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Otology
Published in Adnan Darr, Karan Jolly, Jameel Muzaffar, ENT Vivas, 2023
Jameel Muzaffar, Chloe Swords, Adnan Darr, Karan Jolly, Manohar Bance, Sanjiv Bhimrao
Acoustic reflex: Stapedius muscle in middle ear contracts in response to an intense sound Crossed vs uncrossedCN VIII > cochlear nucleus > SOC (bilateral) > FN nucleus (bilateral) > stapediusPattern of abnormality helps identify site of lesionNormal stapedial reflex threshold is 70–100 dB above the pure tone thresholdIf suspect retrocochlear pathology, test acoustic reflex decay: Decreased auditory perception with sustained stimulus
Anatomy and Physiology of Hearing
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
Ananth Vijendren, Peter Valentine
The middle ear acts as an efficient transformer to conduct acoustic energy from the low-impedance high-velocity TM, to the high-impedance, low-velocity fluid-filled cochlea. The impedance difference is mainly matched by the ratio of the surface area of the TM to the stapes footplate (approximately 18:1, or about 25 dB). A much smaller part is played by the lever action of the ossicles. The stapedius muscle plays a role in reflex contraction and stiffening of the ossicular chain to protect the cochlea's sensory epithelium from high-amplitude sounds (see below). In humans, the role of the tensor tympani is unknown, but it does not normally contract in response to sound. Aside from air conduction, the cochlea can also be directly stimulated by vibration of the bony skull (through the bone of the EAC, ossicles or cochlea). The middle ear has a resonant frequency around 1–3 kHz. If this resonance is reduced by a mechanical problem in the ossicular chain (e.g. fixation), the ossicular component of bone conduction is affected and results in a drop in the bone-conduction threshold. This classically appears at 2 kHz as Carhart's notch in the bone-conduction threshold in otosclerosis; however, Carhart's effect may be present between 1 and 4 kHz in any pathology affecting the ossicles.
Head and Neck
Published in Rui Diogo, Drew M. Noden, Christopher M. Smith, Julia Molnar, Julia C. Boughner, Claudia Barrocas, Joana Bruno, Understanding Human Anatomy and Pathology, 2018
Rui Diogo, Drew M. Noden, Christopher M. Smith, Julia Molnar, Julia C. Boughner, Claudia Barrocas, Joana Bruno
The facial nerve (CN VII) follows a complicated course through the temporal bone, giving off several branches (Plate 3.16; described in detail in Section 3.3.1.7). It enters the internal auditory meatus and performs a hairpin turn behind the cochlea. At the anterior point of the turn, the geniculate ganglion is found. This is a sensory ganglion, whose axons carry information from the taste receptors of the anterior tongue and from the skin of the external auditory meatus. A branch of the facial nerve projects anteriorly from the geniculate ganglion, forming the greater petrosal branch of the facial nerve. These fibers emerge from the tegmen tympani of the temporal bone into the middle cranial fossa, and join the deep petrosal nerve to form the nerve of the pterygoid canal (Vidian nerve). They are preganglionic fibers running to the pterygopalatine ganglion. The next branch is the chorda tympani, which passes between the incus and malleus near the tympanic membrane and then exits the temporal bone through the petrotympanic fissure, just posterior to the mandibular fossa, to join the lingual nerve. The third branch goes to the stapedius muscle in the middle ear. The rest of the facial nerve is entirely motor and exits the temporal bone through the stylomastoid foramen.
Maximum acceptable level for the determination of ECAP and ESRT in a paediatric population
Published in Cochlear Implants International, 2022
Federica Di Berardino, Sara Cavicchiolo, Maria del Carmen Fuentes, Alejandra Kontides, Kathrin Lauss, Diego Zanetti
Objective measures such as electrically evoked compound action potentials (ECAPs) and electrically evoked stapedius reflex thresholds (ESRTs) can provide reliable, non-subjective guidance for fitting CIs, functional assessment and for monitoring auditory neural health. ECAP measurements record the compound action potential of the stimulated neurons in the cochlea – the first layer of response to an auditory sensation. The stapedius reflex, as it is described for normal-hearing individuals, is defined as the contraction of the stapedius muscle in the middle ear in response to an intense acoustic stimulus. This muscle contraction results in an attenuation of the acoustic energy, which protects the inner ear. The stapedius reflex arc starts at the auditory nerve fibres, goes via the cochlear nucleus into the brainstem, triggers the facial nerve on both sides, and results in contraction of the stapedius muscle (Mukerji et al., 2010). During ESRT recordings, electrical stimulation is delivered via the CI; once the current is high enough to trigger the stapedius reflex, its occurrence can either be directly observed through the microscope (intraoperatively) or via immittances measurements (postoperatively).
Taste and acoustic reflex after recovery from facial muscle paralysis in patients with facial nerve palsy
Published in Acta Oto-Laryngologica, 2021
Teruyuki Sato, Nobuo Ohta, Youji Tareishi, Takechiyo Yamada
At 6 months after treatment, the number of subjects with normal AR was significantly smaller than the number of subjects with a normal taste. This demonstrates that it is more difficult for AR to recover than it is for taste. The reason for this surmised to lie in the thinness of the nerves in the ear: thin nerve fibers are said to be more resistant to compression and pathological invasion than thick nerve fibers [6,13]. In addition, recovery of nerve damage usually begins in thick nerves [13]. Because the nerve thickness is in the order of facial nerve main trunk > chorda tympani > nerve to stapedius [14], there is the possibility that recovery of the nerve to the stapedius is delayed. Since the stapedius muscle is a striated muscle, the possibility of muscle disuse with prolonged nerve palsy should also be considered. Therefore, since the disuse of the stapedius muscle has a small effect in the early stage of onset, the AR can be used as a prognostic factor for FMP, in which AR appears if nerve damage is weak. However, it is also affected by the disuse of the stapedius muscle in the late stage of onset. It also suggests that AR may not be expressed even if the FNP is restored. These will need to be considered more thoroughly in the future.
Vestibular evoked myogenic potentials: what are they for? An opinion; a hypothesis
Published in Acta Oto-Laryngologica, 2020
The stapedius muscle contracts when there is internal body noise and this changes the vibratory response, which the saccule receives, and makes it different to when there is an external stimulus. The activity of the stapedius muscle is probably much more subtle and complex than is presently recognized by the relatively crude test methods we have, but muscle activity is unlikely to be subtle enough to respond substantially differently to various frequencies of sound. Response is elicited via vestibular efferent activity to neurological endings in the saccule. This changes the stiffness of the otolithic membrane via a kinociliary tonic effect on the otoliths. This is orchestrated via the stereocilia and striated organelle complex [12] and alters the response to vibration from internal sounds, so that these changed external sounds arriving at the macula of the saccule alert the individual to the fact that the stimulus is an external one. The cochlea is specifically sensitized for evaluation of incoming external sound via this macula saccular change rapidly, and also by the antidromic response via the nerve of Oort from the macula of the saccule to the cochlea.