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Related Concept Videos

The Cochlea01:13

The Cochlea

45.3K
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.
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Hair Cells01:22

Hair Cells

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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.
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Auditory Pathway01:15

Auditory Pathway

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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...
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Hearing01:31

Hearing

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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.
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Perceiving Loudness, Pitch, and Location01:21

Perceiving Loudness, Pitch, and Location

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The human brain perceives pitch through two primary mechanisms reflected in place theory and frequency theory. Each mechanism describes how sound waves are interpreted as specific pitches by the brain, offering insights into the intricate processes of auditory perception.
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...
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Anatomy of the Ear01:16

Anatomy of the Ear

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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...
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Related Experiment Video

Updated: Jul 29, 2025

Morphological and Functional Evaluation of Ribbon Synapses at Specific Frequency Regions of the Mouse Cochlea
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Morphological and Functional Evaluation of Ribbon Synapses at Specific Frequency Regions of the Mouse Cochlea

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Cochlear synaptopathy impairs suprathreshold tone-in-noise coding in the cochlear nucleus.

A Hockley1,2, L R Cassinotti1, M Selesko1

  • 1Kresge Hearing Research Institute, Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA.

The Journal of Physiology
|May 22, 2023
PubMed
Summary
This summary is machine-generated.

Cochlear synaptopathy, damage to auditory nerve synapses, causes difficulties hearing speech in noise, especially for older adults. This study shows synaptopathy disrupts processing of sounds above detection threshold in the cochlear nucleus, impacting speech comprehension.

Keywords:
auditory neurophysiologycentral auditory systemcochlear nucleuselectrophysiologysmall cell cap

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Area of Science:

  • Neuroscience
  • Auditory Neuroscience
  • Otoacoustic Emissions

Background:

  • Hearing impairment can occur without elevated hearing thresholds due to damage to auditory nerve fiber synapses.
  • Cochlear synaptopathy leads to suprathreshold deficits, particularly affecting conversational speech in older individuals.
  • Listening in noise presents challenges for the aging population, motivating research into the underlying neural mechanisms.

Purpose of the Study:

  • To investigate the effects of cochlear synaptopathy on tone-in-noise coding in cochlear nucleus neurons.
  • To determine if synaptopathy impacts the central auditory system's ability to process sounds in noisy environments.

Main Methods:

  • Guinea pigs were exposed to sound overexposure to induce unilateral cochlear synaptopathy.
  • Auditory brainstem response (ABR) wave I amplitudes and auditory nerve synapse integrity were assessed.
  • Single-unit responses from ventral cochlear nucleus neurons were recorded in response to pure-tone and noise stimuli.

Main Results:

  • While tone-in-noise detection thresholds remained unaffected, synaptopathy reduced neural responses to suprathreshold tones in background noise.
  • These suprathreshold deficits were particularly evident in small cells and primary-like neurons within the cochlear nucleus.
  • Quantified cochlear synapse damage correlated with disrupted suprathreshold tone-in-noise coding.

Conclusions:

  • Cochlear synaptopathy causes suprathreshold deficits in tone-in-noise processing within the cochlear nucleus, the auditory brain's first neural station.
  • These findings provide insights into the mechanisms behind difficulties hearing in noisy environments.
  • The cochlear nucleus presents a potential target for assessing and treating listening-in-noise deficits in humans.