FIGURE 1 | Anatomy of the auditory system, membranous labyrinth, and sensory epithelia.

a | Diagrammatic cross-section through the human head illustrating the three (outer, middle and inner) regions of the auditory system. The outer ear is comprised of the pinna and external auditory meatus, and is bounded on its medial side by the tympanic membrane. The middle ear is an air-filled space containing the three auditory ossicles bounded by the tympanic membrane and the round and oval windows. The third ossicle, the stapes, covers the oval window. The inner ear is comprised of the membranous labyrinth (blue), which is surrounded by a bony labyrinth and innervated by the VIIIth (statoacoustic) cranial nerve. b | The isolated membranous labyrinth, endolymphatic duct and statoacoustic ganglion. The membranous labyrinth is comprised of a dorsal, vestibular portion that mediates the senses of balance and acceleration, and a ventral, auditory region that mediates the sense of hearing. c | Cross-section through one of the canal cristae, illustrating the raised sensory epithelium. A layer of mechanosensory hair cells (HC) is located at the lumenal surface with a layer of non-sensory supporting cells (SC) located adjacent to the basement membrane (BM). d | Cross-section through the utricular macula (sensory epithelium). The structure is similar to that of the cristae, with a lumenal layer of hair cells located above basally located supporting cells. In addition, in the utricular and saccular maculae, hair cell stereociliary bundles project into an otoconial membrane (OM) that also contains otoconia (OT). e | Cross-section through the cochlear duct, illustrating the sensory epithelium (the organ of Corti; boxed region) and the associated spiral ganglion neurons. As in the utricular macula, the hair cells in the organ of Corti are covered by a gelatinous membrane referred to as the tectorial membrane.

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