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Related Concept Videos

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...
The Auditory Ossicles01:11

The Auditory Ossicles

The auditory ossicles of the middle ear transmit sounds from the air as vibrations to the fluid-filled cochlea. The auditory ossicles consist of two malleus (hammer) bones, two incus (anvil) bones, and two stapes (stirrups), one on each side. These bones develop during the fetal stage and are the ones to ossify first. They are fully mature at birth and do not grow afterward.
The aptly named stapes look very much like a stirrup. The three ossicles are unique to mammals, and each plays a role in...
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.
Convergent Evolution01:54

Convergent Evolution

Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.The structures that arise from convergent evolution are called analogous structures. They are similar in function even if they are dissimilar in structure. Further, structures can be analogous while also...
Echo01:06

Echo

The human ear cannot distinguish between two sources of sound if they happen to reach within a specific time interval, typically 0.1 seconds apart. More than this, and they are perceived as separate sources.
Imagine the sound is reflected back to the ears. Assuming that the source is very close to the human, the difference between hearing the two sounds—the emitted sound and the reflected sound—may be more than the minimum time for perceiving distinct sounds. If this is the case, then the...
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.

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Related Experiment Video

Updated: Jul 3, 2026

Physiological Preparation of Hair Cells from the Sacculus of the American Bullfrog (Rana catesbeiana)
12:07

Physiological Preparation of Hair Cells from the Sacculus of the American Bullfrog (Rana catesbeiana)

Published on: March 17, 2017

Acoustical coupling of lizard eardrums.

Jakob Christensen-Dalsgaard1, Geoffrey A Manley

  • 1Institute of Biology, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark. JCD@biology.sdu.dk

Journal of the Association for Research in Otolaryngology : JARO
|July 24, 2008
PubMed
Summary
This summary is machine-generated.

Lizard ears achieve remarkable sound directionality through acoustic coupling between eardrums. This pressure-difference receiver mechanism, crucial for hearing, is explained by interaural sound interaction.

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Postsynaptic Recordings at Afferent Dendrites Contacting Cochlear Inner Hair Cells: Monitoring Multivesicular Release at a Ribbon Synapse
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A Lightweight, Headphones-based System for Manipulating Auditory Feedback in Songbirds
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Last Updated: Jul 3, 2026

Physiological Preparation of Hair Cells from the Sacculus of the American Bullfrog (Rana catesbeiana)
12:07

Physiological Preparation of Hair Cells from the Sacculus of the American Bullfrog (Rana catesbeiana)

Published on: March 17, 2017

Postsynaptic Recordings at Afferent Dendrites Contacting Cochlear Inner Hair Cells: Monitoring Multivesicular Release at a Ribbon Synapse
11:45

Postsynaptic Recordings at Afferent Dendrites Contacting Cochlear Inner Hair Cells: Monitoring Multivesicular Release at a Ribbon Synapse

Published on: February 10, 2011

A Lightweight, Headphones-based System for Manipulating Auditory Feedback in Songbirds
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A Lightweight, Headphones-based System for Manipulating Auditory Feedback in Songbirds

Published on: November 26, 2012

Area of Science:

  • Bioacoustics
  • Comparative Anatomy
  • Auditory Neuroscience

Background:

  • Lizard ears function as sophisticated two-input pressure-difference receivers.
  • Their unique structure provides significant directionality, outperforming similarly sized terrestrial vertebrates.
  • This directionality arises from acoustical coupling between the eardrums and sound wave interactions.

Purpose of the Study:

  • To quantify the gain of direct and indirect sound components in three lizard species.
  • To investigate the role of interaural acoustic coupling in auditory directionality.
  • To explore the underlying acoustic principles governing lizard ear function.

Main Methods:

  • Laser vibrometry was employed to measure eardrum vibration amplitudes.
  • Stimulation involved free-field sound and headphone/coupler methods.
  • Experiments included occlusion of the contralateral ear to assess its impact on directionality.

Main Results:

  • Pronounced ear directivity was observed in the 2–5 kHz frequency range for Anolis sagrei, Basiliscus vittatus, and Hemidactylus frenatus.
  • Directionality was ovoidal, asymmetrical across the midline, but symmetrical across the interaural axis (front-back).
  • Occluding the contralateral ear eliminated directionality, confirming the importance of interaural interaction. Interaural transmission gain approached or exceeded unity, suggesting acoustic transparency and resonance within the lizard's head.

Conclusions:

  • Lizard ear directionality is fundamentally driven by acoustic interactions between the two eardrums.
  • A simple acoustical model based on an electrical analog circuit effectively explains the observed phenomena.
  • The findings highlight the evolutionary significance of pressure-difference hearing mechanisms in vertebrates.