Hearing Loss: Does Gender Play a Role?

Authors and Disclosures

Dr. Murphy is a Resident in the Department of Otolaryngology/Head and Neck Surgery, University of Washington Medical Center, Seattle, Wash. Dr. Gates is Professor and Chief, Otology/Neurotology, University of Washington Medical Center, and Director, Virginia Merrill Bloedel Hearing Research Center, Seattle.

Murphy MP, Gates GA. Hearing Loss: Does Gender Play a Role? MedGenMed 1(2), 1999. [formerly published in Medscape Women's Health eJournal 2(5), 1997]. Available at: https://www.medscape.com/viewarticle/408872.

Sidebar: The Cochlea - Anatomy and Physiology

Overview. The cochlea is a spiral tube of about 2 1/2 turns, shaped like the shell of a snail. Its apex is directed anterolaterally, and its base lies against the lateral end of the internal acoustic meatus. The spiral lamina and the cochlear duct separate the anterior part of the cochlea--the scala vestibuli--from the posterior part--the scala tympani (Fig. 1A). The scalae vestibuli and tympani contain perilymph, a fluid similar to extracellular and cerebrospinal fluid, with a K⁺ concentration of 4mEq/L and an Na⁺ concentration of 139mEq/L.

The cochlear duct. The cochlear duct extends from the osseous spiral lamina to the wall of the cochlea (Fig. 1B). Its roof is formed by the vestibular (Reissner's) membrane, which separates it from the scala vestibuli. Its floor is formed by the osseous spiral lamina and the basilar membrane, which separate the cochlear duct from the scala tympani.

Figure 1A. The ear has 3 parts. Conductive hearing loss usually due to problems in external ear; sensorineural hearing loss usually results from middle- or inner-ear disorders.

Figure 1B. High-frequency sounds cause basilar membrane near base of cochlear duct to vibrate; low-frequency sounds vibrate membrane at apex of the cochlear duct.

Figure 1C. Organ of Corti rests on basilar membrane within cochlear duct.

Figure 1D. Organ of Corti contains receptor cells for hearing.

The wall of the cochlear duct is lined by a heavily vascularized, stratified epithelium called the stria vascularis.The stria vascularis produces endolymph, the fluid in the cochlear duct. Endolymph is an intracellular-like fluid with a K⁺ concentration of 144mEq/L and an Na⁺ concentration of 13mEq/L. A DC potential of 80 to 100mv is created by the stria vascularis and Na⁺/K⁺ ATP-ase pumps located in specialized cells in the cochlear duct. Thus, the stria vascularis is the energy source that powers the cochlea and makes hearing possible.

The organ of Corti. Within the cochlear duct is the spiral Organ of Corti, which contains the receptor cell for hearing (Fig. 1C,D). The spiral organ of Corti rests on the basilar membrane. Although the spiral organ is very complex, it is simply conceptualized as comprising 2 types of cells: neuroepithelial hair cells and supporting cells.

The neuroepithelial hair cells are composed of inner type I and outer type II cells. The inner hair cells are arranged in a single row and remain free to respond to movement of endolymph in the cochlear duct. The outer hair cells are arranged in 3 rows in the basal coil of the cochlea and gradually increase to 5 rows in the apical coil. The stereocilia of the outer hair cells are embedded in the overlying gelatinous tectorial membrane.

The perilymph fluid wave causes a frequency-specific movement of the basilar membrane. This results in excitation of the corresponding hair cells and the generation of a cochlear nerve impulse. Thus, the hair cells play a major role in the conversion of mechanical (acoustic) energy into electrical (neural) energy. Hair-cell loss and regeneration is currently an area of active investigation.