Cranial nerves /certified fixed orthodontic courses by Indian dental academy

CRANIAL NERVES

INDIAN DENTAL ACADEMY
Leader in continuing dental education
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INTRODUCTION
• Nerves are a collection of axons contained within the
peripheral nervous system whereas tracts are a
collection of axons in the central nervous system (i.e. the
brain and spinal cord). Therefore, when we talk about
the cranial nerves we are really referring to part of the
peripheral nervous system.
• What makes the cranial nerves so special, after all we
have hundreds of nerves throughout the body? The
answer is that the cranial nerves are nerves that come
directly off of the brain


INTRODUCTION
• Modality is unit of the nervous system that
performs a certain type of action: sensation,
movement, constriction, etc.
• There are two general modalities in the
peripheral nervous system: motor (efferent) and
sensory (afferent).
• Efferent impulses
• Afferent impulses


INTRODUCTION
• There are 12 pairs of cranial nerves that
supply structures in the head, neck, thorax
and abdomen.
• A cranial nerve can be made up of a
mixture of functions which are called
modalities or may be made up of a single
modality.
• A modality is sensory, motor, special
sensory, etc.

EMBRYOLOGY
• INTRODUCTION:
• The Neural tube and its Subdivisions:
- Apart from its blood vessels and some
neuroglial elements, the whole of the nervous
system is derived from Ectoderm.
- The part of the ectoderm that is destined to
give origin to the brain and spinal cord, can be
distinguished while the embryo is still in the from
of a three-layered embryonic disc.

- It soon becomes thickened to form the neural
plate.
- The neural plate becomes depressed along
the midline as as result of which the neural
groove is formed.
- This groove becomes progressively deeper, at
the same time the two edges of the neural plate
come nearer each other, and eventually fuse,
thus converting the neural groove into the
neural tube.


• THE NEURAL CREST:
- At the time when the neural plate is being formed,
some cells at the junction between the neural plate
and the rest of the ectoderm become specialized to
form the primordia of the neural crest.
- The spinal cord is developed from the caudal
cylindrical part of the neural tube.
- The medulla oblongata develops from the
Myelencephalon.
- The pons arises from the ventral part of the
Metencephalon
- The Mid brain is developed from the Mesencephalon

- The cerebellum develops from the
dorsolateral part of the alar lamina of the
Metencephalon.
- The Cerebral hemisphere is a derivative of the
Prosencephalon.
- The Thalamus and Hypothalamus develop
from the Diencephalon.
- The Corpus striatum is a derivative of the
Telencephalon.
- The Cerebral cortex is fromed by migration of
the cells from the mantle layer into the
overlying marginal layer.

NAMES OF CRANIAL NERVES
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Ⅰ Olfactory nerve
Ⅱ Optic nerve
Ⅲ Oculomotor nerve
Ⅳ Trochlear nerve
Ⅴ Trigeminal nerve
Ⅵ Abducent nerve
Ⅶ Facial nerve
Ⅷ Vestibulocochlear
nerve
Ⅸ Glossopharyngeal
nerve
Ⅹ Vagus nerve
Ⅺ Accessory nerve
Ⅻ Hypoglossal nerve

FUNCTIONAL COMPONENTS
• GSE -- motor to skeletal muscles
GVE -- motor to heart muscle, smooth muscle, glands. In
the cranial nerves, these impulses are part of the
parasympathetic nervous system.
SVE -- motor to skeletal muscles that develop in
branchial arches of the embryo (pharynx, larynx, middle
ear)
GSA -- sensations of touch, pain, temperature
SSA -- special sense from organs developing in
ectoderm of embryo (vision, hearing)
GVA -- sensory from sensory organs (heart, intestine)
SVA -- special sense from organs developing in
association of gastrointestinal tract (smell, taste)


CLASSIFICATION OF CRANIAL NERVES
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Sensory cranial nerves: contain only afferent (sensory) fibers
– Ⅰ Olfactory nerve,
– Ⅱ Optic nerve,
– Ⅷ Vestibulocochlear nerve.
Motor cranial nerves: contain only efferent (motor) fibers
– Ⅲ Oculomotor nerve,
– Ⅳ Trochlear nerve,
– Ⅵ Abducent nerve,
– Ⅺ Accessory nerve,
– Ⅻ Hypoglossal nerve.
Mixed nerves: contain both sensory and motor fibers--– Ⅴ Trigeminal nerve,
– Ⅶ Facial nerve,
– Ⅸ Glossopharyngeal nerve,
– Ⅹ Vagus nerve.


ORIGIN


CONTENTS
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Type
Origin
Innervation
Course
Applied Anatomy

OLFACTORY NERVE


OLFACTORY NERVE
• It is the first cranial nerve
and nerve of smell and
form first order neuron of
olfactory pathway.
• Type → Special Sensory
type.
• Origin → From olfactory
epithelium in the olfactory
region of nasal cavity
(superior nasal concha
and opposed part of
nasal septum).

• Course → After origin they pass through the
cribriform plate of ethmoid bone and within the
cranial cavity they end.

• Innervation → Nasal Mucous Membranes.

• Enter → Cribriform plate of the ethmoid bone.

• Applied anatomy →
 In case of fracture of anterior cranial fossa
olfactory nerves may be separated from
olfactory bulb and results in loss of smell
(Anosmia).
 It may tear the meningeal sheaths, so leakage
of CSF from nose.
 Infection from nose may spread through the
meningeal sheaths to brain and intracranial
complication and Meningitis and encephalitis
may occur.

EXAMINATION OF THE CRANIAL
NERVES
• a) Introduce yourself, obtain consent,
wash your hands.
• b) Position patient (they should be sitting
in a chair or on the edge of a bed).
• c) General inspection.


OLFACTORY NERVE
• Ask “Have you noticed any change in your
sense of smell or taste recently?”
• If yes, check that the problem is not due to a
cold/blocked nose and say “I would like to
formally examine the sense of smell”. This
involves the use of bottles containing standard
smells (rarely used) or the use of a substance
with a strong aroma eg. coffee. Remember to
test each nostril separately.

OPTIC NERVE


OPTIC NERVE
• It is the second
cranial nerve and
is nerve of vision.
• Type → Special
Sensory Type


• Origin → Its fibres origin from Ganglionic layer of
retina and stratum opticum.
• Innervation → Optic Canals.
• Course → After emerging out of the eyeball it
passes through the orbit for a short course and
enters the cranial cavity by passing through the
optic foramen. In the cranial cavity on the superior
surface of body of sphenoid bone it ends.
• Intra cranial part → It runs backwards and
medially from optic canal to optic chiasma.

• Applied anatomy → Lesions of different parts of the
pathways and effects
 Retina – Scotoma (Blind spots in certain parts).
 Optic nerve – Due to injury and effect is blindness.
 Optic chiasma –
a) Central part – Bitemporal hemianopia.
b) Peripheral part (both side) – Binasal hemianopia.
[ Hemianopia is loss of vision in one half of field of vision.]

CRANIAL NERVE FUNCTION & MUSCLE INNERVATION
RELATIVE TO EYE MOVEMENT
Superior rectus
CN III

Lateral rectus
CN VI

Inferior rectus
CN III

Inferior oblique
CN III

Medial rectus
CN III


Superior oblique
CN IV

OPTIC EXAMINATION
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Remember APAFF:
Acuity
Pupils
Accommodation
Fields
Fundoscopy


Acuity
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Ask “Do you usually wear glasses/contact lenses?” If
yes, ask patient to put them on. Use a pocket Snellen
chart. “Cover your left eye with your left hand and
read down the chart from the top”. Repeat for right
eye. Record visual acuity. If no Snellen chart
available, test using a magazine/name badge and say
“I would like to formally assess acuity using a Snellen
chart at 6m”.
If unable to see letters, check if able to: count fingers,
detect hand movement, detect light.


Pupils
• PERLA – are the Pupils Equal and Reactive to
Light and Accommodation?
• Inspect size and symmetry of pupils. Tell the
patient that you are going to shine a light in their
eyes. Shine a pen torch twice into each eye
checking first for a direct and then for a
consensual response (both pupils should
constrict in response to a light being shone in
either one of them). Dimming background light
makes this process easier.

Accommodation
• Ask the patient to look at a point on the far
side of the room. Then ask them to look
at a point about 15cm from their face. The
pupils should constrict as the patient
focuses on the near object.


Fields
• Tested by confrontation. Sit in front of, and at the same
level as, the patient, about 1m apart. “Cover your right
eye with your right hand please and look straight into my
eye” (you should cover your left eye with your left hand
at the same time). Bring a target (ideally a red hat pin,
otherwise the wiggling end of your finger) in diagonally
from above and below on each side (you will need to
swap hands halfway through), making sure that the
target is equidistant between the two of you. Ask the
patient when they first see the target. Repeat for the
other eye. Compare your fields with those of the patient.


Fundoscopy
• Say “I would also like to examine the fundi
with an ophthalmoscope”.


OCCULOMOTOR NERVE
• It is the third nerve
supplying all the
muscles of the eye
ball except Lateral
rectus and Superior
oblique and also
supplies sphincter
pupillae and ciliaris
muscle.
• Type → Motor

• Origin → ORIGIN (Deep origin or nucleus of
origin) : Nucleus of the third nerve lies in the grey
matter of upper part of floor of cerebral aqueduct of
midbrain at the level of superior colliculi .

• Nucleus of third nerve: Segmental and
consists of following components with function.
• Enter → Superior Orbital Fissure.
• Innervation → LPS,SR,IR,MR & IO.
• Course → Intra neural part & Extra neural part

• I) Intracranial part: From the nucleus of origin the
fibres pass through the tegmentum. Red nucleus
and medial part of substantia nigra in a curved
manner and finally emerges out of the brain from
the medial side of the crus cerbri through
oculomotor sulcus.
• Superficial origin: From the oculomotor sulcus on
the medial side of crus cerebri.
• II) Extracranial part: The fibre of the oculomotor
nerve after emerging out of the brain through
oculomotor sulcus leaves the pial sheath and runs
in the subarachnoid space.

• Applied anatomy →
 Complete optholmoplegia : loss of function of all three of these
nerves, and can result from cavernous sinus thrombosis, superior
orbital fissure fracture, or elevated ICP.
 Traumatic mydriasis : damager to the third nerve _ dilatation and
non-reactivity of the pupil.
 Ptosis : Drooping of upper eyelid due to paralysis of levator
palpebrae.
 Lateral strabismus (squint) : due to unopposed action of lateral
rectus.
 Dilation of pupil : due to paralysis of sphincter pupillae and ciliaris
muscle slight prominence of eyeball owing to most of the muscles of
eyeball being relaxed.
 The third nerve is usually affected due to syphilitic periarteritis of
posterior cerebral and superior cerebellar arteries as the nerve
passes between them.

TROCHLEAR NERVE


TROCHLEAR NERVE
• It is the fourth cranial
nerve which supplies
superior oblique muscle
of eyeball.
• Type → Motor
• Origin →Deep or
Nucleus of origin :
Nucleus of the trochlear
nerve lies in the grey
matter of lower part of the
floor of cerebral aqueduct
at the level of inferior
colliculi.

• Course → Intraneural (part within the brain) –From the
nucleus of origin the nerve runs downwards and laterally
in the tegmentum and then turns backwards around the
central grey matter towards the dorsal aspect of the brain
stem. Here the two nerves cross each other before
emergence.
• Superficial origin: It emerges out below inferior colliculus
and on surface of superior medullary velum ends on each
side of frenulum veli.
• Intracranial part: The trochlear nucleus gives rise to
nerves that cross (decussate) to the other side of the
brainstem just prior to exiting the brainstem. The trochlear
nerve fibers curve forward and enter the duramater at the
angle between the free and attached border of the
tentorium cerebelli. The nerve travels in the lateral wall of
the cavernous sinus and then enters the orbit via the
superior orbital fissure.

• Innervation → SOM

• Applied anatomy :
 If the nerve is injured, downward and lateral movement of
eyeball will not be possible and no difficulty so long the
patient looks above the horizontal level.
 Double vision will occur if he looks downward and the
patient has a pathetic look and so this nerve is known as
pathetic nerve.


TRIGEMINAL NERVE


TRIGEMINAL NERVE
• Attached to the side of
pons, very large.
Sensory from muscles of
mastication, skin of face
and scalp, mucous
membranes of mouth and
nasal cavity, cornea of
eye, teeth, and
duramater. Motor to
muscles of mastication.


TRIGEMINAL NERVE
• It is the fifth cranial nerve and largest of all
cranial nerves.
• Type → Mixed so both Motor & Sensory.


• Origin → Deep origin or Nucleus of origin
• I. Sensory nucleus (Principal): Situated within the pons lateral to
the motor nucleus of nerve. It receives sensory fibres for touch
sensation.
• II. Spinal nucleus of trigeminal nerve: An elongated nucleus
extending from the sensory nucleus, cranially to second or third
cervical spinal segments caudally. It receives pain and
temperature from trigeminal area.
• III. Mesencephalic nucleus: Situated in the central grey matter of
mid brain on either side of cerebral aqueduct. It receives
proprioceptive sensations of the fifth nerve.
• IV. Motor nucleus: Situated within the pons, medial to sensory
nucleus and the fibres from it form the motor root of the nerve.
This nucleus represents the special visceral afferent column.

• Superficial origin: Two roots: Motor and
sensory emerge from the ventral aspect of the
pons. Sensory root larger and motor root
smaller and motor root lies ventrimedial to
sensory root.
• The sensory root passes forward from the
posterior cranial fossa and joins the concave
posterior margin of trigeminal ganglion.
• The motor root passes forward and then
passes below the sensory root and trigeminal
ganglion in the trigeminal cave and finally joins
with the sensory part of mandibular nerve in the
foramen ovale and from trunk of mandibular
nerve.

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Branches
Ophthalmic Nerve (V1) → Purely Sensory Nerve.
Maxillary Nerve (V2) → Sensory.
Mandibular Nerve (V3) → Mixed and consisting of two
roots.

• 1.OPTHALMIC NERVE:
- It is one of the divisions of trigeminal nerve.
- It is purely a sensory nerve.
- Arises from the convex anterior margin of trigeminal
ganglion.
- After origin it lies on the lateral wall of cavernous
sinus below 4th cranial nerve and above maxillary
division.
- In the anterior part of cavernous sinus it terminates
by dividing into a) Frontal, b) Lacrimal, c) Nasociliary.

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FRONTAL NERVE:
Largest branch of ophthalmic nerve.
It is a sensory nerve.
It enters the orbit through lateral part of sof outside the annulus tendinous
communis (ring) lateral to trochlear nerve.
It terminates in the midway between base and apex of the orbit by dividing
into two branches.
A. supratrochlear.
B. supraorbital.
LACRIMAL NERVE:
Smallest of the branches of ophthalmic nerve and sensory nerve.
Receives few filaments from trochlear nerve and these filaments are
those which pass from ophthalmic to trochlear nerve previously.
It passes to orbit through lateral compartment of superior orbital fissure
outside annulus tendinous ring and lateral to frontal nerve.
It passes above lateral rectus accompanied by lacrimal artery and
receives a twig from zygomatico-temporal branch which carries post
ganglionic secretomotor fibres of lacrimal gland.

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NASOCILIARY NERVE:
1) It is a sensory nerve and one of the three branches of ophthalmic
nerve.
2) Origin: It arises from the ophthalmic nerve in the anterior part of
cavernous sinus.
3) It enters the orbit by passing through the middle compartment of
superior orbital fissure within the annulus tendinous communis and
then the two heads of lateral rectus muscle.
4) Ultimately it passes through anterior ethmoidal foramen and terminates
by continuing as anterior ethmoidal nerve.
5) Branches1)Branches of communication: Sympathetic plexus, 3rd nerve, ciliary
ganglion.
2)Branches of distributioni. Long ciliary branches.
ii. Posterior ethmoidal.
iii. Infratrochlear.
iv. Anterior ethmoidal
a) Internal nasal branch.
b) External nasal branch.

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2. MAXILLARY NERVE:
It is the intermediate division of trigeminal nerve.
Origin: from the convex aspect of trigeminal ganglion.
Course: After origin it runs forwards along the lower part of lateral wall of
cavernous sinus below the ophthalmic nerve.
Then it leaves the skull by passing through foramen rotundum and
enters into the pterygopalatine fossa. From there it inclines to the posterior
surface of maxilla and enters the orbit through inferior orbital fissure. It is then
named infraorbital nerve It passes through infraorbital groove and canal on the
floor of the orbit.
Branches:
1) Within cranium: Meningeal. It supplies duramater of middle and partly in the
anterior cranial fossa.
2) In the pterygopalatine fossa:
1) Ganglionic:
2) Zygomatic:
a. zygomaticotemporal
b. zygomaticofacial.
3) Posterior superior alveolar.
3) In the infraorbital canal:
i. Middle superior alveolar.
ii. Anterior superior alveolar.
4) In the face:
1. Palpebral.
2. Nasal.
3. Superior labial.

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3. MANDIBULAR NERVE:
It is the largest division of trigeminal nerve.
Origin: Larger sensory root arises from convex aspect of
trigeminal ganglion and smaller motor root from motor
nucleus of trigeminal nerve in the pons.
Course: The united trunk enters the infratemporal fossa by
passing through foramen ovale and lies in between tensor
veli palate-medially and lateral pterygoid laterally.
Branches:
1) From the trunk, i.e. before division:
i) Nervous spinous or meningeal branch
ii) Nerve to medial pterygoid.
2) From anterior divisions:
Motor branches:
i) Deep temporal
ii) Nerve to lateral pterygoid
iii) Massetric
Sensory branch: Buccal nerve and skin

3) Posterior division:
I) Auriculotemporal:
a) Branches of communicationi) With otic ganglion and receives post Ganglionic
secretomotor fibres for the parotid gland.
ii) With seventh nerve.
b) Branches of distributioni) Anterior auricular - to pinna.
ii) External acoustic branch.
iii) Articular branches to temporomandibular joint.
iv) Parotid branches.
v) Superficial temporal branches.

II) Lingual nerve: it is a sensory nerve for mucous
membrane to anterior 2/3rd of tongue, floor of the mouth
and gum.
ORIGIN: from the posterior trunk of mandibular nerve in
the infratemporal fossa.
COURSE: after origin it passes between tensor palate and
lateral pterygoid and in this part chorda tympani nerve
joins it and also a branch from inferior alveolar nerve.
Distribution:
branches supply:
Mucous membrane of floor of mouth, Lingual surface of
gum,Mucous membrane of anterior 2/3rd of tongue
except vallate papilla, It also carries post Ganglionic
fibres from submandibular ganglion for sublingual
salivary and anterior lingual gland.

• Inferior alveolar nerve: It is the branch of
posterior trunk of mandibular nerve.
• Course: it runs downward deep to lateral
pterygoid and passes between
sphenomandibular ligament and ramus of
mandible upto mandibular foramen and enters
the mandibular canal and runs below the teeth
as far as mental foramen and terminates by
dividing into mental and incisive branch.
• Branches:
1) Nerve to myolohyoid
2) Mental
3) Incisive branch
4) Dental branch

• Applied anatomy:
 The sensory root of this nerve is divided into
three divisions, each division may be tested by
light touch or pinprick on the skin overlying its
respective area of distribution.
 The motor root of trigeminal supplies the
muscles of mastication and can be tested by
palpating the temporalis and masseter during
clenching movements.


• Applied anatomy:
 Lesion of whole of trigeminal nerve,
1) Anesthesia of the corresponding anterior half of
scalp, face(except the area at the angle of mouth,
because of supply by great auricular), cornea,
conjunctiva, mucous membrane of nose, mouth,
anterior 2/3rd of tongue.
2) Paralysis and atrophy of muscles supplied by the
nerve and so when patient tries to open the mouth
the mandible will thrust to the paralysed side.
 Lesions of any divisions of nerve.
 Lesion of lingual nerve below the point of joining of
chorda tympani .
 Pain or neuralgia is of very common.
 In case of frontal or ethmoidal sinusitis or glaucoma
severe supraorbital pain occurs. It is also a case of
referred pain. www.indiandentalacademy.com

 Trigeminal neuralgia (TN) : is a disorder of
unilateral (usually right-sided) facial pain. While the
exact cause is unknown, it is thought that TN results
from irritation of the trigeminal nerve. This irritation
results from damage due either to changes in the
blood vessels or the presence of a tumor or other
lesions that cause compression of the nerve.
 The pain quality is usually sharp, stabbing, lancinating
(cutting or tearing), and burning. It may have an
"electric shock"-like character.
 In some individuals the attacks may be initiated by
non-painful physical stimulation of specific areas
(trigger points or zones) that are located on the same
side of the face as the pain.

ABDUCENT NERVE


ABDUCENT NERVE
• It is the sixth cranial nerve
which supplies lateral rectus
muscle.
• Type → Motor nerve.
• Origin → The fibres arise
from a small nucleus
situated in the dorsal aspect
of the pons in the floor of
the fourth ventricle close to
the median plane and
beneath the facial colliculus.

• Course → The abducent nerve after leaving the brain stem runs
upwards laterally and forwards through cisterna pontis.As it proceeds
forwards it will be crossed by anterior inferior cerebellar artery
ventrally and then loses its dural sheath at the lateral side of dorsal
sellae. Then it bends sharply forwards at the apex of petrous part of
temporal bone to the lateral margin of dorsum sellae. After that enters
into orbital cavity through middle part of superior orbital fissure within
annulous tendinous communis. Finally it terminates in the orbit.
• Enter → Superior Orbital Fissure.
• APPLIED ANATOMY:
 It is liable to be damaged during fracture of skull. When intracranial
pressure increases, pons is pushed backwards and downwards and
this nerve may get stretched and may lose its function.
 Effects of paralysis:
– Convergent squint due to unopposed action of medial rectus.
– Often diplopia with convergent squint will be present.

References
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Gray’s Anatomy 2nd edition.
B D Chaurasia 3rd Vol 4th edition.
Human Anatomy Chakraborthy.
Hutchinson’s clinical manual.


thank you


Facial Nerve


FACIAL
• Origin → Lateral
Surface of the
Brainstem.
• Course
• Enter


Vestibulocochlear Nerve


VESTIBULOCOCHLEAR
• Origin → Lateral
Surface of the
Brainstem.
• Course → Pons &
Medulla.
• Enter →


Glossopharyngeal Nerve


GLOSSOPHARYNGEAL
• Origin
• Course
• Enter


Vagus Nerve


VAGUS
• Origin
• Course
• Enter


Spinal Accessory Nerve


SPINAL ACCESSORY
• Origin
• Course
• Enter


Hypoglossal Nerve


HYPOGLOSSAL
• Origin
• Course
• Enter


Under the Guidance of
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Prof. L. Krishna Prasad
Prof. Srinivas Chakravarthy
Dr. Neelima
Dr. M. Sridhar
Dr. Raja Subhash
Dr. Suprakash
Dr. Giridhar Kumar
Dr. Sumanth Krishna

Some Facts About The Cranial
Nerves
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Which cranial nerve is the largest?
CN V (Trigeminal)
Which cranial nerve is the only one that exits the "posterior" side of the brainstem?
CN IV (Trochlear)
How many cranial nerves are responsible for eye movements?
Three: CN III (Oculomotor), IV (Trochlear), and VI (Abducens).
What does "abducens" refer to?
The abducens nerve carries motor impulses to the lateral rectus eye muscle which moves
the eye laterally causing abduction of the eye.
Which cranial nerves carry gustatory (taste) information?
CN VII (Facial), CN IX (Glossopharyngeal) and CN X (Vagus).
Which cranial nerve is the longest?
CN X (Vagus) which reaches from the medulla to the digestive and urinary organs.
What two cranial nerves carry sensory information about blood pressure to the
brain?
CN IX (Glossopharyngeal) and CN X (Vagus).
Which cranial nerve is responsible for pupillary constriction?
CN III (Oculomotor).


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