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Related Concept Videos

Hearing01:31

Hearing

When we hear a sound, our nervous system is detecting sound waves—pressure waves of mechanical energy traveling through a medium. The frequency of the wave is perceived as pitch, while the amplitude is perceived as loudness.
Hair Cells01:22

Hair Cells

Hair cells are the sensory receptors of the auditory system—they transduce mechanical sound waves into electrical energy that the nervous system can understand. Hair cells are located in the organ of Corti within the cochlea of the inner ear, between the basilar and tectorial membranes. The actual sensory receptors are called inner hair cells. The outer hair cells serve other functions, such as sound amplification in the cochlea, and are not discussed in detail here.
The Cochlea01:13

The Cochlea

The cochlea is a coiled structure in the inner ear that contains hair cells—the sensory receptors of the auditory system. Sound waves are transmitted to the cochlea by small bones attached to the eardrum called the ossicles, which vibrate the oval window that leads to the inner ear. This causes fluid in the chambers of the cochlea to move, vibrating the basilar membrane.
Anatomy of the Ear01:16

Anatomy of the Ear

Auditory sensation, commonly called hearing, involves the transformation of sonic waves into neural impulses facilitated by the structures of the auditory organ. The prominent, flesh-like structure on the side of the head, called the auricle, directs sound waves towards the auditory canal. The auricle is often mislabeled as the pinna, a term more aligned with mobile structures like a feline's external ear. The auditory canal penetrates the cranium via the external auditory meatus of the...
Auditory Pathway01:15

Auditory Pathway

Auditory pathways constitute the complex neural circuits responsible for transmitting and interpreting auditory information from the peripheral auditory system to the brain. Sound waves are initially captured by the outer ear, funneled through the ear canal, and reach the tympanic membrane (eardrum). These vibrations are transmitted via the middle ear's ossicles to the inner ear's cochlea.
When viewed cross-sectionally, the cochlea reveals the scala vestibuli and scala tympani flanking the...
The Mammary Glands01:12

The Mammary Glands

The female breast is a hemispheric projection of variable size positioned anterior to the pectoralis major and serratus anterior muscles. A fascia layer composed of dense, irregular connective tissue connects it to these muscles.
Each breast features a pigmented projection known as the nipple, through which milk emerges via closely spaced openings of ducts, referred to as lactiferous ducts. Surrounding the nipple is a circular pigmented area of skin named the areola, which appears rough due to...

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In vivo evidence for a cochlear amplifier in the hair-cell bundle of lizards.

Proceedings of the National Academy of Sciences of the United States of America·2001
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Distortion product otoacoustic emissions in the tree frog Hyla cinerea.

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Related Experiment Video

Updated: Jul 15, 2026

Auditory Brainstem Response and Outer Hair Cell Whole-cell Patch Clamp Recording in Postnatal Rats
09:23

Auditory Brainstem Response and Outer Hair Cell Whole-cell Patch Clamp Recording in Postnatal Rats

Published on: May 24, 2018

Evidence for an active process and a cochlear amplifier in nonmammals.

G A Manley1

  • 1Lehrstuhl für Zoologie, Technische Universität München, 85747 Garching, Germany. geoffrey.manley@bio.tum.de

Journal of Neurophysiology
|August 10, 2001
PubMed
Summary

Active processes in sensory hair cells, crucial for hearing sensitivity, likely originated in early fish lateral line systems. These mechanisms, involving hair cell bundles, enhance sound detection across diverse species.

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Area of Science:

  • Auditory Neuroscience
  • Evolutionary Biology
  • Cellular Biophysics

Background:

  • Outer hair cells in mammals exhibit active shape changes, forming a cochlear amplifier that boosts hearing sensitivity and frequency selectivity.
  • Evidence suggests active processes are present in non-mammalian sensory hair cells, prompting investigation into their evolutionary origins and commonality.

Purpose of the Study:

  • To explore the evolutionary ancestry and commonality of active mechanisms in sensory hair cells.
  • To determine the likely origin of active motor mechanisms in the earliest hair cells of the lateral line system.
  • To investigate the location and function of active processes in non-mammalian auditory systems.

Main Methods:

  • Review of existing evidence on active processes in mammalian and non-mammalian sensory hair cells.
  • Comparative analysis of hair cell function across different vertebrate groups.
  • Examination of auditory phenomena in terrestrial non-mammals.

Main Results:

  • Active movements in hair cells are advantageous for signal detection near thermal noise levels and overcoming fluid viscosity.
  • The earliest active motor mechanism is hypothesized to have been localized in the hair-cell bundle of fish lateral line systems.
  • Auditory phenomena in terrestrial non-mammals indicate the presence of a cochlear amplifier, suggesting the mammalian ear is not unique in this regard.

Conclusions:

  • Active processes in sensory hair cells likely evolved early, potentially in the lateral line system of fish.
  • The active motor mechanism is proposed to have originated within the hair-cell bundle.
  • Recent findings support the localization of active processes in non-mammalian hair-cell bundles, closely linked to the transduction process.