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Ear
External, middle, internal ear
Term | Definition |
---|---|
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 |