Cranial Nerve I: Olfactory
• It is the first cranial nerve and nerve of
smell and form first order neuron of
• Type → Special Sensory type.
• Origin → From olfactory epithelium in the
olfactory region of nasal cavity (superior
nasal concha and opposed part of nasal
• Course → Fibers run through the olfactory bulb
( mitral cells)olfactory tract and terminate in the
primary olfactory cortex
• Innervation → Nasal Mucous Membranes.
• Enter → Cribriform plate of the ethmoid bone.
• 3000 different odours
• I sensation to appear in vertebrate
• II order neuron ( mitral cells) reaches
cortex directly without involvement of
• Ipsilateral - no significant decussation
• Anosmia (Olfactory anaesthesia)
• Head Injuries -–> CSF Rhinorrhoea.
• CVA -> Effusion of blood into base of frontal lobe
• Tumours of the Frontal lobe, or those arising near the
• Infections –tuberculous meningitis infections like common
cold, Viral Hepatitis, syphilis, osteomyelitis of frontal or
• Unilateral Anosmia may be of diagnostic significance in
localizing brain lessons.
• Reduction – hyposmia – local abn of nose
• Distortion of smell – parosmia – Head
injury or local abnormalities of nose
• Increased smell – hyperosmia – In neurotic
• Olfactory hallucinations & delusions –
epilepsy, migraine, psychiatric patients.
Cranial Nerve II - Optic
• Part of the CNS as it is derived from an
outpouching of the diencephalon during
• The fibres are covered with myelin produced by
oligodendrocytes rather than the Schwann cells of
the peripheral nervous system and are encased
within the meninges
• Therefore peripheral neuropathies like GuillainBarré syndrome do not affect the optic N
• ORIGIN: Arises from the retina of the eye.
• COURSE: Optic nerves pass thru’ the optic canals
and converge at the optic chiasma
• They continue as optic tract to the thalamus
where they synapse
• From there, the optic radiation fibers run to the
visual cortex of occipital lobe.
Right-sided circumferential blindness due to retrobulbar neuritis.
Total blindness of the right eye due to lesion of right optic nerve.
Right nasal hemianopia due to partial lesion of right optic chiasm.
Bitemporal hemianopia due to a complete lesion of the optic chiasm.
Left temporal and right nasal hemianopias due to a lesion of the right
optic tract (homonymous hemianopia)
Left temporal and right nasal hemianopia due to a lesion of the right
Left temporal and right nasal hemianopia due to a lesion of the right
• Damage before the optic chiasm causes loss of
vision in the visual field of the same side only.
• Damage in the chiasm causes loss of vision
laterally in both visual fields (bitemporal
hemianopia). It may occur in large pituitary
• Damage after the chiasm causes loss of vision on
one side but affecting both visual fields: nasalsame ½ ; temporal – opp ½
• Ask the patient to cover one eye while the
examiner tests the opposite eye
• The examiner wiggles the finger in each of
the four quadrants and asks the patient to
state when the finger is seen in the
• The examiner's visual fields should be
normal, since it is used as the baseline.
Cranial Nerve III - Occulomotor
• ORIGIN: Originates from the oculomotor nucleus
located in the rostral midbrain at the level of the superior
• COURSE: Fibres leaving the occulomotor nucleus
travel ventrally in the tegmentum of the midbrain passing
through medial portion of the cerebral peduncle to emerge
at the junction of the midbrain and pons.
• Upon emerging from the brainstem the oculomotor nerve
passes between the posterior cerebral and superior
cerebellar arteries and pierces the dura mater to enter the
• The nerve runs along the lateral wall of the cavernous sinus just
superior to the trochlear nerve and enters the orbit via the superior
• Within the orbit, CN III fibers pass through the tendinous ring of the
extraocular muscles and divide into superior and inferior divisions.
• The superior division ascends lateral to the optic nerve to innervate
the superior rectus and levator palpebrae superioris muscles on their
• The inferior division of CN III splits into three branches to innervate
the medial rectus and inferior rectus muscles on their ocular surfaces
and the inferior oblique muscle on its posterior surface.
• The somatic motor component of CN III innervates the
following four extraocular muscles of the eyes:
Ipsilateral inferior rectus muscle
Ipsilateral inferior oblique muscle
Ipsilateral medial rectus muscle
Ipsilateral superior rectus muscle
• The remaining extraocular muscles, the superior oblique and lateral
rectus muscles, are innervated by the trochlear nerve (CN IV) and
abducens nerve (CN VI), respectively
• The somatic motor component of CN III also innervates the Bilateral
levator palpebrae superioris muscles. These muscles elevate the
• Viseral motor component:
Provides parasympathetic innervation of
the constrictor pupillae and ciliary muscles
of the eye. The visceral motor component of
CN III is involved in the pupillary light and
• The reaction of the pupils to light and
• In the direct light reflex, the normal pupil
reflexly contracts when a light is shown into
the patient's eye
• The nervous impulses pass from the retina
along the optic nerve to the optic chiasma
and then along the optic tract
• Before reaching the lateral geniculate body,
the fibers concerned with this reflex leave
the tract and pass to the pretectal nuclei
• The pretectal nucleus in turn projects
bilaterally to the Edinger-Westphal nucleus
• Preganglionic parasympathetic fibers from
each half of the Edinger-Westphal nucleus
then project to the ciliary ganglion of the
• Post-ganglionic parasympathetic fibers exit the ciliary
ganglion to innervate the constrictor pupillae muscle of
the ipsilateral eye
• Due to the bilateral projections from the pretectal nuclei
to the Edinger-Westphal nuclei, light shined into one eye
produces pupillary constriction in both eyes
• Direct pupillary light reflex - response in the stimulated
• Consensual pupillary light reflex - response in the opposite
Pupillary eye reflex - test
• The patient stares into the distance as the
examiner shines the penlight obliquely into
• Pupillary constriction should be noted on
the eye examined (direct response)
and on the opposite eye (consensual
Testing the oculomotor nerve
• Cranial nerves III, IV and VI are usually tested together
• The examiner typically instructs the patient to hold his
head still and follow only with the eyes a finger or penlight
that circumscribes a large "H" in front of the patient
• By observing the eye movement and eyelids, the examiner
is able to obtain more information about the extraocular
muscles, the levator palpebrae superioris muscle, and
cranial nerves III, IV, and VI.
LMN Lesions- Oculomotor
• Due to the close proximity of the oculomotor and EdingerWestphal nuclei and the fact that the fibers of both
components travel together all the way to the orbit of the
eye, a LMN lesion will most likely affect both components
of CN III
• Downward, abducted eye on the affected side due to the
unopposed actions of the superior oblique and lateral
• Strabismus as a result of extraocular muscle paralysis.
This leads to diplopia (double vision).
• Ptosis (eyelid droop) on the
affected side due to inactivation
of levator palpebrae superioris
muscle and the unopposed
action of the orbicularis oculi
muscle (CN VII)
• The patient may compensate
for the ptosis by contracting the
muscles of the forehead to raise
the eyebrow and lid.
• Dilation of the pupil on the affected side
due to decreased tone of the constrictor
• Loss of the accomodation reflex on the
Cranial Nerve IV: Trochlear
• ORIGIN: Fibres emerge from the dorsal
midbrain and enter the orbits via the
superior orbital fissures.
• The fibers of the trochlear nerve originate
from the trochlear nucleus located in the
tegmentum of the midbrain at the level of
the inferior colliculus.
• The nucleus is located just ventral to the
• Fibers leaving the trochlear nucleus travel dorsally to
wrap around the cerebral aqueduct
• All fibers of the two trochlear nerves decussate and exit
the dorsal surface of the brainstem just below the
contralateral inferior colliculus.
• Then trochlear nerve curves around the brainstem in the
subarachnoid space and emerges between the posterior
cerebral and superior cerebellar arteries (along with CN
• • The trochlear nerve then enters and runs along the
lateral wall of the cavernous sinus with CN III, V, and VI.
• From the cavernous sinus the trochlear nerve enters the
orbit through the superior orbital fissure
• Innervate the superior oblique muscle along its proximal
• The only nerve to exit from the dorsal surface of the brain.
• Is the only nerve in which all the lower motor neuron
• Has the longest intracranial course.
• Has the smallest number of axons.
• The superior oblique muscle normally depresses,intorts,
and abducts the eye
• Damage to the trochlear nerve will present as Extorsion
(outward rotation) of the affected eye due to the unopposed
action of the inferior oblique muscle.
• Vertical diplopia (double vision) due to the extorted eye
• Weakness of downward gaze most noticeable on mediallydirected eye. This is often reported as difficulty in
• Head tilt: patient will often tilt his head
opposite the side of the affected eye in an
attempt to compensate for the outwardly
• Due to its long peripheral course around
the midbrain CN IV is particularly
susceptible to head trauma.
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
Cranial nerve V Trigeminal
• It is the fifth cranial nerve and largest of all cranial nerves.
• Type → Mixed so both Motor & Sensory.
• ORIGIN AND COURSE: 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
• 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.
• Ophthalmic Nerve (V1) → Purely Sensory
• Maxillary Nerve (V2) → Sensory.
• Mandibular Nerve (V3) → Mixed and
consisting of two roots
It is one of the divisions of trigeminal nerve.
- It is purely a sensory nerve.
- Arises from the convex anterior margin of
- 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.
• 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
• 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.
1) Within cranium: Meningeal. It supplies duramater of middle and
partly in the anterior cranial fossa.
2) In the pterygopalatine fossa:
3) Posterior superior alveolar.
3) In the infraorbital canal:
i. Middle superior alveolar.
ii. Anterior superior alveolar.
4) In the face:
3. Superior labial.
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
1) From the trunk, i.e. before division:
i) Nervous spinous or meningeal branch
ii) Nerve to medial pterygoid.
2) From anterior divisions:
i) Deep temporal
ii) Nerve to lateral pterygoid
Sensory branch: Buccal nerve and skin
3) From posterior division:
i) auriculo temporal
ii) lingual www.indiandentalacademy.com
• 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.
1) Nerve to myolohyoid
3) Incisive branch
4) Dental branch www.indiandentalacademy.com
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
The motor root of trigeminal supplies the
muscles of mastication and can be tested by
palpating the temporalis and masseter
during clenching movements.
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
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.
It 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.
Cranial nerve VI-Abducens 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
• 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.
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
Effects of paralysis:
– Convergent squint due to unopposed action of medial rectus.
– Often diplopia with convergent squint will be present.
Cranial nerve VII- Facial nerve
• Type of nerve: It is a mixed nerve
consisting of two roots – sensory and motor
roots. The sensory root is known as Nervus
• Developmental representation: It is the
nerve of second branchial arch.
• Branches of distribution:
– Within facial canal
– Nerve to stapedius muscle.
– Chorda tympani nerve.
– Just at its exit from stylomastoid foramen.
– Posterior auricular.
– Nerve to stylohyoid.
– Nerve to posterior belly of diagastric.
– In the face:
– Marginal mandibular.
• Supra nuclear lesions- Hemiplegia.
• Infra nuclear lesions- Bells palsy.
VIII Nerve- Vestibulocochlear
• Type: Special sensory nerve and nerve of hearing and
• Have two components vestibular component and cochlear
• ORIGIN: Cochlear nerve ( two nuclei) ventral cochlear
and dorsal cochlear nuclei.
• Vestibular nerve (four nuclei) superior, inferior, medial,
• COURSE: The vestibulocochlear nerve along with two
roots of facial nerve after emergence from the brain stem
runs laterally to internal acoustic meatus accompanied by
internal acoustic branch of basilar artery and
• In the meatus the motor root of facial nerve lies on upper
and anterior surface of vestibulocochlear and the sensory
root lies between them.
• Then the vestibulocochlear nerve divides into two
components- (a) Vestibular and (b) Cochlear nerves.
• The vestibular nerve is sensory from
receptors in the inner ear that provide
information concerning movement of the
body, balance, and body position in relation
to gravitational force.
• The cochlear nerve is sensory from auditory
(hearing) receptors in the cochlea of the
• Vestibulocochlear nerve is frequently injured
along with facial nerve in fracture of middle
cranial fossa involving internal acoustic meatus.
• Nerve may be injured by violent blows of the head
or by loud explosions and deafness may occur.
• Tumors at cerebello-pontine angle may involve
both the facial and vestibulocochlear nerve.
• Disturbances in the vestibular nerve function include
giddiness(VERTIGO) and NYSTAGMUS. Vestibular nystagmus is
uncontrollable rhythmic oscillations of the eyes. This form of
nystagmus is essentially a disturbance in reflex control of the
extraocular muscles, which is one of the function of the semicircular
canals. The causes of vertigo include diseases of the labrynth, lesions
of the vestibular nerve and cerebellum, multiple sclerosis, tumors and
vascular lesions of brainstem.
• Disturbances in the cochlear nerve include deafness and tinnitus. Loss
of hearing may be due to defect in the auditory conducting mechanism
in the middle ear, damage to receptor cells in spinal organ of corti in
cochlea, lesions of the cochlear nerve due to acoustic neuroma and
trauma, or lesion of the cerebral cortex of temporal lobe due to
• Rinne’s test: vibrating tuning fork is held in the
ear and then placed on the mastoid process
patient is asked to compare the relative loudness
of the two.
• Weber’s test: vibrating tuning fork is placed in
middle of forehead – the sound will be heard
better in the middle ear diseased side than on the
IX Nerve- Glossopharyngeal
• Mixed nerve
• Deep origin: The nuclei are: 1. Upper part of nucleus ambigus: It
gives branchiomotor fibres. 2. Inferior salivatory nucleus: origin of
parasympathetic secretomotor fibres to parotid gland.
• Upper part of nucleus of spinal tract of trigeminal nerve: for general
• Upper part of tractus solitarius: for special sense taste (special
Visceral afferent) and other general visceral sensations from
posterior one third of tongue, tonsil, palate, oral part of pharynx.
• Superficial origin: The nerve emerges out as two or three rootlets
from the posterolateral sulcus of medulla oblongata above the rootlets
of vagus nerve.
• Glossopharyngeal nerve is not involved separately usually. It may be
injured along with tenth nerve.
• Acute pharyngitis may cause referred pain in the ear but
inflammation of pharyngotympanic tube must be excluded.
• Reflex contraction of muscles of throat if posterior wall of pharynx is
stimulated and 9th nerve can be tested in this way.
• Taste sensation of posterior one-third of tongue will be lost in case of
involvement of 9th nerve.
• After a series of coughing carotid sinus may be subjected to pressure
and results in syncope or cardiac arrest. This is due to stimulation of
cardioinhibitory centre reflexly by sinus nerve.
X Nerve- Vagus
• The vagus nerve supplies motor fibers to constrictor
muscles of the pharynx, intrinsic muscles of the larynx,
and involuntary muscles of the bronchi, heart, esophagus,
stomach, small intestine, and part of the large intestine.
Secretory motor fibers of the vagus supply the pancreas
and secretory glands of most of the alimentary canal. The
vagus is sensory from the laryngeal mucosa, heart, lungs,
esophagus, stomach, small intestine, and part of the large
intestine. In addition, vagal sensory fibers convey taste
from the epiglottis and blood pressure and chemistry
information from the aorta. The ninth and tenth cranial
nerves are tested together because their functions overlap.
• Auricular branch of vagus is irritated by scratching, or by
earwax or syringing the ear with warm water. This
irritation may cause reflex vomiting and also stoppage of
heart by reflex irritation of vagus.
• Recurrent laryngeal nerve may be injured during
operation on thyroid and application of ligature of inferior
thyroid artery. It may also be compressed during
enlargement of thyroid, specially a growth. Its affection
causes hoarseness of voice.
• Vagotomy i.e. section of anterior and posterior or vagal
trunks are sometimes done in treatment of peptic ulcer.
XI Nerve- Spinal accessory
• The spinal accessory nerve, cranial nerve XI,
innervates the sternocleidomastoid and trapezius
muscles. It is composed of spinal fibers
originating in the anterior horn cells of the first
five cervical cord segments and an accessory
component, which travels briefly alongside the
vagus nerve. The dorsal and ventral roots from the
first five cervical cord segments unite to enter the
skull through the foramen magnum and exit
through the jugular foramen.
• The eleventh cranial nerve supplies some motor
fibers to the muscles of the larynx and pharynx via
the pharyngeal plexus (C.N. IX-X-XI), but its
principal distribution is motor to the
sternocleidomastoid and trapezius muscles. The
sternocleidomastoid turns the head to the opposite
side, and the trapezius muscle elevates the
shoulder on the same side.
• When the sternocleidomastoid and trapezius are weak on
the same side, an ipsilateral peripheral accessory palsy,
involving cranial nerves X and XI, is implied as may be
seen with a jugular foramen tumor, ie, glomus tumor or
neurofibroma. Because the cerebral hemisphere innervates
the contralateral trapezius and ipsilateral
sternocleidomastoid, a large right hemisphere stroke will
result in weakness of the left trapezius and right
sternocleidomastoid. Bilateral wasting of the
sternocleidomastoid may be seen with myopathic
conditions such as myotonic dystrophy and polymyositis or
motor neuron disease, the latter usually associated with
XII Nerve- Hypoglossal
• The hypoglossal nerve is a pure motor nerve,
innervating the muscles of the tongue. It obtains
supranuclear innervation from the contralateral
motor cortex. The nucleus of the hypoglossal
nerve sits in the medial aspect of the medulla, near
the floor of the fourth ventricle and exits the skull
through the hypoglossal canal.
• Tongue deviation, combined with wasting on the side to
which it is deviated, implies a unilateral, lower motor
neuron, hypoglossal nucleus or nerve lesion as may be
seen with syringobulbia (a degenerative cavity within the
brainstem), with basilar meningitis, or foramen magnum
tumor. If the tongue deviates and is of normal bulk, one
should consider an upper motor neuron lesion, such as
stroke or tumor in the hemisphere contralateral to the side
of deviation, and look for associated hemiparesis on the
side of tongue deviation.
• HUTCHISON’S CLINICAL METHODS 23 EDITION.
• ESSENTIALS OF NEUROANATOMY- A K DATTA.
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HAND BOOK FOR EMERGENCY PHYSCIANS BY CAMBRIDGE
• INDIAN JOURNAL OF NEUROTRAUMA -2007 VOL 4.
• THE NEUROLOGICAL EXAMINATION- RAYMOND A.MARTIN
• ESSENTIALS OF CLINICAL NEUROLOGY: HEAD TRAUMA- L A