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Hearing

Tuning in with motor proteins

Nature volume 405, pages 131–133 (2000)Cite this article

The sensory part of the mammalian auditory organ is housed within a coiled tube called the cochlea (Fig. 1a). The hair cells are arranged with exquisite precision within the organ of Corti, a cellular layer that lies on a long, narrow membrane called the basilar membrane ( Fig. 1b). The width and stiffness of the basilar membrane change progressively along the cochlear coil, so that it vibrates best to high- and low-frequency sounds at its base and apex, respectively. This forms a map of incoming sound frequencies that is transmitted to an associated array of auditory nerve fibres. The interaction between vibrations of the basilar membrane and the sensory hair bundles is extremely complex (Fig. 1b). One particularly striking feature of the organ of Corti is that it contains two distinct populations of hair cells. There is a single row of goblet-shaped, conventional, inner hair cells and several rows of cylindrical outer hair cells ( Fig. 1b). Why do mammals need these two types?

The physical properties of the basilar membrane alone cannot account for the known sensitivity and frequency selectivity of the living ear. Sellick et al.2 showed that it is very finely tuned, and Davis3 subsequently described the need for a ‘cochlear amplifier’. The idea that the outer hair cells might be the amplifiers was dramatically reinforced by the finding4 that these cells can change length rapidly when electrically stimulated. The outer hair cells have since been subjected to a whole range of experimental manipulations, leading to a widely accepted explanation for the cellular mechanism5. In this theory, arrays of densely packed, voltage-dependent motor proteins in the membrane of the outer hair cell force the cell's surface area to change. The cell is constrained by a two-dimensional protein skeleton (Fig. 1c ), so that changes in its surface area are expressed as changes in cell length.

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Figure 1: How we hear.

References

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  1. Department of Physiology School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK

    Matthew Holley

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Correspondence to Matthew Holley.

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Holley, M. Tuning in with motor proteins. Nature 405, 131–133 (2000). https://doi.org/10.1038/35012185

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