Anatomy of the human ear and the pathophysiology of noise-induced hearing loss

(A) Schematic representation of ear anatomy. The ear consists of three parts: the outer, middle, and inner ear. The outer and middle ear are separated by the tympanic membrane. Sound waves are transduced through the tympanic membrane to the chain of three tiny bones (the ossicles) in the middle ear cavity, which is attached to the oval window membrane, leading to fluid vibrations in the inner ear. The inner ear is responsible for hearing (cochlea) and balance (vestibule). (B) The cochlea is divided into three fluid-filled membranous tubes coiling around the modiolus: the scala tympani, scala vestibuli, and scala media. The fluid vibrations create a traveling wave along the basilar membrane, in which hair cells generate the electrical signals and pass them to the spiral ganglion cells. (C) High-intensity sound waves travel through the cochlear duct, causing damage to three key functional areas: the organ of Corti, the spiral ganglion neurons, and the stria vascularis. Hair cells, supporting cells, and spiral ganglion neurons go through morphological changes and eventual apoptosis in extreme cases. Loss of tight junctions, malfunction of endothelial cells, and surrounding cell types contribute to the blood-labyrinth barrier disruption. Abbreviations: BLB, blood-labyrinth barrier; IHC, inner hair cell; OHCs, outer hair cells; SCs, supporting cells; SM, scala media; ST, scala tympani; SV, scala vestibuli. (Source: Xu K, Xu B, Gu J, Wang X, Yu D, Chen Y. Intrinsic mechanism and pharmacologic treatments of noise-induced hearing loss. Theranostics 2023;13[11]:3524-9. Creative Commons Attribution 4.0 International [CC BY 4.0] license, creativecommons.org/licenses/by/4.0.)