PBL 3 Flashcards
where does the facial nerve arise? Describe its intracranial course
Arises in the pons of the brainstem.
It begins as 2 roots: a large motor root and a small sensory root.
The two roots travel through the internal acoustic meatus.
Still inside the temporal bone, the nerve roots leave the internal acoustic meatus and enter the facial canal. Here:
• The 2 roots fuse to form the facial nerve
• The nerve forms the geniculate ganglion (collection of nerve cell bodies)
• The nerve branches to give rise to different nerves before exiting the facial canal and cranium via the stylomastoid foramen .
what is the part of the facial nerve that arises from the sensory root?
intermediate nerve
what is the internal acoustic meatus?
a 1cm opening in the petrous part of temporal bone
what intracranial nerve branches does the facial nerve give rise to in the facial canal along the way?
greater petrosal nerve (parasympathetic fibres to mucous glands and lacrimal gland)
Nerve to stapedius muscle of inner ear
Chorda tympani (special sensory fibres to anterior 2/3 of tongue and parasympathetic fibres to submandibular and sublingual glands)
what extracranial branches does the facial nerve give rise to after exiting through the stylomastoid Foramen but BEFORE PAROTID GLAND?
first extracranial branch = posterior auricular nerve (motor innervation to muscles around the ear)
Distal to this, motor branches are sent to belly of digastric muscle
Motor branch to the stylohyoid muscle
the main trunk of the facial nerve continues into the parotid gland. What branches does it split into and what do they innervate?
- Temporal branch – innervates frontalis, orbicularis oculi and corrugator supercilli
- Zygomatic branch – Innervates the orbicularis oculi
- Buccal branch – Innervates the orbicularis oris, buccinator and zygomaticus muscles
- Marginal mandibular branch – Innervates the mentalis muscle
- Cervical branch – innervates the platysma
list the motor, sensory and parasympathetic functions of the facial nerve
Motor: innervates muscles of facial expression, the posterior belly of the digastric, the stylohyoid and the stapedius muscles
Sensory: small area around the concha of auricle- posterior auricular nerve, taste sensation to anterior 2/3 of tongue- chorda tympani
Parasympathetic: supplies submandibular and sublingual salivary glands. Also supplies mucosal and lacrimal glands.
describe the origin and course of the vestibulocochlear nerve
Has 2 parts: vestibular and cochlear fibres – both have sensory function.
Vestibular component arises from the vestibular nuclei complex in the pons and medulla.
Cochlear component arises from the ventral and dorsal cochlear nuclei, in the inferior cerebellar peduncle (connects pons and spinal cord)
Both sets of fibres combine in the pons to form the vestibulocochlear nerve. It emerges from the brain at the cerebellopontine angle and exits the cranium via the internal acoustic meatus of the temporal bone.
The nerve splits to form the vestibular and cochlear nerve
what is the function of the vestibular and cochlear nerve?
vestibular: innervates the vestibular system which is responsible for balance
cochlear nerve: travels to cochlea of inner ear and forms the spiral ganglia which is responsible for sense of hearing
Describe what is meant by tinnitus, what causes it and does it ever go away?
Tinnitus: the sensation of ringing, buzzing or whistling in the ear.
It is a manifestation of disease of the middle/inner ear or cochlear component of the 8th nerve. It occurs due to increased awareness of neural activity in the auditory pathways.
Once it starts, it does not go completely away, even if a person experiences complete hearing loss.
describe what is meant by vertigo and list its associated symptoms
Vertigo: the illusion of movement where someone feels like they are spinning or swaying.
It is often associated with nausea, vomiting, pallor, sweating, difficulties walking and nystagmus (rapid involuntary movements of the eye).
what is menière’s disease and what is it characterised by?
Ménière disease is a disorder of the inner ear, characterized by recurrent attacks of vertigo, deafness, tinnitus and a feeling of pressure or fullness in the ears.
what causes menière’s disease what effect does it have and can it be cured?
It is thought to arise from excessive accumulation of endolymphatic fluid which causes distention of the scala media and ruptures the membrane. Resultantly, this causes degeneration of the organ of Corti. Permanent deafness may occur after repeated attacks.
It is a chronic condition that has no cure but can be managed
describe the diagnosis of menière’s disease
o 2 episodes of vertigo o Hearing loss verified by hearing test o Tinnitus or feeling of fullness in ear o Balance test o Rule out other causes using MRI, CT
describe the management of menière’s disease (symptomatic relief, surgical intervention and therapies)
Symptomatic relief using antiemetics and anticholinergics. Having a low sodium diet and using diuretics may help with the excessive endolymph production. —> Some say reducing stress, caffeine intake and smoking may help too.
Surgical intervention: using a shunt to drain the excess fluid, decompression of the endolymphatic sac or entire removal of it.
Therapies: Rehabilitation for balance problems, hearing aid for hearing loss, positive pressure therapy which applies pulses of pressure to middle ear to reduce fluid build-up.
