Скачать или смотреть Inner Ear Anatomy | Chapter 43 – Gray’s Anatomy (42nd)

This chapter provides a detailed anatomical and physiological overview of the inner ear, which houses the sensory organs for both hearing and balance within the complex series of interlinked cavities known as the labyrinth. This structure includes the outer osseous labyrinth and the internal membranous labyrinth. Key to its function are the two specialized fluids: perilymph, which has an ionic composition similar to other extracellular fluids (high sodium, low potassium), and endolymph, which is rich in potassium ions, resembling cytosol. This unique environment maintains the potent endolymphatic potential, especially within the cochlea, which is essential for the extreme sensitivity of the mechanosensory hair cells that convert mechanical vibrations into electrical signals. The organs of balance (vestibular system) consist of the utricle and saccule, which contain the maculae for detecting static balance and linear acceleration, and the three semicircular ducts, which detect angular acceleration via the cristae located in their ampullae. The maculae utilize the inertia of embedded calcium carbonate crystals called otoconia within the otolithic membrane to signal movement. The hair cells rely on tip links to open transduction channels (TMC1) when their stereocilia are deflected, causing depolarization. The organ of hearing is the cochlea, a spiral channel divided into three sections: the perilymph-filled scala vestibuli and scala tympani, and the endolymph-filled cochlear duct. The sensory epithelium for hearing, the organ of Corti, sits on the basilar membrane and features inner hair cells (the main signal producers) and outer hair cells. Sound vibrations generate a traveling wave along the basilar membrane, tuned tonotopically so that high frequencies stimulate the base and low frequencies stimulate the apex. Crucially, the outer hair cells exhibit motility, utilizing the protein prestin to generate forces that boost the basilar membrane movement, enhancing frequency discrimination through cochlear amplification. Afferent information travels via the vestibulocochlear nerve (CN VIII), originating from bipolar neurons located in the vestibular ganglion (Scarpa’s ganglion) and the spiral ganglion (cochlea). Clinically relevant conditions, such as Ménière’s disease (associated with endolymphatic hydrops) and Benign Paroxysmal Positional Vertigo (BPPV), reflect inner ear pathology. Modern treatments for severe sensorineural hearing loss include cochlear implants, which electrically stimulate the remaining spiral ganglion neurons.

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