Describe the course and distribution of the facial nerve.

                       Cranial Nerves

12 pairs of cranial nerves. Passes through the foramina, fissures in the skull.

1. Olfactory nerve - cribriform plate of ethmoid

2. Optic nerve - optic canal

3. Oculomotor nerve - superior orbital fissure

 4. Trochlear nerve - superior orbital fissure

5. Trigeminal nerve 

     i. Ophthalmic - superior orbital fissure

     ii. Maxillary - foramen rotundum

    iii. Mandibular Pons - foramen ovale

6. Abducent nerve - superior orbital fissure

7. Facial nerve - internal acoustic meatus, facial canal, stylomastoid foramen

8. Vestibulocochlear nerve - internal acoustic meatus

9. Glossopharyngeal nerve - jugular foramen 

10. Vagus nerve - jugular foramen

11. Accessory nerve - jugular foramen

12. Hypoglossal nerve - hypoglossal canal

👀 Some cranial nerves are sensory  Eg: 1,2,8

👀 Some cranial nerves are motor  Eg: 3,4,6,11,12

👀 Some cranial nerves are both  Eg: 5,7,9,10

 Cranial nerves have NO SYMPATHETICS. Some possess parasympathetics

 Eg:

         i. Oculomotor nerve  - Edinger Westphal nucleus

        ii. Facial nerve  - Superior salivatory and lacrimal nuclei 

        iii. Glossopharyngeal nerve  -  Inferior salivatory nucleus 

         iv. Vagus nerve  -  Dorsal nucleus of vagus

 Optic nerve is an outgrowth of brain that emerges from the diencephalon – not from the brainstem as other cranial nerves

 There are only 9 pairs of cranial nerves that emerge solely from the brainstem

                          Facial Nerve

Sensory and motor

3 nuclei

1. sensory 

            In upper part of tractus solitarius (7,9,10) - supplies taste fibres from anterior 2/3 of tongue, floor of mouth & palate

2. main motor

           In lower part of pons -muscles of facial expression, auricular

muscles, Stapedius, posterior belly of digastric, stylohyoid

3. parasympathetic

         *  lacrimal nucleus – lacrimal gland

         *  Superior salivatory nucleus - submandibular gland, sublingual gland,nasal & palatine glands

Facial Nerve

👀  The facial nerve consist of a motor and a sensory root. The fibers of the motor root first travel posteriorly around the medial side of the abducent nucleus.

👀 Then they pass around the nucleus beneath the facial colliculus in the floor of the 4 th ventrical and finally pass anteriorly to emerge from the brain stem between the pons and medulla oblongata.

👀  They pass laterally in the posterior cranial fossa with the vestibular cochlear nerve and enter in to internal acoustic meatus.

👀  At the bottom of the meatus, the nerve enters the facial canal and runs laterally through the inner ear.

👀  On reaching the medial wall of the tympanic cavity, the nerve expand to form the sensory geniculate ganglion and tern sharply backward above the promontory.

👀  At the posterior wall of the tympanic cavity the facial nerve tern downward on the medial side of the aditus of the mastoid antrum, descend behind the pyramids, and emerge from the stylomastoid foramen.

👀  At the geniculate ganglion, lacrimatory fibers of the superior salivatory and lacrimatory nucleus get separated and form the greater petrosal nerve.

👀  Then it enter in to middle cranial fossa and leave it through foramen lacerum. 

👀 At the midway of the foramen lacerum it enter in to pterigoid canal with deep petrosal nerve.

👀  Then it enter in to pterigoid ganglion and supply to the lacrimal glands. 

👀  Main motor fibers of the facial nerve supply to the stapedius muscle before emerge from the stylomastoid foramen.

👀  Chorda tympani nerve runs through middle ear between malleus and incus and enter in to infra temporal fossa.

👀  Then it accompanies the lingual nerve.

👀  Fibers from the tractus solitarius nucleus supply to anterior 2/3 of tongue and Fibers from superior salivatory nucleus supply to both sublingual and submandibular gland.

👀  After emerge, between stylomastoid foramen motor fibers supply to the stylohyoid, posterior belly of digastrc, auricular muscles, and whole facial expression muscles exept levator palpebrae superioris.

Clinical

Supranuclear (UMN) lesion

                    - As the upper part of the face receives corticonuclear fibres from both cerebral hemispheres(bilateral innervation)

                    - Only lower part of opposite side of face is paralyzed.                                                                  - Loss of taste

Infranuclear (LMN) lesion

                     - Whole face of same side get paralyzed.                                                                                           - Lower eyelid will drop.                                                                                                                       - Wrinkles disappear in forehead.                                                                                                       - Food accumulate teeth & cheek.