Cranial Nerves

12 Pairs of Cranial Nerves.

I Olfactory nerve.

The olfactory nerve (I) is attached to the under surface of the frontal lobe; its connections pass to the temporal lobe and elsewhere.

II Optic nerve.

The optic nerve (II) is an outgrowth of the diencephalon and is attached to structures in the wall and floor of the third ventricle.

III Oculomotor nerve.

IV Trochlear nerve.

V Trigeminal nerve.

  • Mostly Sensory
    • Sensation of most of head and neck
  • Motor
    • Small portion —> Mastication

Semilunar Ganglion=Gasserian Ganglion=Trigeminal Ganglion

  • Root of sensory fibers of trigeminal nerve.
  • A ganglion in pocket of dura (Meckel's cavity) lateral to the cavernous sinus. It passes posteriorly between the superior petrosal sinus in the tentorium and the skull base and enters the pons.

Branches:

  • Ophthalmic Nerve
    • Sensory
    • Through Sup Orbital Fissure
    • Nasocilliary brach —> Lacrimal Gland
  • Maxillary Nerve
    • Sensory
    • Through Foramen Rotundum
  • Mandibular Nerve
    • Mixed(Sensory and Motor)
    • Motor nerves involved in mastication
    • Through Foramen Ovale
Physical Exam

Motor Function :

  1. Palate the temporalis and masseter muscles as the patient bites down hard.
  2. Then have the patient open their month and resist the examiner's attempt to close the month.
    1. If there is weakness of the pterygoids the jaw will deviate towards the side of the weakness.
Reflexes

Corneal Reflex:
Corneal stimulation evokes a protective blink response

  • The afferent axons ( اعصاب آوران )
    • Ophthalmic branch of nerve V
    • Synapse in the spinal tract & nucleus of V
  • The efferent axons ( اعصاب وابران )
    • Facial (VII) nuclei, where motor neurons that project to the orbicularis oculi muscles are activated

Jaw jerk reflex

  • Monosynaptic (stretch) reflex for the masseter muscle.
  • The afferent axons ( اعصاب آوران )
    • Sensory axons of Mandibular nerve. ( CN V )
    • Collaterals to mesencephalic nucleus of CN V
  • The efferent axons ( اعصاب وابران )
    • Motor axons of CN V

When performing Jaw Reflex—> Normally there is no movement. If there is a jaw jerk it is said to be positive and this indicates an upper motor neuron lesion.

VI Abducent nerve.

VII Facial nerve.

Originates from Cerebellopontine Angle
Also CN VIII originates from CP angle.
Nuclei

  • Motor Nuclei
    • Lower part of the pons
  • Sensory Nuclei
    • Close to motor nuclei
    • Efferent from parasympathetic
    • —>Geniculate Ganglion
    • Sensation of 2/3 any of tongue
  • Parasympathetic Nuclei
    • Superior salivatory
    • Lacrimal nuclei
Ganglions:
Course of Facial n.
  • Through floor of 4th ventricle
  • Emerge from the anterior surface of the brain between the pons and the medulla oblongata
  • The facial nerve leaves the skull through the stylomastoid foramen and immediately enters the deep part of the parotid gland where it gives off its branches.
  • Internal acoustic meatus
  • Facial canal
Geniculate Ganglion
  • Medial Wall of Tympanic Canvity
  • At the bottom of the internal acoustic meatus, the facial nerve enters the facial canal and runs toward stylomastoid foramen
  • At first it travels laterally, between the cochlea and vestibule, towards the medial wall of the tympanic cavity.
  • From here, it then bends suddenly backward and arches downward behind the tympanic cavity to the stylomastoid foramen.
  • The point where it changes its direction is named the 'geniculum'; here it presents a reddish gangliform swelling, the genicular ganglion.
Understand Central vs Peripheral Palsy
  • It's all about the motor nucleus of Facial n.
    • This is a complexion of a neurons. ( fair enough!!! )
    • These neurons are lower motor neuron.
      • That means they have synapses with Upper motor neurons which come from the cortex.
  • Keep in mind that Facial N. motor nucleus has two parts:
    • Dorsal Part
      • Receiving UMN from bilateral cortex.
      • Innervating muscles of the upper face
    • Ventral Part
      • Receiving UMN impulses from contralateral cortex ONLY.
      • Innervating muscles of the lower face.

That's why with central facial n. lesion( a stroke or lesion in the cortex ) ==> Contralateral lower face palsy
With Peripheral facial n. lesion( tumor, Bell's Palsy ) ==> Unilateral lower and upper part palsy.

This picture is wrong! Ventral Part recieves from ONLY contralateral cortex.

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Disease Cause Symptoms
Nuclear(Peripheral)
Lyme Disease Borrelia Burgdorferi History of tick exposure, rash, or arthralgias; exposure to endemic area
Otitis Media Infectious Conductive hearing loss, fever, otalgia
Ramsy Hunt Syndrome HZV Intense Pain, Vesicular eruption in ear canal or pharynx
Sarcoidosis, Guillain-Barré Autoimmune Bilateral
Tumors Parotid Gland
Supranuclear Forehead spared
MS Demyelination More neurologic defecit
Stroke Ischemia or Hemorrhage
Tumours GBM, CNS primary, metastasis to brain

VIII Vestibulocochlear nerve.

IX Glossopharyngeal nerve.

  • Motor; Sensory and Parasympathetic fibers
  • Emerges from posterior medulla onlongata
  • Close relation to CN X and XI
  • These three nerves merges out of Jugular Foramen
  • Descends through lateral wall of pharynx
    • Between Carotid a. and Jugular v.

Motor
Stylopharyngeal m.

Sensory

  • Sensation of soft palate
  • post 1/3 of tongue TASTE
  • Petrous Ganglion —> gives out Jacobson n. ( Tympanic n. )
    • Sensation of tympanic membrane
    • Eustachian Tube
    • Mastoid Region
  • Also receptors from Carotid Body
Nerve.png
Gag Reflex
  • Efferent
    • Glossopharynegeal n.
  • Afferent
    • Glossopharyngeal n. and Vagus n.

Parasympathetic

  • Preganglion fibers leave CN IX at Petrous Ganglion
    • —> Jacobson n. or Tympanic n.
    • —> also Lesser Sup Petrousal n.
    • Then both —> —> Otic Ganglion
      • Otic Ganglion lies right below Foramen Ovale
    • Postganglionic fibers:
    • —> to Parotid Gland

X Vagus nerve.

XI Spinal accessory nerve.

XII Hypoglossal nerve

  • Motor nerve of the tongue
  • Anterior to the inferior aspect of the hyoglossus muscle and then to the lateral aspect of the genioglossus m.
  • Injury ==>
    • Paralysis and atrophy of the ipsilateral oral tongue
      • Tongue deviates to the paralyzed side upon protrusion
        • <== Unopposed contralateral genioglossus muscle