Hair cell

Jump to: navigation, search
Hair cell
Hair cell - Section through the spiral organ of Corti. Magnified. ("Outer hair cells" labeled near top; "inner hair cells" labeled near center).
Section through the spiral organ of Corti. Magnified. ("Outer hair cells" labeled near top; "inner hair cells" labeled near center).
Location Cochlea
Function Amplify sound waves and transduce auditory information to the Brain Stem
Morphology Unique (see text)
Presynaptic connections None
Postsynaptic connections Via auditory nerve to vestibulocochlear nerve to inferior colliculus
Gray's subject #232 1057

WikiDoc Resources for Hair cell

Articles

Most recent articles on Hair cell

Most cited articles on Hair cell

Review articles on Hair cell

Articles on Hair cell in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Hair cell

Images of Hair cell

Photos of Hair cell

Podcasts & MP3s on Hair cell

Videos on Hair cell

Evidence Based Medicine

Cochrane Collaboration on Hair cell

Bandolier on Hair cell

TRIP on Hair cell

Clinical Trials

Ongoing Trials on Hair cell at Clinical Trials.gov

Trial results on Hair cell

Clinical Trials on Hair cell at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Hair cell

NICE Guidance on Hair cell

NHS PRODIGY Guidance

FDA on Hair cell

CDC on Hair cell

Books

Books on Hair cell

News

Hair cell in the news

Be alerted to news on Hair cell

News trends on Hair cell

Commentary

Blogs on Hair cell

Definitions

Definitions of Hair cell

Patient Resources / Community

Patient resources on Hair cell

Discussion groups on Hair cell

Patient Handouts on Hair cell

Directions to Hospitals Treating Hair cell

Risk calculators and risk factors for Hair cell

Healthcare Provider Resources

Symptoms of Hair cell

Causes & Risk Factors for Hair cell

Diagnostic studies for Hair cell

Treatment of Hair cell

Continuing Medical Education (CME)

CME Programs on Hair cell

International

Hair cell en Espanol

Hair cell en Francais

Business

Hair cell in the Marketplace

Patents on Hair cell

Experimental / Informatics

List of terms related to Hair cell


Hair cells are the sensory receptors of both the auditory system and the vestibular system in all vertebrates. In mammals, the auditory hair cells are located within the organ of Corti on a thin basilar membrane in the cochlea of the inner ear. They derive their name from the tufts of stereocilia that protrude from the apical surface of the cell, a structure known as the hair bundle, into the scala media, a fluid-filled tube within the cochlea. Mammalian cochlear hair cells come in two anatomically and functionally distinct types: the outer and inner hair cells. Damage to these hair cells results in decreased hearing sensitivity, i.e. sensorineural hearing loss.

Hair bundles as sound detectors

Research of the past decades has shown that outer hair cells do not send neural signals to the brain, but that they mechanically amplify low-level sound that enters the cochlea. The amplification may be powered by movement of their hair bundles, or by an electrically driven motility of their cell bodies. The inner hair cells transform the sound vibrations in the fluids of the cochlea into electrical signals that are then relayed via the auditory nerve to the auditory brainstem and to the auditory cortex.

Inner hair cells – from sound to nerve signal

The deflection of the hair-cell stereocilia opens mechanically gated ion channels that allow any small, positively charged ions (primarily potassium and calcium) to enter the cell. Unlike many other electrically active cells, the hair cell itself does not fire an action potential. Instead, the influx of positive ions from the endolymph in Scala media depolarizes the cell, resulting in a receptor potential. This receptor potential opens voltage gated calcium channels; calcium ions then enter the cell and trigger the release of neurotransmitters, mainly glutamate, at the basal end of the cell. The neurotransmitters diffuse across the narrow space between the hair cell and a nerve terminal, where they then bind to receptors and thus trigger action potentials in the nerve. In this way, the mechanical sound signal is converted into an electrical nerve signal. The repolarization in the hair cell is done in a special manner. The perilymph in Scala tympani has a very low concentration of positive ions. The electrochemical gradient makes the positive ions flow through channels to the perilymph. Nerve fiber innervation is much more dense for inner hair cells than for outer hair cells. A single inner hair cell is innervated by numerous nerve fibers, whereas a single nerve fiber innervates many outer hair cells. Inner hair cell nerve fibers are also very heavily myelinated, which is contrast to the unmyelinated outer hair cell nerve fibers.

Outer hair cells – acoustical pre-amplifiers

In mammalian outer hair cells, the receptor potential triggers active vibrations of the cell body. This so-called somatic electromotility consists of oscillations of the cell’s length, which occur at the frequency of the incoming sound and in a stable phase relation. Outer hair cells have evolved only in mammals. They have not improved hearing sensitivity, which reaches similarly exquisite values also in other classes of vertebrates. But they have extended the hearing range from ca 11 kHz (maximum in some birds) to ca 200 kHz (maximum in some marine mammals). They have also improved frequency selectivity (frequency discrimination), which is of particular benefit for humans, because it enabled sophisticated speech and music.

The molecular biology of hair cells has seen considerable progress in recent years, with the identification of the motor protein (prestin) that underlies somatic electromotility in the outer hair cells.

Hair-bundle motors

Results in recent years further indicate that mammals apparently also have conserved an evolutionarily earlier type of hair-cell motility. This so-called hair-bundle motility amplifies sound in all non-mammalian land vertebrates. It is effected by the closing mechanism of the mechanical sensory ion channels at the tips of the hair bundles. Thus, the same hair-bundle mechanism that detects sound vibrations also actively “vibrates back” and thereby mechanically amplifies weak incoming sound.

Additional images

References

  • Coffin A, Kelley M, Manley GA, Popper AN. Evolution of sensory hair cells. In: GA Manley, AN Popper, RR Fay. Evolution of the Vertebrate Auditory System, Springer-Verlag, New York 2004, pp 55-94.
  • Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science, 4th ed., pp.590-594. McGraw-Hill, New York (2000). ISBN 0-8385-7701-6
  • Manley GA. Advances and perspectives in the study of the evolution of the vertebrate auditory system. In: GA Manley, AN Popper, RR Fay. Evolution of the Vertebrate Auditory System, Springer-Verlag, New York 2004, pp 360-368.
  • Fettiplace R, Hackney CM (2006). "The sensory and motor roles of auditory hair cells". Nat. Rev. Neurosci. 7 (1): 19–29. doi:10.1038/nrn1828. PMID 16371947.

External links

de:Haarzelle


Linked-in.jpg