Cranial Nerves VI-XII Flashcards
Describe the pathways of the 3 branches of the Trigeminal Nerve after branching off the Trigeminal Ganglion
Ophthalmic: Through Cavernous sinus then through Superior Orbital Fissure
Maxillary: Through Cavernous Sinus then through Foramen Rotundum
Mandibular: Through Foramen Ovale into Infratemporal Fossa
Identify 2 important distal sensory divisions of Va
- Frontal Nerve, which gives rise to Supraorbital and Supratrochlear nerves
- Nasociliary Nerve (Hutchinson’s Sign)
(Also Lacrimal nerve)
Identify 2 important distal sensory divisions of Vb
- Infra-orbital Nerve
- Superior Alveolar Nerves
Identify 3 important distal sensory divisions of Vc
- Auriculotemporal nerve
- Lingual nerve (general sensation from anterior 2/3 of tongue)
- Inferior Alveolar Nerve and Mental Nerve
(Distal motor divisions go to supply Muscles of Mastication)
Not all cases of Opthalmic Shingles (Reactivation of VZ in Va region) extend down into nose.
When does this happen?
Only happens when Nasocliary branch of Va is involved
This nerve therefore innervates the tip of nose and also around front of eye
What is Hutchingon’s sign?
What is significant about this?
- Presence of crusting and vesicular rash at tip of nose
- Increases risk of Opthalmic Shingles affecting front of eye
Describe the inwards to outwards path of Infra-orbital branch of Vb and state why it is vulnerable to injury
(Sensory nerves)
- Passes through floor of orbit, hence at risk of injury in orbital fractures
- Exits through Infra-orbital Foramen (visible externally)
Describe the outwards to inwards path of the Superior Alveolar branches of Vb
(Sensory nerves)
- Run up Maxilla, carrying sensory information from Teeth and Gums
- Joins Infraorbital Nerve to connect to CNS
(Therefore damage to Indra-orbital nerve can lead to loss of sensation in Vb and Vc dermatomes)
State the region of head innervated by the;
- Auriculotemporal nerve
- Lingual nerve
- Inferior Alveolar and Mental nerves
- Auriculotemporal: Parts of lateral scalp and ear
- Lingual: Anterior 2/3 of tongue
- Inferior Alveolar and Mental nerves: Lower teeth, gums, lip, chin
Describe the inward to outward pathway of Inferior Alveolar nerve and its relationship to the Mental nerve
(After Auriculotemporal and Lingual branches have come off)
(Sensor nerve)
- Enters Mandibular Foramen and passes through Mandibular Canal (In Mandibular body)
- Emerges through Mental Foramen, to become the Mental Nerve
Why do dentists insert local anaesthetic into the Inferior Alveolar Nerve near Mandibular Foramen?
Why does your tongue often go numb in this process?
- Prevents sensory information from Mental and IO nerves being carried to CNS, preventing pain
- Due to proximity of Lingual nerve to IO nerves, Lingual nerve is often also affected by local anaesthetic
The Facial Nerve comes off the Pons. It has motor, sensory and parasympathetic function
What are its target tissues for each function?
Motor- Facial expression muscles
Sensory- Taste from anterior 2/3 of tongue
Parasympathetic- Glands (Salivary, Lacrimal)
How do patients with a facial nerve lesion present?
- Unilateral facial droop (whole half of affected side)
- May have other symptoms too
List 6 causes of Facial Nerve Lesion
- Basal skull fracture (involving petrous bone)
- Middle Ear Disease
- Lesions in/ around internal acoustic meatus
- Posterior cranial fossa tumours
- Parotid disease
- Inflammation in facial canal-> Facial nerve palsy (E.g Bell’s Palsy, Ramsay Hunt syndrome)
(All these causes affect the facial nerve along its route after leaving brainstem)
How do Ramsay-Hunt Syndrome patients present in 2 ways?
- Presence of vesicles/ rash within external ear (related to Varicella Zoster infection)
- Ipsilateral face droop
Outline the path off the Facial Nerve
- Comes off Pons and passes through Internal Acoustic Meatus into Petrous Bone
- In Petrous Bone, gives off 3 branches, then runs through Facial Canal (closely related to Middle Ear)
- Emerges through Base of Skull via Stylomastoid Foramen, runs through Parotid Gland, then gives off Extra cranial branches to muscles of facial expression
Describe the path of the Facial nerve once it enters the Petrous Bone and how it gives of 3 branches here
- Runs through Geniculate Ganglion where the parasympathetic Greater Petrosal branch comes off and emerges from Petrous Bone
- Runs through Middle Ear Cavity and gives off a motor branch, the Nerve to Stapedius
- Runs through Middle Ear cavity and gives of a sensory AND parasympathetic branch, the Chorda Tympani (Parasympathetic fibres need to get to salivary glands)
How do we tell the difference between a Stroke and Ipsilateral Facial Droop?
Stroke- Only lower half of face affected
Facial Droop- Whole half of face affected
Strokes only affect 1 hemisphere at a time and are central in the brain. Facial nerve lesions occur after facial nerve has left the pons.
Use this information to explain why Strokes only affect the Contralateral Lower Half of Face
- Stroke affects motor fibres before they leave the Pons, thus affecting Contralateral Motor Nuclei to Upper and Lower face muscles
- Ipsilateral ‘back up’ fibres ONLY synapse with Motor Nuclei to Upper face muscles (NOT with Lower face nuclei)
- Therefore Upper Half of face is only supplied by ‘Ipsilateral back up’
Strokes only affect 1 hemisphere at a time and are central in the brain. Facial nerve lesions occur after facial nerve has left the pons.
Use this information to explain why Facial Nerve Lesions affect the Contralateral Whole Face
Lesion affects motor fibres AFTER they leave Pons, so absolutely no motor impulses reach Face muscles, regardless of whether they are Upper or Lower face
(Ipsilateral back up fibres affected as well, so upper face muscles affected too)
The Vestibulocochlear is a special sensory nerve that arises from the Pons.
Describe its path from the pons
- Comes off pons, travels short distance then through Internal Auditory Meatus into Petrous Bone
- In PB, branches to Innervate the Vestibular System and Cochlea
How do we test the Vestibulocochlear nerve?
- Bedside hearing tests (whisper/ finger rub)
- Tuning fork testing
How can patients with a Vestibulocochlear nerve lesion present?
- Hearing loss
- Possibly Dizziness/ Vertigo
- Possibly Tinnitus
What are 4 possible causes of a Vestibulocochlear nerve lesion?
- Vestibular Schwannoma/ Acoustic Neuroma (and other posterior cranial fossa tumours)
- Occlusion of labyrinthe artery
- Basal skull fracture (involving petrous bone)
- Brainstem lesion (pons)
