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Power amplification in the mammalian cochlea
Andrei N Lukashkin1, Mark N Walling, Ian J Russell
1School of Life Sciences, University of Sussex, Falmer, Brighton, UK. a.lukashkin@sussex.ac.uk
Current Biology : CB
|July 31, 2007
Summary
Scientists directly demonstrated energy production in the mammalian cochlea. This finding provides the first direct evidence of the cochlear amplifier, a mechanism crucial for hearing sensitivity and frequency selectivity.
Area of Science:
- Auditory Neuroscience
- Bioacoustics
- Mechanobiology
Background:
- The mammalian cochlea's sensitivity is attributed to the cochlear amplifier, an active process.
- This amplifier is hypothesized to counteract damping via negative damping, augmenting sound-induced vibrations.
- Previous evidence was indirect, relying on comparative cochlear responses, otoacoustic emissions, and modeling.
Purpose of the Study:
- To provide direct evidence for power amplification in the mammalian cochlea.
- To demonstrate energy production within the cochlea on a cycle-by-cycle basis.
- To validate the role of negative damping in cochlear function.
Main Methods:
- Utilized laser interferometry to measure basilar membrane responses to sound stimulation.
- Analyzed the nonlinear component of these responses in relation to applied forces.
- Investigated active processes within the cochlea at a micro-level.
Main Results:
- Demonstrated that energy is actively produced in the cochlea.
- Showed that the nonlinear component of basilar membrane motion leads the acting forces.
- Confirmed that this leading phase relationship is characteristic of active systems with negative damping.
Conclusions:
- Provides the first direct evidence of power amplification in the mammalian cochlea.
- Confirms the existence and function of the cochlear amplifier.
- Challenges and potentially supersedes hypotheses of cochlear function not based on negative damping.
Related Concept Videos
01:13The 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.
01:22Hair 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.
01:15Auditory 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...
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01:16Anatomy of the Ear
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01:31Hearing
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.
01:21Perceiving Loudness, Pitch, and Location
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Place theory, or place coding, suggests that different pitches are heard because various sound waves activate specific locations along the cochlea's basilar membrane. The brain determines the pitch of a sound by identifying...
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