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Ear

External, middle, internal ear

TermDefinition
What are the components of the external ear? Auricle/pinna, EAM
What is the structure of the pinna? Elastic cartilage covered by skin -> anterior tragus w/ posterior concha, helix outer edge, inferior lobule of fibrofatty tissue
What is the structure of the ear canal? EAM -> tympanic membrane, skin w/ hair and ceruminous glands (wax secretion), lateral 1/3 -> cartilage but deficient posterosuperiorly (fibrous tissue), medial 2/3 -> bony
What is the external ear cutaneous innervation? Cervical plexus great auricular nerve -> C2/3 fibres (inferior/posterior), cervical plexus lesser occipital nerve -> C2/3 fibres (superior), CN Vc -> auriculotemporal (tragus), CN VII -> nervus intermedius (concha), CN X auricular (concha)
What are the components of the middle ear? Tympanic cavity, ossicles, Eustachian tube
What are the boundaries of the tympanic cavity? Roof -> bone plate separating from MCF/meninges/temporal lobe, floor -> bone plate separating from jugular fossa, lateral -> tympanic membrane, medial -> oval window (internal ear)/promontory (bulge from cochlea 1st turn), CN VII posteriorly
What is the structure of the tympanic membrane? Concave lateral surface, malleus handle attached to medial surface, fibrocartilage annulus, cone of light
What are the function of ossicles? Transmit membrane vibrations to internal ear
What is the external ear developed from? 1st pharyngeal cleft -> EAM
What is the middle ear developed from? 1st pharyngeal pouch -> tympanic cavity/Eustachian tube, 1st pharyngeal arch mandibular NCCs -> malleus/short limb of incus, 2nd pharyngeal arch NCCs -> long limb of incus/stapes
What is the internal ear developed from? Otic placode -> cochlear/vestibular ganglia neurons
What are the ossicles? Malleus, incus, stapes
What is the structure of the malleus? Lateral process w/ handle (tympanic membrane), rounded superior head (incus body), tensor tympani muscle (CN Vc)
What is the function of the tensor tympani muscle? CN Vc -> modify sound wave transmission (dampen loud vibrations) by pulling malleus away from tympanic membrane -> prevent hyperacusis, arises from Eustachian tube cartilage -> attached to malleus
What is the structure of the incus? Long process -> articulates w/ stapes
What is the structure of the stapes? Base/footplate sits in oval window (fenestra vestibuli) -> base mvmt causes internal ear fluid vibration, stapedius (CN VII)
What is the function of the stapedius muscle? CN VII -> modify sound wave transmission (dampen loud vibrations) by stabilising stapes and preventing xcs mvmt -> prevent hyperacusis
What is the location and structure of the Eustachian tube? Ant wall of middle ear tympanic cavity -> lateral wall of nasopharynx, medial cartilaginous, lateral bony, lined w mucus membrane
What is the function of the Eustachian tube? Opens during swallowing/yawning -> allow air to enter/escape middle ear to equalise Pa btwn tympanic cavity/external environment
What is the aditus? Posterior tympanic cavity connection w/ mastoid antrum -> small at birth but enlarges as mastoid process enlarges
What is the blood supply and innervation of the middle ear? Maxillary (ECA) anterior tympanic artery, CN IX tympanic plexus, CN VII runs posteriorly in tympanic cavity before travelling inferiorly through facial canal
What is the structure of the internal ear? Sense organs for hearing/balance -> osseous labyringth -> membranous labyrinth -> vestibular/cochlear labyrinths
What is the structure of the membranous labyrinth? Vestibular labyrinth -> utricle/saccule (static eqbm), 3 semicircular canals (dynamic eqbm), cochlear labyrinth -> cochlea (basement membrane, organ of Corti)
What is the innervation of the internal ear? Special sensory from otic placode -> CN VIII -> cochlear division (organ of Corti spiral ganglia), vestibular division (superior vestibular ganglion -> ant/lat semi-circular canals, inferior vestibular ganglion -> post semi-circular canals, saccule)
What is the cause of acoustic neuroma? Benign intracranial tumour (vestibular Schwannoma) of CN VIII myelin forming cells -> NF2 tumour suppressor gene mutation
What are the symptoms of acoustic neuroma? Gradual hearing loss, feeling of fullness in ear, imbalance/dizziness, tinnitus, tumour spreading -> facial parasthesia, impaired caloric reflex
What are the investigations of acoustic neuroma? CT scan w/ iodinated contrast-> moderate/large size, MRI scan -> differentiate mass from other tumours, Rinne's test -> C = B > A = -ve, Weber's test -> C = BD (middle ear blockage masks background)
What are the surgical approaches for acoustic neuroma? Translabyrinthine -> no cerebellar retraction/manipulation but hearing loss and only for small tumours, retrosigmoid -> hearing preserved and large tumours but cerebellar manipulation
Created by: vykleung
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