Hair Cells

Walter Marcotti, University of Sheffield, Sheffield, United Kingdom
Sergio Masetto, University of Pavia, Pavia, Italy

Published online: January 2010

DOI: 10.1002/9780470015902.a0000181.pub2

Hair cells are the sensory receptors in the inner ear that detect sound and head motion to begin the processes of hearing and balance control. The defining feature of hair cells is the hair bundle, the transduction organelle protruding from their apical surface composed of ordered arrays of stereocilia. Mechanical deflection of the hair bundle, normally induced by physiological stimuli, increases the open probability of mechanically gated cation channels located at the tip of stereocilia. The resulting depolarizing inward current generates a receptor potential. The information encoded in this electrical response is transmitted to the auditory or vestibular afferent nerve fibres via the Ca2+-induced release of neurotransmitter from the hair cell's basal pole. In this way sensory information is relayed to the brain enabling us to perceive sound and maintain balance. In mammals, hair cell loss causes irreversible balance and hearing impairment because these sensory cells show very little or no regenerative ability.

Key concepts:

  • Hair cells are the sensory receptors of both the auditory and vestibular systems in vertebrates.
  • Inner ear hair cells derive their name from the stereocilia that protrude from their apical surface, which are deflected as a result of sound (cochlea) or head movement (vestibular organs) and initiate the sensory transduction process.
  • Cochlear hair cells convert acoustic stimuli into electrical activity that allows the brain to perceive the sensation of hearing.
  • Vestibular hair cells inform the central nervous system of head position and movements.
  • The hair bundle, the defining feature of all hair cells, is the mechano-receptive organelle directly responsible for mechano-transduction, i.e. for converting the natural stimulus into a neural signal.
  • In mammals, hair cell loss due to acoustic over-stimulation, ototoxic drugs, ageing and genetic defects is irreversible, leading to a permanent loss of function.

Keywords: auditory hair cells; vestibular hair cells; inner hair cells; outer hair cells; mechano-transduction

Figure 1. Morphological organization of the inner ear. (a) Different sensory structures of the inner ear. P.C., perilymphatic compartment and E.C., endolymphatic compartment. (b)–(d) Sensory neuroepithelia and accessory structures present in the semicircular canals (b), otolith organs (c) and the cochlea (d). Type I and II hair cells are found in the cristae and maculae; inner (IHCs) and outer (OHCs) hair cells are found in the organ of Corti. In the semicircular canals, the stereocilia are embedded in a gelatinous material called the cupula (b). Movement of the cupula, as a consequence of head rotation (white arrow), results in stereociliar deflection. In the saccule and utricle, the tips of the stereocilia are embedded in the otolith membrane (c), note the presence of several small pebbles called otoliths made of calcium carbonate and proteins. Otolith movement produced by vertical or horizontal head accelerations (white arrows) displaces the otolith membrane, which deflects the stereocilia. In the cochlea (d), sound-induced vibration of the basilar membrane causes a shear force between the tectorial membrane and the inner and outer hair cells, resulting in hair bundle displacement. For clarity, only one afferent or efferent fibre is shown to contact an IHC and OHC. This composite figure has been partially redrawn and reprinted with permission from Hennig Arzneimittel GmbH & Co. KG, Wiesbaden, Germany (www.hennig-arzneimittel.de).
Figure 2. Schematic diagram of the adult mammalian vestibular neuroepithelium. Two Type II hair cells (II), one Type I hair cell (I), three supporting cells (S.C.), afferent (Aff., red) and efferent (Eff., light blue) nerve fibres are shown. Type II hair cells are contacted by bouton terminals whereas the Type I cell's basolateral membrane is enveloped by the calyx terminal. Synaptic vesicles containing the neurotransmitter (glutamate) and the efferent neurotransmitter (acetylcholine) are also shown. Presynaptic vesicles in hair cells are shown tethered to the synaptic body (ribbon). For simplicity, only few afferent terminals are shown that face the presynaptic ribbons. The efferent synapse onto Type II hair cell is marked by a subsynaptic cistern (c.). An outer face (o.f.) synapse between the Type II hair cell and the calyx is also shown. The apical surface of hair cells is characterized by the hair bundle, whereas supporting cells have short microvilli. Only supporting cells contact the basement membrane. Below the basement membrane afferent nerve fibres become coated by the myelin sheath.
Figure 3. Myosin-mediated mechano-transducer adaptation. In the absence of stimuli the stereocilia are in their resting position, where approximately 15% of the mechano-sensitive (MET) channels are open. For simplicity, only two stereocilia per bundle are shown. During an excitatory stimulus (gray arrow), stereocilia deflection produces an increase in tension of the rigid tip links, which pull down the MET channels. Sliding of the MET channel stretches a still unidentified elastic component (gating spring) connecting the MET channel and the myosin-1c protein. The interaction of the myosin-1c with the actin filaments inside the stereocilia is Ca2+/calmodulin-dependent. Stretching of the gating spring results in the opening of MET channels. The influx of Ca2+ ions into the stereocilia causes myosin-1c to slip down the actin cytoskeleton. This reduces tension at the gating spring and permits the MET channel closure (adaptation). As Ca2+ is removed by the stereocilia, mainly by Ca2+ pumps located in the stereocilia membrane (not shown), myosin-1c rebinds to the actin filament, although at a lower point. This interaction is able to exert sufficient tension on the gating spring to restore the normal (resting) sensitivity. At the end of the stimulus, while the hair bundle returns to its resting position, myosin-1c climbs along the actin filament to restore the normal sensitivity. This is a generally accepted model of adaptation, which is based on the assumption that the MET channels are located at the top of the tip link (e.g. on the taller stereocilia; for a review see: LeMasurier and Gillespie (2005). However, recent findings using fast Ca2+ imaging have shown that the MET channel is likely to be located at the bottom of the tip link (on the shorter stereocilia), questioning the above mechanism (Beurg et al., 2009).
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 References
    Beurg M, Fettiplace R, Nam JH and Ricci AJ (2009) Localization of inner hair cell mechanotransducer channels using high-speed calcium imaging. Nature Neuroscience 12(5): 553–558.
    Brown SD, Hardisty-Hughes RE and Mburu P (2008) Quiet as a mouse: dissecting the molecular and genetic basis of hearing. Nature Review. Genetics 9: 277–290.
    Brownell WE, Bader CR, Bertrand D and de Ribaupierre Y (1985) Evoked mechanical responses of isolated cochlear outer hair cells. Science 227(4683): 194–196.
    book Brownell WE (2006) "The piezoelectric outer hair cells". In: Eatock RA, Fay RR and Popper AN (eds) Vertebrate Hair Cells, pp. 313–347. New York: Springer.
    Chan DK and Hudspeth AJ (2005) Mechanical responses of the organ of Corti to acoustic and electrical stimulation in vitro. Biophysical Journal 89(6): 4382–4395.
    Collado MS, Burns JC, Hu Z and Corwin JT (2008) Recent advances in hair cell regeneration research. Current Opinion in Otolaryngology & Head and Neck Surgery 16(5): 465–471.
    Correia MJ and Lang DG (1990) An electrophysiological comparison of solitary type I and type II vestibular hair cells. Neuroscience Letters 116: 106–111.
    Eatock RA (2000) Adaptation in hair cells. Annual Review of Neuroscience 23: 285–314.
    Eatock RA and Hurley KM (2003a) Functional development of hair cells. Current Topics in Developmental Biology 57: 389–448.
    book Eatock RA and Hurley KM (2003b) "Functional development of hair cells". In: Romand R and Varela-Nieto I (eds) Development of the Auditory and Vestibular Systems, 3, Molecular Development of the Inner Ear, pp. 348–442. San Diego: Academic Press.
    book Eatock RA and Lysakowski A (2006) "Mammalian vestibular hair cells". In: Eatock RA, Fay RR and Popper AN (eds) Vertebrate Hair Cells, pp. 348–442. New York: Springer.
    Fettiplace R and Hackney CM (2006) The sensory and motor roles of auditory hair cells. Nature Review. Neuroscience 7(1): 19–29.
    Fuchs PA (2005) Time and intensity coding at the hair cell's ribbon synapse. Journal of Physiology 566(part 1): 7–12.
    book Furness DN and Hackney CM (2006) "The structure and composition of the stereociliary bundle of vertebrate hair cells". In: Eatock RA, Fay RR and Popper AN (eds) Vertebrate Hair Cells, pp. 95–153. New York: Springer.
    Géléoc GS, Risner JR and Holt JR (2004) Developmental acquisition of voltage-dependent conductances and sensory signaling in hair cells of the embryonic mouse inner ear. Journal of Neuroscience 24(49): 11148–11159.
    Glowatzki E, Grant L and Fuchs P (2008) Hair cell afferent synapses. Current Opinion in Neurobiology 18(4): 389–395.
    Goldberg JM (2000) Afferent diversity and the organization of central vestibular pathways. Experimental Brain Research 130(3): 277–297.
    book Goodyear RJ, Kros CJ and Richardson GP (2006) "The development of hair cells in inner ear". In: Eatock RA, Fay RR and Popper AN (eds) Vertebrate Hair Cells, pp. 20–94. New York: Springer.
    Goodyear RJ, Marcotti W, Kros CJ and Richardson GP (2005) Development and properties of stereociliary link types in hair cells of the mouse cochlea. Journal of Comparative Neurolology 485(1): 75–85.
    Housley GD, Marcotti W, Navaratnam D and Yamoah EN (2006) Hair cells – beyond the transducer. Journal of Membrane Biology 209(2-3): 89–118.
    Izumikawa M, Minoda R, Kawamoto K et al. (2005) Auditory hair cell replacement and hearing improvement by Atoh1 gene therapy in deaf mammals. Nature Medicine 11(3): 271–276.
    Jahn R, Lang T and Sudhof TC (2003) Membrane fusion. Cell 112: 519–533.
    Johnson SL, Marcotti W and Kros CJ (2005) Increase in efficiency and reduction in Ca2+ dependence of exocytosis during development of mouse inner hair cells. Journal of Physiology 563(part 1): 177–191.
    Kennedy HJ, Crawford AC and Fettiplace R (2005) Force generation by mammalian hair bundles supports a role in cochlear amplification. Nature 433: 880–883.
    LeMasurier M and Gillespie PG (2005) Hair-cell mechanotransduction and cochlear amplification. Neuron 48(3): 403–415.
    Liberman MC (1982) The cochlear frequency map for the cat: labeling auditory-nerve fibers of known characteristic frequency. Journal of the Acoustical Society of America 72(5): 1441–1449.
    Lysakowski A and Goldberg JM (2008) Ultrastructural analysis of the cristae ampullares in the squirrel monkey (Saimiri sciureus). Journal of Comparative Neurology 511(1): 47–64.
    Masetto S and Correia MJ (1997) Electrophysiological properties of vestibular sensory and supporting cells in the labyrinth slice: before and during regeneration. Journal of Neurophysiology 78: 1913–1927.
    Masetto S, Perin P, Malusà A, Zucca G and Valli P (2000) Membrane properties of chick semicircular canal hair cells in situ during embryonic development. Journal of Neurophysiology 83(5): 2740–2756.
    Meyer AC, Frank T, Khimich D et al. (2009) Tuning of synapse number, structure and function in the cochlea. Nature Neuroscience 12(4): 444–453.
    Moody WJ and Bosma MM (2005) Ion channel development, spontaneous activity, and activity-dependent development in nerve and muscle cells. Physiological Reviews 85(3): 883–941.
    Moser T, Neef A and Khimich D (2006) Mechanisms underlying the temporal precision of sound coding at the inner hair cell ribbon synapse. Journal of Physiology 576(part 1): 55–62.
    Nouvian R, Beutner D, Parsons TD and Moser T (2006) Structure and function of the hair cell ribbon synapse. Journal of Membrane Biology 209(2-3): 153–165.
    book Pickles JO (2008) An Introduction to the Physiology of Hearing, 3rd edn, pp. 25–70. Bingley, UK: Emerald.
    Platzer J, Engel J, Schrott-Fischer A et al. (2000) Congenital deafness and sinoatrial node dysfunction in mice lacking class D L-type Ca2+ channels. Cell 102: 89–97.
    book Pujol R, Lavigne-Rebillard M and Lenoir M (1998) "Development of sensory and neural structures in the mammalian cochlea". In: Rubel EW, Popper AN and Fay RR (eds) Development of the Auditory System, pp. 146–192. New York: Springer.
    Rubel EW, Dew LA and Roberson DW (1995) Mammalian vestibular hair cell regeneration. Science 267(5198): 701–707.
    Rüsch A and Eatock RA (1996) A delayed rectifier conductance in type I hair cells of the mouse utricle. Journal of Neurophysiology 76(2): 995–1004.
    Staecker H, Praetorius M, Baker K and Brough DE (2007) Vestibular hair cell regeneration and restoration of balance function induced by math1 gene transfer. Otology & Neurotology 28(2): 223–231.
    Stauffer EA, Scarborough JD, Hirono M et al. (2005) Fast adaptation in vestibular hair cells requires myosin-1c activity. Neuron 47: 541–553.
    Sterling P and Matthews G (2005) Structure and function of ribbon synapses. Trends in Neuroscience 28(1): 20–29.
    Strassmaier M and Gillespie PG (2002) The hair cell's transduction channel. Current Opinion in Neurobiology 12(4): 380–386.
    Wong WH, Hurley KM and Eatock RA (2004) Differences between the negatively activating potassium conductances of mammalian cochlear and vestibular hair cells. Journal of the Association for Research in Otolaryngology 5(3): 270–284.
    Zheng J, Shen W, He DZ et al. (2000) Prestin is the motor protein of cochlear outer hair cells. Nature 405(6783): 149–155.
 Further Reading
    book Eatock RA, Fay RR and Popper AN (2006) Vertebrate Hair Cells. New York: Springer.
    book Goldberg JM and Fernández C (1984) "The vestibular system". Handbook of Physiology. The Nervous System, pp. 877–1022. Bethesda: American Physiological Society.
    book Harada Y (1988) The Vestibular Organs – S.E.M. Atlas of the Inner Ear. Amsterdam: Kugler & Ghedini Publications.
    book Salvi RJ, Popper AN and Fay RR (2008) Hair Cell Regeneration, Repair, and Protection. New York: Springer.
    book Wilson VJ and Melvill Jones G (1979) Mammalian Vestibular Physiology. New York: Plenum Press.

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Sensory Systems
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Article Title: Hair Cells
 
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Marcotti, Walter, and Masetto, Sergio(Jan 2010) Hair Cells. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000181.pub2]