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Case 2.12
Published in Monica Fawzy, Plastic Surgery Vivas for the FRCS(Plast), 2023
What about formation of the inner ear?This starts in the 4th week and has a different embryological origin to the external ear. This is why hearing loss tends to be conductive rather than a mixed picture of conductive and sensorineural loss.Two otic placodes appear as thickenings lateral to the hindbrain that invaginate to form a pit, then close to form a cyst-which then forms the utricle, saccule, semi-circular canals, and cochlea.The bony labyrinth is formed from the mesenchyme surrounding the inner ear.An invagination of the first branchial groove, called the tubo-tympanic recess, forms the auditory tube and tympanic cavity.Finally: Meckel’s cartilage, from the first arch, forms the malleus and incus, and Reichert’s cartilage forms the stapes.
Anatomy and Physiology of Balance
Published in R James A England, Eamon Shamil, Rajeev Mathew, Manohar Bance, Pavol Surda, Jemy Jose, Omar Hilmi, Adam J Donne, Scott-Brown's Essential Otorhinolaryngology, 2022
Nishchay Mehta, Andrew Forge, Jonathan Gale
The bony labyrinth lies within the petrous temporal bone, which is the densest bone in the body. The bony labyrinth (otic capsule) has three main components: the cochlea (anteriorly), vestibule (centrally), and semicircular canals (posteriorly) (Figure 2.1).
Cranial Neuropathies I, V, and VII–XII
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
The vestibulocochlear nerve is a special somatic afferent nerve consisting of two functional divisions: the vestibular nerve, mediating equilibrium and balance information from the vestibular apparatus (semicircular canals, saccule, and utricle), and the cochlear nerve, mediating auditory information from the cochlear apparatus (organ of Corti in the spiral ganglion). Both of these structures are in the inner ear, which is located deep in the temporal bone within a space called the bony labyrinth (Figure 21.13). The bony labyrinth contains the membranous labyrinth and is filled with perilymph, a fluid with a chemical content similar to that of CSF and plasma. The membranous labyrinth is filled with endolymph, a highly specialized fluid with high protein content. The membranous labyrinth is further divided in two portions: vestibular and cochlear. The hair cells are the sensory receptors for both the vestibular and the cochlear systems.2
Effects of basilar-membrane lesions on dynamic responses of the middle ear
Published in Acta Oto-Laryngologica, 2023
Junyi Liang, Wen Xie, Wenjuan Yao, Maoli Duan
The connection between the ligament in the middle ear and the temporal bone was set as a fixed end constraint.The connection between the outer margin of the ring ligament of the tympanic membrane and the external auditory canal was defined as a fixed-end constraint.The Eardrum, basilar membrane, osseous spiral lamina and inwall of scala vestibuli and scala tympaniare were defined as fluid-structure coupling interfaces.The displacement of the outer margin of oval window and the round window was limited in X and Y direction.The inner ear bony labyrinth wall was set as the rigid wall.
Skew Deviation
Published in Journal of Binocular Vision and Ocular Motility, 2022
Cranial nerve VIII is formed by tracts of fibers originating from each of the structures of the vestibular organs along with the auditory fibers from the cochlea that exit the bony labyrinth through the acoustic meatus along with the facial nerve. CNVIII enters the brainstem at the ponto-medullary junction, the vestibular fibers then projecting to the ipsilateral vestibular nucleus complex (VN) in the lower pons at the level of the fourth ventricle. After leaving the VN, ascending fibers for vertical movement cross over at the level of the CN VI nucleus to travel the contralateral medial longitudinal fasciculus (MLF) to the nuclei of CNs IV and III, and on to the interstitial nucleus of Cajal (INC) and rostral interstitial medial longitudinal fasciculus (riMLF). This portion of the tract carries vestibular afferent fibers, those responsible for transmission of sensory input (Figure 2).
Bilateral asynchronous sudden sensorineural hearing loss and bilateral superior semicircular canal dehiscence*
Published in Hearing, Balance and Communication, 2018
SSCD syndrome was described by Minor et al. [1] in 1998. The bony labyrinth has two openings, the oval and round windows, to allow for the transmission of sound pressure waves from the middle to the inner ear. The presence of a dehiscence in the bone overlying the membranous SSCC creates a third window, giving rise to: auditory and/or vestibular symptoms, such as hearing loss (most commonly low-frequency conductive or mixed with normal tympanograms and acoustic reflex thresholds), autophony, hyperacusis, aural fullness, tinnitus, imbalance, sound-induced vertigo (Tullio phenomenon), middle ear pressure- or intracranial pressure-induced vertigo (Hennebert sign), and oscillopsia [1–3]. The prevalence of SSCD is estimated to be ∼0.5–0.6%, with an additional 1–2% of the population having a very thin layer of bone overlying the canal. However, not all persons with complete or partial SSCD experience symptoms [3,4].