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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
Eighty percent of these efferent fibres synapse directly with OHCs, with the remainder terminating on afferent nerve fibres. The ratio of efferent to afferent fibres in the OHC is 1:2, whereas those in the IHCs is 1:7. This suggests efferent function is mainly to biologically amplify sound, modulate signals (protective damping of loud sounds), and frequency selectivity, via the OHCs. The medial system innervates both ears while the lateral system supplies only the ipsilateral cochlea. Both project to the different parts of the ventral cochlear nucleus.
Physiology of Hearing
Published in John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed, Paediatrics, The Ear, Skull Base, 2018
Soumit Dasgupta, Michael Maslin
The ratio of efferent to afferent fibres in the OHC is 1:2 whereas those in the IHCs is 1:7,111 suggesting that the biological amplifiers are the main substrates of efferent function which in turn inherently implies that the signal modulation is primarily a function of the OHC. The medial system innervates both ears while the lateral system supplies only the ipsilateral cochlea. Both project to the different parts of the ventral cochlear nucleus.
Hearing impairment prevalence and risk factors among adults in rural China: a population-based cross-sectional study
Published in Postgraduate Medicine, 2021
Dong Yang, Jie Liu, Qiaoxia Yang, Qiuxing Lin, Xin Zhang, Mingxin Wang, Xin Li, Jun Tu, Jinghua Wang, Xianjia Ning
Some previous studies have reported the absence of significant sex-related differences in HI prevalence [10,15], while others have indicated that, in older adults, the risk of HI is higher among men than among women [23–25]. Similar to the latter studies, our study showed that HI prevalence, among men, was significantly higher than among women. The specific mechanism for this apparent sex-related difference has not been fully elucidated. However, a previous mouse experiment indicated that ovarian hormones negatively affect the anterior ventral cochlear nucleus, while androgens have a beneficial effect on the structure [26]. Therefore, in older individuals, the negative effects of estrogen, in women, are weakened and the protective effects in men are also decreased. Thus, among older adults, these changes may partly explain the higher prevalence of HI among men than among women.
Larger tumor size and female gender suggest better tinnitus prognosis after surgical treatment in vestibular schwannoma patients with tinnitus
Published in Acta Oto-Laryngologica, 2020
Wei Cao, Zhaohui Hou, Fangyuan Wang, Qingqing Jiang, Weidong Shen, Shiming Yang
Over the past decade, numerous studies have converged to support the hypothesis that the DCN may be an important brain center in the generation and modulation of tinnitus [12]. Animal models have demonstrated that tinnitus is a pathology of dysfunctional excitability in the central auditory system, in particular in the dorsal cochlear nucleus (DCN) of the brainstem [9]. Long-term potentiation (LTP) at DCN multisensory synapses were found in hearing loss and tinnitus caused by acoustic over-exposure. DCN could convey already-formed neural patterns representing tinnitus to higher auditory nuclei such as auditory cortex [13]. Electrical stimulation of the DCN suppressed behavioral evidence of tinnitus, especially at high frequencies. DCN may be a target to suppress tinnitus through a bottom-up neuromodulation approach [12]. Researches on humans brainstem function had shown that wave III and wave V which originated from the ventral cochlear nucleus (VCN), components of auditory brainstem response, reflected a disproportionately high activity at a given peripheral input in human tinnitus subjects [14].
A different view on the link between tinnitus and cognition; is there a reciprocal link?
Published in International Journal of Neuroscience, 2018
Elham Tavanai, Ghassem Mohammadkhani
Functional magnetic resonance imaging (fMRI), Single-Photon Emission Computed Tomography (SPECT) and positron emission tomography (PET) are imaging techniques that can be used for studying neural activity in the human brain directly. Available functional imaging studies have demonstrated different activation patterns in central auditory system of tinnitus patients. However, these differences might be due to differences in patient samples and study methods. Generally, result from these studies suggest abnormal structural and functional changes in tinnitus patients at several levels of brain [37]. Accordingly, in tinnitus sufferer, changes in neuronal excitability have been reported in the dorsal cochlear nucleus (DCN) [31,33,34], ventral cochlear nucleus (VCN) [6,22], inferior colliculus (IC) [5], medial geniculate body (MGB) [38], core and belt regions of auditory cortex [3,38], as well as several non-auditory regions [1–7]. In other words, tinnitus not only change the auditory pathways but also involve some of non-auditory brain regions [1–7].