Cranial Nerve VII (7)

Cranial Nerve VII (7)

1. Facial Nerve

   • Motor nerve with sensory and parasympathetic components
     • Sensory + para is divided separate from motor division
       • It is called
         • NERVUS INTERMEDIUS
   • Function
     • Motor innervation to muscles of FACIAL EXPRESSION
     • sensation from ant. 2/3 TONGUE and SOFT PALATE
   • Contains parasympathetic fibres synpasing in pterygopalatine and submandibular ganglion
   • Course
     • motor nucleus located in
       • Distal pons
         • (Ant and lat to abducens nucleus)
         • leaves nucleus, pass around abducens nucleus
           • 2 roots of CN7 leave ant. SA of brainstem at pontomedullary junction
             • through cerebellopontine angle
               • enter IAM with VIII (8)
                 • CN7 enters FACIAL CANAL
                   • along medial wall of middle ear
                     • expands to GENICULATE GANGLION
                       • Turns backwards and descends on me.d wall of middle ear
                         • Exits skull via STYLOMASTOID FORAMEN
                       • Greater PETROSAL nerve leaves

2. Disribution of VII - Motor Root

   • innervates
     • STAPEDUS MUSCLE
       • (in middle ear)
   • Through STYLOMASTOID FORAMEN
     • Branches to post. bell of DIGASTRIC + STYLOHYOID
       • Divides into 5 branches
         • 1) Two
           • TEMPORAL
         • 2) Zombies
           • ZYOMATIC
         • 3) Buggered
           • BUCCAL
         • 4) My
           • MANDIBULAR
         • 5) Cat
           • CERVICAL

3. Taste

   • Central Connections
     • 1st ON - from ant. 2/3 tongue and soft palate to
       • GUSTATORY MUSCLE (sup part of nucleus solitarius)
         • cell bodies in geniculate ganglion
     • 2nd ON - ascend ipsilat to THALAMUS
     • 3rd ON - GUSTATORY CORTEX
   • fibres for taste associated with facial nerve exit within
     • NERUS INTERMEDIUS, CHORDA TYMPANI & GREATER PETROSAL NERVES
       • NERVUS INTERMEDIUS ends at geniculate ganglion and taste fibres are conveyed via
         • CHORDA TYMPANI
           • Ant 2/3 tongue
         • GREATER PETROSAL NERVE
           • Soft palate
       • GREATER PETROSAL NERVE
         • branches from GENICULATE GNALGION
           • into PTERYGOPALATINE FOSSA
   • Distribution of VII (Taste fibres)
     • innervates STAPEDIUS
       • STYLOMASTOID FORAMEN
         • CHORDA TYMPARI branches from facial nerve
           • enters middle ear via post wall
             • across TYMPANIC MEMBRANE (between malleous + incus)
               • exits skull via PETROTYMPANIC FISSURE
           • Distributed to tongue with lingual nerve (V3)
             • joins this nerve in intratemporal fossa
     • Distributed with V2 to palatal taste buds

4. Central Connections - Parasympathetic

   • para nucleus lies post and slightly lat to motor nucleus
     • sup. salivatory nucleus
   • Fibres leave sup. salivatory nucleus
     • travel with nervus intermedius
       • GREATER PETROSAL NERVE innervates
         • LACRIMAL GLAND and glands of NASAL MUCOSA
       • CHORDA TYMPANI
         • SUBMANDIBULAR + SUBLINGUAL SALIVARY GLAND
   • Cutaneous Sensation
     • Axons which innervate skin over pinna (outer ear) leave facial nerve at
       • junction of facial canal with stylomastoid foramen
         • 1st ON - cell bodies within GENICULATE GANGLION
           • enter directly into TRIGEMINAL SENSORY NUCLEUS

5. Clinical Consideration - Vestibular Schwannoma

   • benign, slow growing tumour
     • typically arises from vestibular portion of vestibulocochlear nerve
       • Located in cerebellopontine angle
   • Damage to CN VIII causes
     • gradual progressive sensorineural deafness
       • damage to hair cells in cochlear or nerve (VIII)
       • over many months or years
         • may have associated tinnitus (rarely vertigo)
   • >2cm tumours can compress CN V
     • facial pain, numbness, and paraesthesia
   • CN VII Damage + facial weakness
     • UNCOMMON despite marked nerve compression
   • Damage to CN IX, X and XI is rare - only affected by large tumours