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Cranial nerves pathways

I-XII

BYProf. Dr. Abdul Waheed AnsariChairperson & Prof. Anatomy,

RAKCODS/RAKCOMS.

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There are 12 pairs of cranial nerves

• Purely sensory cranial nerves are :- Olfactory/Optic and Auditory.

• Purely motor cranial nerves are:Occulomotor/Trochlear/Abducent

/Hypoglossal

• Mixed cranial nerves are:- Trigeminal/ Facial/Glossopharyngeal/Vagus.

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I – Olfactory nerve• It arises from the neuroepithelium of nasal cavity. • 18/20 Fila olfactoria pass through the cribriform plate

of ethmoid and enters the anterior cranial fossa.• It synapses with the olfactory bulb.• It proceeds as olfactory tract, it ends at anterior

perforated substance and uncus.• It by passes the thalamus and ends in the limbic

system.• Injury to the anterior cranial fossa may damage these

nerves and leads to anosmia and CSF rhinorrhea

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Anosmia is the result after injury to the cribriform plate of ethmoid

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II- Optic nerve• It carries vision and color discrimination.• Developmentally optic nerve and retina are

outgrowths of brain.• Optic nerve arises from the rods/cones/bipolar

neurons of retina, optic nerve passes through the optic canal and form optic chiasma, it follows as optic tract and ends in the lateral geniculate ganglion.

• Fibers arising from lateral geniculate ganglion are projected to visual cortex area 17/18/19 calcarine sulcus/occipital cortex.

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Lesions of optic pathways• Complete lesion of optic nerve of one side leads to

complete blindness in the corresponding eye.• Compression of optic chiasma causes bitemporal

hemianopia because the nasal fibers from both sides are interrupted.

• Lesion of optic tract of one side leads to corresponding nasal and contralateral temporal hemianopia.

• Lesion of optic radiation of one side leads to corresponding nasal and contralateral temporal hemianopia

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III- Oculomotor nerve• It supplies all extra ocular muscles except lateral rectus

and superior oblique.• It is a purely motor nerve. Its nucleus is situated at the

superior colliculus level of mid brain, at the floor of periaqueductal gray.

• It has an accessory nucleus situated medial to the main nucleus, it is called as EW nucleus/Edinger Westphal nucleus, it is parasympathetic nucleus for sphincter pupillae.

• Oculomotor nerve appears at the interpeduncular fossa and passes through the lateral wall of cavernous sinus and enters the orbit through the SOF.

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Injury to oculomotor nerve result in

• Ptosis- drooping of the eyelid due to paralysis of LPS

• External squint due to unopposed action of lateral rectus and superior oblique.

• Mydriasis due to paralysis of sphincter pupillae

• Diplopia- double vision• Loss of accommodation & light reflex.

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IV- Trochlear nerve

• Its nucleus is situated at the inferior colliculus level in the periaquaductal gray, it emerges dorsally and enters the lateral wall of cavernous sinus and supplies the superior oblique muscle.

• Injury to the IV nerve result in paralysis of superior oblique, the affected eye rotates medially producing diplopia.

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V- Trigeminal nerve

• It is a mixed cranial nerve , attached to the basilar part of pons. It has a ganglion Gasserian ganglion situated in the cavum trigeminale. It divides into three roots, hence its name.

• Ophthalmic V1 • Maxillary V2• Mandibular V3

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There are four nuclei, one motor and 3 sensory for V nerve

• Motor nucleus is situated at the pons.• Sensory nuclei are:-• Mesencephalic nucleus in the mid brain• Main sensory nucleus in the upper pons• Spinal nucleus in the lower pons, medulla and

upper cervical spinal cord.• The V1 emerges through the SOF.• The V2 pass through the foramen rotundum.• The V3 exits through the foramen ovale.

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Cranial nerves in the lateral wall of cavernous sinus

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VI – Abducent nerve

• Its nucleus is situated in the pons, at the facial colliculus level in the floor of IV ventricle.

• Its fibers emerge at the pontomedullary junction.

• The nerve passes through the lateral wall of cavernous sinus and enters the orbit through the SOF and supplies the lateral rectus.

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Applied anatomy

• In a lesion of the abducens nerve, the patient cannot turn the eye laterally, causing internal strabismus, diplopia.

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VII- Facial nerve• It is motor to muscle of facial expression and

sensory to presulcal area of tongue and secretomotor to submandibular and sublingual glands.

• The motor nucleus is situated in the pons.• Taste nucleus is the nucleus of tractus solitarius

situated in the medulla.• The secretomotor fibers/ parasympathetic fibers

arises from superior salivatory nucleus situated adjacent to DVN( dorsal vagal nucleus)

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The facial nerve exits through the stylomastoid foramen

• The chorda tympani nerve emerges out through the tympanosquamous fissure and joins the lingual nerve in the infratemporal fossa, to be carried to the presulcal area of tongue for special taste sensations.

• The chorda tympani also carries secretomotor fibers for submandibular/sublingual glands. The preganglionic fibers get relayed at the submandibular ganglion.

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Facial nerve injuries

• If the facial nucleus are affected, there may be damage to abducent nucleus/lateral rectus palsy; motor trigeminal nucleus may also be involved( paralysis of muscles of mastication and sensory loss of face.

• Lesion at the internal acoustic meatus, resulting in loss of taste from anterior part of tongue with ipsilateral deafness and facial paralysis.

• Lesion at the facial canal, result in hyperacusis in one of the ear.• If the lesion is at the temporal bone, it result in loss of taste

from anterior third of tongue.• Bell’s palsy if the lesion is at the stylomastoid foramen.

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Features of Bell’s palsy

• Facial asymmetry and affected side is immobile.• The eyebrows are drooped, wrinkles are smoothed

out, palpebral fissure is widened• Food accumulates in the cheek, from paralysis of

buccinator and dribbles.• Platysma and auricular muscles are paralyzed• Tears will flow over lower eyelid and saliva will

dribble from the corner of the mouth.

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Left facial nerve palsy

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VIII-Vestibulocochlear nerve

• It is a purely sensory nerve.• It is a dual nerve.• There are four vestibular

nuclei situated in the floor of VI ventricle.

• There are two cochlear nuclei, dorsal and ventral cochlear nuclei situated dorsal and ventral to the inferior cerebellar peduncle.

• The vestibulocochlear nerve enter through the internal acoustic canal along with the facial nerve and get attached with the cochlea and vestibular apparatus in the internal ear.

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Disturbance of vestibular nerve

• Result in giddiness/vertigo and nystagmus.• Vestibular nystagmus is an uncontrollable

rhthmic oscillation of the eyes.• A patient with vestibular nerve injury cannot

walk in a straight line, with eyes closed.• Disturbance of cochlear nerve produce

deafness and tinnitus.

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IX- Glossopharyngeal nerve• It is a mixed cranial nerve. It exits through the jugular

foramen.• It is nerve of III arch, it supplies stylopharyngeus,

secretomotor fibers to parotid gland and sensory fibers to tonsil, pharynx and posterior 1/3rd of tongue and special taste sensation from post sulcal area and circumvallate papillae.

• The nuclei are :- 1. Nucleus ambiguus/medulla• 2. Inferior salivatory nucleus for otic ganglion• 3. Spinal nucleus of trigeminal nerve• 4. Nucleus of tractus solitarius

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X- Vagus nerve

• It is a mixed cranial nerve, exits through jugular foramen.

• Its nuclei are:-• 1. Nucleus ambiguus – medulla• 2. dorsal vagal nucleus-medulla• 3. nucleus tractus solitarius – medulla• 4. spinal nucleus of trigeminal nerve.

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XI – Accessory nerve• It has two roots, cranial and spinal.• Nuclei are:-• 1. Nucleus ambiguus- medulla• 2. Anterior horn cells of upper 6 cervical nerves.• Lesion of accessory nerve will result in paralysis of

sternomastoid/trapezius muscles; drooping of shoulder, weakness& difficulty in raising the arm above horizontal.

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XII- Hypoglossal nerve

• Its nucleus is situated in the medulla, the hypoglossal triangle.

• The nerve leaves the cranial cavity through the hypoglossal canal.

• It supplies all the tongue muscles except palatoglossus.

• Injury result in unilateral lingual paralysis and hemiatrophy.

• The tip of tongue deviates to the paralyzed side

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Right and left hypoglossal nerve palsy

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References Essential Clinical anatomy- Keith Moore-fourth edition(644-672)

• http://casereports.bmj.com/content/2009/bcr.08.2008.0636.full

• http://12cranialnerves.wordpress.com/cranial-nerve-12-hypoglossal-nerve/

• http://en.wikipedia.org/wiki/Bell's_palsy• http://tsdocs.org/downloads/CranialNerves.p

df• http://www.gwc.maricopa.edu/class/bio201/c

n/cranial.htm

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Sample MCQS

• Paralysis of 3rd, 4th and 6th cranial nerves with involvement of ophthalmic division of trigeminal, localizes the lesion to:

• A. Cavernous sinus• B. Apex of orbit• C. Brainstem• D. Base of skull• E. At Internal acoustic canal

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If both eyes turn in, which CN is likely injured?A. VI B. V.C.III D.IV. E.V

A dysfunction in which of the following nerves would cause anosmia? A. IB. IIC. IIID. IXE. XI

• Which CN is responsible for salivation?

• A. IX• B. XI• C. XII• D. IV• E. III

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If someone had trouble with speech and swallowing and the larynx, which nerve may be to blame?

A. IX.B.X.C.XI.D.XII E.VIII

• A balance dysfunction is probably due to which nerve:

• A. IV• B. V• C. VI• D. VII• E. VIII

• Which cranial nerve is responsible for mastication?

• A. I• B. II• C.III• D. IV• E. V

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Sample MCQS

• A 50-year old man present with complaint of double vision. While testing the patient's right eye movement during a cranial nerve test, the physician noted that the patient cannot elevate the adducted eye. Which of the following muscles is involved?

• A. Superior rectus• B. inferior rectus• C. Lateral rectus• D.Superior oblique• E.Inferior oblique

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If someone could not produce tears, which CN may be damaged?

A. Optic B. Oculomotor C.Facial D. Glossopharyngeal E. Vagus

• Which cranial nerve is called as “Wanderer”?

• A. Vagus• B. Glossopharyngeal• C. Accessory• D. Hypoglossal• E.Facial

• If the Optic nerve is cut at the optic chaism, what kind of deficit to vision will occur?

• A. Tunnel vision& Bitemporal heteronymous hemianopia

• Bilateral blindness• C.Monoocular blindness• D. Contralateral homonymous

hemianopsia• E. bitemporal homonymeous

blindness