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Cochlea

by Craig Canby, PhD
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    The cochlea is the structure of the inner ear that harbors the cellular machinery of the auditory apparatus. Its characteristics are very, very unique in order for it to carry out its marvelous function. The first thing that I want you to know about the cochlea is that it has two labyrinths. One of these is the osseous labyrinth. The bony canal of the cochlea is along in through here. Here is the outer bony wall of the cochlea as it spirals internally within the inner ear. Then here’s the other side of that bony canal that coils within the inner ear. Running within this osseous labyrinth is a membranous component. This is the membranous labyrinth. We see it in blue. It too will follow the coiled nature of the bony labyrinth. Then, it will end here finally at the apex of that coiled cochlea. If we take a cross section through the bony or osseous labyrinth and the membranous labyrinth, this is the profile that we’ll see. In that profile, we will have three scalae. Here is the scala vestibuli. Here’s the outer portion of the osseous labyrinth. On the opposite side, we have the scala tympani. You can appreciate the bony wall of the osseous labyrinth here. Then between the scala vestibuli and the scala tympani, we have the scala media. This is also referred to as the cochlear duct. Now, the cochlear duct has a specialized fluid called the endolymph. The scala vestibuli and the scala tympani have extracellular fluid that’s termed perilymph. The endolymph, however, is very, very unique in its ionic concentration. Normally, extracellular fluid is very, very low in potassium. However, the scala media, its endolymph is extremely high in potassium ion concentration. This assists very greatly in the depolarization of the hair cells...

    About the Lecture

    The lecture Cochlea by Craig Canby, PhD is from the course Auditory System and Vestibular System. It contains the following chapters:

    • Cochlea
    • Organ of Corti

    Included Quiz Questions

    1. Scala media
    2. Osseous labyrinth
    3. Scala vestibule
    4. Scala tympani
    5. Membranous labyrinth
    1. Higher concentration of potassium in the endolymph helps in the depolarization of hair cells.
    2. Endolymph is secreted by hair cells.
    3. It increases the ATP requirements of the hair cells.
    4. It helps in the repolarization of hair cells due to higher sodium concentration.
    5. It has very low concentration of potassium which is helpful in depolarization of hair cells.
    1. Its base is sensitized for high frequency sounds.
    2. Its base is sensitized for low frequency sounds.
    3. Hair cells are embedded in the basilar membrane.
    4. It separates the Scala vestibule from the Scala media.
    5. Its apex is sensitized for medium frequency sounds.
    1. Spiral ganglion
    2. Ptrygopalatine ganglion
    3. Stellate ganglion
    4. Ciliary ganglion
    5. Otic ganglion

    Author of lecture Cochlea

     Craig Canby, PhD

    Craig Canby, PhD


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