Hasil (
Bahasa Indonesia) 1:
[Salinan]Disalin!
The cochlea also mounts a significant inflammatory response following noiseexposure. Infiltration of inflammatory cells including macrophages as well asactivation of inherent macrophages in the cochlea occurs in the period after acutenoise exposure18. Whilst this inflammatory response is likely part of the reparativeprocesses in the cochlea following noise, it is conceivable that they may exacerbate or contribute to the ongoing injury, especially chronic injury. This needs to be furtherinvestigated.Adaptation to noise—The response of the cochlea to noise exposure is complicatedby the fact that its reaction is not purely “passive” as it clearly adapts to excessivesound exposure (eg. Housley et al.19).Exposure to a non-traumatic noise or to hypoxia provides some protection to the earfrom a subsequent traumatic noise exposure (eg. Canlon and Fransson20). Thisphenomenon, known as sound conditioning may relate to mobilisation of inherentprotective processes, particularly oxidative enzymes and antioxidants.21 Noiseexposure also upregulates the expression of a variety of proteins 22-24 includingprotective (eg Yamamoto et al.25) and repair proteins. The cochlea receives adescending or efferent innervation that arises in the Superior Olivary Complex in thebrainstem and innervates both the OHC and the boutons of the type I neuronsinnervating IHC. Activation of these pathways appears to dampen the cochlearresponse to noise and hence may also provide some “protection” from noise exposure.The role of such a variety of active reactions of the cochlea to excessive soundexposure in the human response to noise exposure has not been established or wellconsidered. However, variations in these across the population could affect thecharacteristic susceptibility of individuals to noise-induced hearing loss.Consequences for tinnitus—Clearly there are considerable pathological changes inthe cochlea that are associated with noise exposure and noise-induced hearing lossthat could underly the tinnitus observed after noise. The changes to the hair cells,neurons and supporting structures will lead to significant alterations in functionalinput to the central nervous system and alter the pattern of driven and standingactivity in central auditory nuclei. Many of the functional changes in the centralauditory pathways following noise exposure have been well characterised (egcochlear nucleus, inferior colliculus and cortex) and will be discussed by others in thissymposium. However, mostly these central changes have been correlated to thesubstantial hair cell and neuronal loss. How injury or loss of some of the supportingand accessory structures such as the lateral wall tissues are manifest centrally has not been established.Important to the consideration of the relationship of cochlear noise-induced injury andtinnitus is that the cochlear pathologies, and indeed the adaptive reaction to noise, are very different among individuals and also show substantial variation with different
noise exposures. There is an implicit assumption that the injury is of hair cell, and to
some extent neuronal origin, but clearly there are many other pathologies which
would not be distinguishable in humans using standard clinical functional assessment
methods such as the pure tone audiogram. The evidence of neuronal injury without
any change in auditory thresholds, in animals, further indicates that the pure tone
audiogram will not provide a suitable index of all cochlear injury.
Injury to the cochlea after noise may also not be static as indicated by the ongoing
degeneration that can occur (eg. Kujawa and Liberman8) and the impact of a
continued inflammatory reaction in the ear from chronic cochlear injury on auditory
function is also not known. Thus it is important to acknowledge that the response of
the cochlea to noise exposure is complicated and varies across individuals. This may
account for substantial differences in the extent to which noise may influence the
generation of tinnitus across individuals.
Author information: Peter R Thorne, Section of Audiology, The University of
Auckland, Auckland, New Zealand
Sedang diterjemahkan, harap tunggu..