1)Auriculo temporal
auricular
superior temporal
articular to TMJ
secretomotor to parotid
 Lingual; general sensation
from anterior two third of
tongue
 Inferior alveolar:lower teeth
and nerve to mylohyoid
mylohyoid
anterior belly of
digastric

92. DISTRIBUTION OF MANDIBULAR NERVE TO MUSCLES OF MASTICATION

93. CLINICAL TESTING
 Low pontine or medullary lesion will result in loss of pain
and temperature sensation while light sensation is
preserved
 Low pontine, medullary and cervical lesion produce a
characteristic onion skin distribution of pin prick and
temperature loss

94. MOTOR EXAMINATION
 Look for wasting or thinning of temporalis
muscle.There may be hollowing out of temporal fossa
 Ask the patient to press upper and lower teeth
together and feel for temporalis and masseter muscle
 Ask the patient to open the mouth.if the pterygoid
muscle is week , jaw deviates to the weak side

95. CORNEAL REFLEX
 The corneal reflex is the involuntary blinking of the
eyelids – stimulated by tactile, thermal or painful
stimulation of cornea.
 corneal reflex, ophthalmic nerve acts as afferent limb –
detecting the
stimuli.
facial nerve is the efferent limb- causing contraction of
the orbicularis oculi
muscle.
 If corneal reflex is absent, damage to ophthalmic nerve,
or facial nerve.

96. TRIGEMINAL NEURALGIA
Principle disease affecting sensory root is characterized by
pain in the area of distribution of maxillary and
mandibular division
The ganglion harbours the herpes zoster virus causing
shingles in the distribution of nerve

97. INFERIOR ALVEOLAR NERVE

98.  Panoramic radiograph revealed a strange radiolucency on the
coronoid processes bilaterally (a and c top circles) along with an
unusual radiolucency on the ramus of the mandible (b and d
bottom circles) which did not co-relate with the normal
radiolucency of the lingual fossa. a coronoid foramen right side; b
accessory mandibular foramen on lateral aspect of ramus; c
coronoid foramen left side; d accessory mandibular foramen on
lateral aspect of ramus

99.  Accidental discovery of these foramina will only
result in the procedural changes while operating
and surgical planning to avoid failure in
anaesthesia techniques by a regional block of
inferior alveolar nerve in particular, also operative
complications and its implications thereafter.
Bilateral 'coronoid foramina' with accessory foramina on the 'lateral aspect of
ramus' of mandible: an unseen variance discovery in humans.
Firdoose Chintamani Subhan N1. 2018 Jun;40(6):641-646. doi: 10.1007/s00276-
018-1984-6. Epub 2018 Feb 8

100. ABDUCENT NERVE

101. Enters the subarachnoid
space and pierces
the dura mater to run in
a space - Dorello’s
canal.
Travels through cavernous
sinus at the tip of petrous
temporal bone, before
entering orbit of eye through
superior orbital fissure
Within the bony
orbit, the nerve
terminates by
innervating
the lateral rectus
muscle

103. CLINICAL RELEVANCE:EXAMINATION
 Nerve is examined in conjunction with occulomotor and
trochlear nerves by testing the movements of the eye.
 The patient is asked to follow a point with eyes without
moving their head.
 The target is moved in an ‘H-shape’ and the patient is
asked to report any blurring of vision or diplopia .
 PALSY OF THE ABDUCENS NERVE
Any pathology which leads to downward pressure on
brainstem (e.g. brain tumour, extradural haematoma) can
lead to nerve damage

104. FACIAL NERVE

105.  Second pharyngeal arch.
 Motor: muscles of facial expression, posterior belly of the
digastric, stylohyoid and stapedius muscles.
 Sensory: None.
 Special Sensory: Provides special taste sensation to the
anterior 2/3 of the tongue.
 Parasympathetic: Supplies glands of head and neck,
including the submandibular, sublingual, nasal, palatine,
lacrimal and pharyngeal gland.

106. ANATOMICAL COURSE
 Divided into two parts:
Intracranial – course of nerve is within
cranium
itself.
Extracranial – course of nerve outside
cranium, through face and neck.

107. INTRA CRANIAL
nerve arises in
pons just medial
to 8 CN.It begins
as two roots; a
large motor root,
and small sensory
root .
The two roots
travel through
the internal
acoustic
meatus
Still within temporal
bone, roots leave
internal acoustic
meatus, and enter into
facial canal. Within
facial canal, 3
important events occur
2 roots fuse to form
facial nerve. nerve
forms
the geniculate
ganglion Lastly,
nerve gives rise to
greater petrosal
nerve , nerve
to stapedius
facial nerve
then exits facial
canal (and the
cranium)
via stylomasto
id foramen
1extracranial branch to
arise is posterior
auricular nerve.
Immediately distal to
this, motor branches
are sent to posterior
belly of
digastric muscle and
to the stylohyoid
muscle
Within parotid gland, nerve
terminates by splitting into 5
branches: Temporal, Zygomatic,
Buccal, Marginal
mandibular,Cervical

110. BRANCHES AND DISTRIBUTION
1)With in the facial canal
greater petrosal nerve
nerve to stapedius
The chorda tympani
2)As it exits from the stylomastoid foramen
posterior auricular
Digastric
Stylohyoid
3)Terminal branches within parotid
temporal
zygomatic
buccal
margina mandibular
cervical
4)Greater petrosal nerve

111. Motor Functions
 Branches of facial nerve are responsible for innervating
many of muscles of head and neck. All these muscles are
derivatives of second pharyngeal arch.
 The first motor branch arises within facial canal; nerve to
stapedius. nerve passes through pyramidal eminence to
supply stapedius muscle in middle ear
 Between stylomastoid foramen, and parotid gland, 3
more motor branches are given off:
 Posterior auricular nerve – Ascends in front of mastoid
process, and innervates intrinsic and extrinsic muscles of
outer ear. It also supplies occipital part of occipitofrontalis
muscle.

112.  Nerve to the posterior belly of
the digastric muscle – Innervates
a suprahyoid muscle of neck. It is responsible for
raising hyoid bone.
 Nerve to the stylohyoid muscle – Innervates
a suprahyoid muscle of neck. It is responsible for
raising hyoid bone.

113.  Within parotid gland, facial nerve terminates by
bifurcating into 5 motor branches. These innervate
muscles of facial expression:
 Temporal branch – Innervates frontalis, orbicularis oculi
and corrugator supercili
 Zygomatic branch – Innervates orbicularis oculi.
 Buccal branch – Innervates orbicularis oris, buccinator
and zygomaticus muscles.
 Marginal Mandibular branch– Innervates mentalis
muscle.
 Cervical branch – Innervates platysma

115. CLINICAL RELEVANCE: DAMAGE TO
THE FACIAL NERVE
 Facial nerve has a wide range of functions. Thus,
damage to nerve can produce a varied set of symptoms,
depending on the site of lesion.
 Bell’s palsy: sudden paralysis of nerve at stylomastoid
foramen. Results n asymmetry in corner of mouth,
inability to close eyes, disappearance of nasolabial fold,
loss of wrinkling of skin of forehead
 Chorda tympani –
reduced salivation and loss of taste on
ipsilateral 2/3 of the tongue

117.  Nerve to stapedius –
ipsilateral hyperacusis (hypersensitive to sound).
 Greater petrosal nerve –
ipsilateral reduced lacrimal fluid production.
 Facial nerve palsy of new born-
manipulation of babies head during delivery can
damage nerve

118.  Ramsay-hunt syndrome
involvement of geniculate ganglia by herpes zoster
-hyperacusis
-Loss of lacrimation
-Loss of sensationof taste in anterior two third of
tongue
-Bell’s palsy and lack of salivation
-Vesicles on auricle

119. VESTIBULO COCHLEAR NERVE
It is comprised of two parts –vestibular fibres
and cochlear fibres.
Both have a purely sensory function.

120. ANATOMIC COURSE
 The vestibular and cochlear portions of vestibulocochlear
nerve are functionally discrete, and so originate from
different nuclei in brain:
Vestibular component – arises from vestibular nuclei
complex in pons and medulla.
Cochlear component – arises from ventral and dorsal
cochlear nuclei, situated in inferior cerebellar peduncle.
 Both sets of fibres combine in the pons to form the
vestibulocochlear nerve. nerve emerges from the brain
at cerebellopontine angle and exits cranium via internal
acoustic meatus of temporal bone.

121.  Within distal aspect of internal acoustic meatus,
vestibulocochlear nerve splits, forming vestibular
nerve and cochlear nerve.
 vestibular nerve innervates vestibular system of
inner ear, which is responsible for detecting balance.
 The cochlear nerve travels to cochlea of inner ear,
forming spiral ganglia which serve sense of hearing.

123. Special Sensory Functions
Hearing
 The cochlea detects magnitude and frequency of sound
waves. inner hair cells of organ of Corti activate ion
channels in response to vibrations of basilar membrane.
Action potentials travel from spiral ganglia, which house
cell bodies of neurones of cochlear nerve.
 The magnitude of sound determines how much
membrane vibrates and thereby how often action
potentials are triggered. Louder sounds cause basilar
membrane to vibrate more, resulting in action potentials
being transmitted from spiral ganglia more often, and vice
versa. frequency of sound is coded by position of
activated inner hair cells along basilar membrane.

124. PATHWAY OF HEARING
-first neurons of pathway are located in the spiral ganglion.
They are bipolar.
Their peripheral processes innervate the spiral organ of
Corti,
while the central processes form the cochlear nerve.
This nerve terminates in the dorsal and ventral cochlear
nuclei
-The second neurons lie in the dorsal and ventral cochlear
nuclei.
Most of the axons arising in these nuclei cross to the
opposite side and terminate in the superior olivary nucleus
-The third neurons lie in the superior olivary nucleus.
Their axons from the lateral lemniscus and reach the
inferior colliculus

128. Equilibrium (Balance)
 The vestibular apparatus senses changes in the position
of the head in relation to gravity. vestibular hair cells are
located in the otolith organs (the utricule and saccule),
where they detect linear movements of the head, as well
as in the three semicircular canals, where they detect
rotational movements of the head. The cell bodies of the
vestibular nerve are located in the vestibular
ganglion which is housed in the outer part of the internal
acoustic meatus.
 Information about the position of the head is used
to coordinate balance and the vestibulo-ocular reflex.
The vestibulo-ocular reflex (also called the oculocephalic
reflex) allows images on the retina to be stabilised when
the head is turning by moving the eyes in the opposite
direction. It can be demonstrated by holding one finger
still at a comfortable distance in front of you and twisting
your head from side to side while staying focused on the
finger.

129. VESTIBULAR PATHWAY
-The vestibular receptors are the maculae of the saccule
and utricle and in the cristae of the ampullae of
semicircular ducts
-Fibers from cristae of anterior and lateral semicircular
canals and some fibers from the two macules lie in the
superior vestibular area of internal acoustic meatus
-Fibers of crista of the posterior semicircular canal lie in
foramen singulare
-Most of the fibers from the maculae of utricle and saccule
lie in inferior vestibular area

133. CLINICAL RELEVANCE:
BASILAR SKULL FRACTURE
 A basilar skull fracture is a fracture of the skull base,
usually resulting from major trauma. The
vestibulocochlear nerve can be damaged within the
internal acoustic meatus, producing symptoms of
vestibular and cochlear nerve damage.
 Patients may also exhibit signs related to the other
cranial nerves, bleeding from the ears and nose, and
cerebrospinal fluid leaking from the ears (CSF
otorrhoea) and nose (CSF rhinorrhoea).

134. CLINICAL RELEVANCE: VESTIBULAR
NEURITIS
VESTIBULAR NEURITIS
 inflammation of the vestibular branch of the
vestibulocochlear nerve.
 The aetiology of this condition is not fully understood, but
some cases are thought to be due to reactivation of the
herpes simplex virus.
 symptoms of vestibular nerve damage:
Vertigo – a false sensation that oneself or the
surroundings are spinning or moving.
Nystagmus – a repetitive, involuntary to-and-
fro oscillation of the eyes.
Loss of equilibrium (especially in low light).
Nausea and vomiting.
 The condition is usually self-resolving. Treatment is
symptomatic, usually in the form of anti-emetics or
vestibular suppressants

135. GLOSSOPHARYNGEAL NERVE

136.  third pharyngeal arch.
 Motor to stylopharyngeous
 Gustatory to posterior one third of tongue including
circumvalate papillae
 Sensory to pharynx, tonsil, soft palate , posterior one
third of tongue, carotid body and carotid sinus.
 Parasympathetic: Provides parasympathetic innervation
to parotid gland

137. ANATOMICAL COURSE
The glossopharyngeal nerve originates
in medulla oblongata of the brain.
It emerges from the anterior aspect of medulla, moving
laterally in the posterior cranial fossa.
The nerve leaves cranium via the jugular foramen.
At this point, tympanic nerve arises. It has a mixed
sensory and parasympathetic composition.

139.  Immediately outside jugular foramen lie two ganglia
 They are known as the superior and inferior (or
petrous) ganglia –
 They contain the cell bodies of the sensory fibres in
the glossopharyngeal nerve

140.  Now extracranial, the glossopharyngeal nerve
descends down the neck, anterolateral to the internal
carotid artery.
 At the inferior margin of the stylopharyngeus,
several branches arise to provide motor innervation to
the muscle.
 It also gives rise to the carotid sinus nerve, which
provides sensation to the carotid sinus and body.

141.  The nerve enters the pharynx by passing between
the superior and middle pharyngeal
constrictors. Within the pharynx, it terminates by
dividing into several branches – lingual, tonsil and
pharyngeal.

143. Sensory Functions
 The tympanic nerve - provide sensory innervation to
middle ear, internal surface of the tympanic
membrane and Eustachian tube.
 At the level of the stylopharyngeus, carotid sinus
nerve arises. It descends down the neck to innervates
both the carotid sinus and carotid body, providing
information regarding blood pressure and oxygenation
respectively.

144.  Pharyngeal branch – combines with fibres of the vagus
nerve to form the pharyngeal plexus. It innervates the
mucosa of the oropharynx
 Lingual branch – provides the posterior 1/3 of the
tongue with general and taste sensation
 Tonsillar branch – forms a network of nerves, known as
the tonsillar plexus, which innervates the palatine tonsils.

145. Special Sensory
 The glossopharyngeal nerve provides taste
sensation to the posterior 1/3 of the tongue, via its
lingual branch
Motor Functions
 The stylopharyngeus muscle of the pharynx is
innervated by the glossopharyngeal nerve.
 This muscle acts to shorten and widen the pharynx,
and elevate the larynx during swallowing

146. CLINICAL RELEVANCE
 Lesions of this nerve cause
a)Absence of secretions of parotid gland
b)Absence of taste from posterior one third of the tongue
and circumvallate papillae
c)Loss of pain sensation from tongue tonsil pharynx and
soft palate
d)Gag reflex absent

147. CLINICAL RELEVANCE – GAG
REFLEX
 The glossopharyngeal nerve supplies sensory
innervation to the oropharynx, and thus carries
the afferent information for the gag reflex. When a
foreign object touches the back of the mouth, this
stimulates CNIX, beginning the reflex. The efferent
nerve in this process is the vagus nerve, CNX.
 An absent gag reflex signifies damage to the
glossopharyngeal nerve

148. VAGUS NERVE

149.  Vague course
 It is a functionally diverse nerve, offering many different
modalities of innervation.
 Due to its widespread functions, pathology of the vagus
nerve is implicated in a vast variety of clinical cases.
 The vagus nerve is associated with the derivatives of the
fourth pharyngeal arch.

150.  Sensory: Innervates the skin of the external acoustic
meatus and the internal surfaces of the laryngopharynx
and larynx. Provides visceral sensation to the heart and
abdominal viscera.
 Special Sensory: Provides taste sensation to the
epiglottis and root of the tongue.
 Motor: Provides motor innervation to the majority of the
muscles of the pharynx, soft palate and larynx.
 Parasympathetic: Innervates the smooth muscle of the
trachea, bronchi and gastro-intestinal tract and regulates
heart rhythm.

151. ANATOMICAL COURSE
 The vagus nerve has the longest course of all the cranial
nerves, extending from the head to the abdomen. Its
name is derived from the Latin ‘vagary’ – meaning
wandering. It is sometimes referred to as the wandering
nerve

152. The vagus nerve
originates from the
medulla of the
brainstem. It exits the
cranium via thejugular
foramen, with the
glossopharyngeal and
accessory nerves
Within the cranium,
the auricular
branch arises.
This supplies
sensation to the
posterior part of the
external auditory and
canal external ear.

153.  In the Neck
In the neck, the vagus nerve passes into the carotid
sheath, travelling inferiorly with the internal jugular vein
and common carotid artery. At the base of the neck, the
right and left nerves have differing pathways:

155. Relation of cranial nerves IX X XI XII to carotid arteries and internal
jugular vein

156. In the neck
Right vagus enters by crossing
the first part of subclavian artery
and then inclining medially behind
the brachiocephalic vessels to
reach the right side of the trachea.
The left vagus enters y passing
between the left common carotid
and left subclavian arteries,
behind the internal jugular and the
brachiocephalic veins

158.  Several branches arise in the neck:
Pharyngeal branches –
Provides motor innervation to the majority of the
muscles of the pharynx and soft palate.
Superior laryngeal nerve –
Splits into internal and external branches. The external
laryngeal nerve innervates the cricothyroid muscle of the
larynx. The internal laryngeal provides sensory
innervation to the laryngopharynx and superior part of the
larynx.
Right Recurrent laryngeal nerve –
Hooks underneath the right subclavian artery, then
ascends towards to the larynx. It innervates the majority
of the intrinsic muscles of the larynx

160. In the thorax
 The right vagus nerve forms the posterior vagal trunk, and
the left forms the anterior vagal trunk.
 Branches from the vagal trunks contribute to the formation of
the oesophageal plexus, which innervates the smooth
muscle of the oesophagus.
 Two other branches arise in the thorax:
Left recurrent laryngeal nerve –
it hooks under the arch of the aorta, ascending to innervate
the majority of the intrinsic muscles of the larynx.
Cardiac branches –
these innervate regulate heart rate and provide visceral
sensation to the organ.
 The vagal trunks enter the abdomen via the oesophageal
hiatus, an opening in the diaphragm.

162. In the abdomen
In the abdomen, the vagal trunks terminate by dividing
into branches that supply the oesophagus, stomach and
the small and large bowel (up to the splenic flexure).

163. Sensory Functions
 Laryngopharynx – via the internal laryngeal nerve.
 Superior aspect of larynx (above vocal folds) – via the
internal laryngeal nerve.
 Heart – via cardiac branches of the vagus nerve.
 Gastro-intestinal tract (up to the splenic flexure) – via the
terminal branches of the vagus nerve.
Special Sensory Functions
 The vagus nerve has a minor role in taste sensation.
It carries afferent fibres from the root of the
tongue and epiglottis.

164. Motor functions
 The vagus nerve innervates the majority of the muscles
associated with the pharynx and larynx. These muscles are
responsible for the initiation of deglutition
Muscles of the Pharynx
 Most of the muscles of the pharynx are innervated by
the pharyngeal branches of the vagus nerve:
 Superior, middle and inferior pharyngeal constrictor muscles
 Palatopharyngeus
 Salpingopharyngeus
 An additional muscle of the pharynx, the stylopharyngeus,
is innervated by the glossopharyngeal nerve.

165. muscles of the Larynx
 Innervation to the intrinsic muscles of the larynx is
achieved via the recurrent laryngeal nerve and external
branch of the superior laryngeal nerve.
External laryngeal nerve:
 Cricothyroid
Other Muscles
 In addition to the pharynx and larynx, the vagus nerve
also innervates the palatoglossus of the tongue, and the
majority of the muscles of the soft palate.

166. Parasympathetic Functions
 In the thorax and abdomen, the vagus nerve is the
main parasympathetic outflow to the heart and gastro-
intestinal organs.
CLINICAL RELEVANCE
Vasovagal syncope can ensue during a period of emotional
stress for example causing a sudden drop in blood pressure
and heart rate. Further to this a carotid massage can
compress the carotid sinus leading to the perception of a high
blood pressure. This will cause CN X to increase its firing
leading to a decreased activity of the SA node and AV node.
Overall a decreased rate and strength of contraction will ensue
and the person may experience syncope.
The CN IX is sensory to the oropharynx and laryngopharynx
with CN X being the motor efferents involved in the Gag reflex
therefore a lesion in this area will cause a loss of the Gag
reflex.

167. SPINAL ACESSORY NERVE

168.  Purely somatic motor function, innervating the
sternocleidomastoid and trapezius muscles
 2 roots
a)Cranial:Acessory to the vagus and is distributed through
the branches of latter
b)Spinal:More independent course

169. CRANIAL PART
 The cranial portion is much smaller, and arises from the
lateral aspect of the medulla oblongata.
 It leaves the cranium via the jugular foramen, where it
briefly contacts the spinal part of the accessory nerve.
 Immediately after leaving the skull, cranial part
combines with the vagus nerve (CN X) at the inferior
ganglion of vagus nerve .
 The fibres from the cranial part are then distributed
through the vagus nerve. For this reason, the cranial
part of the accessory nerve is considered as part of the
vagus nerve.

171. SPINAL PART
 The spinal portion arises from neurones of the upper
spinal cord, specifically C1-C5/C6 spinal nerve roots.
These fibres coalesce to form the spinal part of the
accessory nerve, which then runs superiorly to enter the
cranial cavity via the foramen magnum.
 The nerve traverses the posterior cranial fossa to reach
the jugular foramen. It briefly meets the cranial portion of
the accessory nerve, before exiting the skull (along with
the glossopharyngeal and vagus nerves).
 Outside the cranium, the spinal part descends along
the internal carotid artery to reach the
sternocleidomastoid muscle, which it innervates. It then
moves across the posterior triangle of the neck to supply
motor fibres to the trapezius

173. MOTOR FUNCTION
The spinal accessory nerve innervates two muscles –
sternocleidomastoid
trapezius
CLINICAL RELEVANCE
EXAMINATION OF THE ACCESSORY NERVE
 The nerve is examined by asking the patient to rotate their
head and shrug their shoulders, both normally and against
resistance. Simply observing the patient may also reveal
signs of muscle wasting in the sternocleidomastoid and
trapezius in cases of long-standing nerve damage.
 By asking the patient to turn the chin to the opposite
side(sternocleidomastoid) against resistance and again
comparing the power on the two side .

174. Shrugging shoulders against resistance.
left side is weak.
Rotation of head to right side against
resistance to see the action of left
sternocleidomastoid

175. PALSY OF THE ACCESSORY NERVE
 The most common cause of accessory nerve damage
is iatrogenic (i.e. due to a medical procedure). In particular,
operations such as cervical lymph node biopsy can cause
trauma to the nerve.
Drooping of the right shoulder
due to paralysis of right trapezius

176. Hypoglossal nerve
 Name derived from ancient greek,
‘hypo‘-under,
‘glossal‘-tongue.
 The nerve has a purely somatic motor function,
innervating the majority of the muscles of the tongue.

177. nerve arises
from
the hypogloss
al nucleus in
the medulla
oblongata of
the brain. It
then passes
laterally across
the posterior
cranial fossa,
within
the subarachn
oid space. The
nerve exits the
cranium via
the hypogloss
al canal.
Now
extracranial,
the nerve
receives a
branch of the
cervical
plexus that
conducts
fibres
from C1/C2
spinal nerve
roots. These
fibres do not
combine with
the
hypoglossal
nerve – they
merely travel
It then passes
inferiorly to the
angle of
the mandible,
crossing the
internal and
external carotid
arteries, and
moving in an
anterior
direction to
enter the
tongue.

179. MOTOR FUNCTION
 Nerve is responsible for motor innervation of majority of the
muscles of the tongue (except for palatoglossus).
 These muscles can be subdivided into two groups:
i) Extrinsic muscles
Genioglossus (makes up the bulk of the tongue)
Hyoglossus
Styloglossus
Palatoglossus (innervated by vagus nerve)
ii) Intrinsic muscles
Superior longitudinal
Inferior longitudinal
Transverse
Vertical
Together, these muscles are responsible for all movements of the
tongue

181. ROLE OF THE C1/C2 ROOTS
 The C1/C2 roots that travel with the hypoglossal nerve
also have a motor function.
 They branch off to innervate
geniohyoid (elevates the hyoid bone)
thryohyoid (depresses the hyoid bone).
 Another branch containing C1/C2 fibres descends to
supply the ansa cervicalis
 From the ansa cervicalis, nerves arise to innervate
omohyoid
sternohyoid
sternthyroid muscles.
 These muscles all act to depress the hyoid bone.

183. CLINICAL RELEVANCE-
EXAMINATION OF THE HYPOGLOSSAL
NERVE
 Examined by asking the patient to protrude their tongue.
Other movements such as asking the patient to push
their tongue against their cheek and feeling for the
pressure on the opposite side of the cheek may also be
used if damage is suspected.

184. PALSY OF THE HYPOGLOSSAL NERVE
 Damage to the hypoglossal nerve is a relatively
uncommon cranial nerve palsy.
 Possible causes include tumours and penetrating
traumatic injuries.
 Patients will present with deviation of the tongue towards
the damaged side on protrusion, as well as possible
muscle wasting and fasciculations (twitching of isolated
groups of muscle fibres) on the affected side.

186. Conclusion

187. Reference
Clinical antomy of cranial nerves- PAUL REA
Human embryology- HAMILTON,BOYD and
MOSSMAN
Human embryology and developmental biology
- BRUCE M CHARLSON
BD CHAURASIA - Human anatomy
GRAYS ANATOMY-Anatomy basics and clinical practice
Atlas of human anatomy-FRANK H NETTER