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Auditory structure - part 2

The cochlea, a snail-like structure in the ear, transforms soundwaves into neural impulses. The stapes bone vibrates, pushing fluid through the cochlea, which moves the organ of Corti. This motion triggers hair cells, causing potassium and calcium to flow into the cell, firing an action potential. This signal then travels to the brain via the auditory nerve. Created by Ronald Sahyouni.

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  • male robot hal style avatar for user Okilus
    Wouldn't potassium move OUT of the hair cell instead of into the cell?
    (17 votes)
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  • female robot ada style avatar for user mariamikaleem
    Hello I needed a little clarification at : Should the filaments/ cilia of the hair bundles be referred to as kinocilium or stereocilium?
    Is it a mistake on my part to think the fillaments that Ron mentioned should be called Stereocillium, since Kinocilium are actually lost in humans shortly after birth (source:http://www.ncbi.nlm.nih.gov/books/NBK10867/) and there are only stereocilia in the auditory system and no kinocilium -which are only found in the vestibular system only ( source: http://www.d.umn.edu/~jfitzake/Lectures/DMED/InnerEar/TestQAnswers/Answer7.html)

    Therefore the correct term to be used is stereocilium/ stereocilia and not Kinocilia?

    Please correct me if I am wrong? thanks
    (24 votes)
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  • marcimus pink style avatar for user Ci Qian W
    just that stretching and potassium and calcium can enable us to experience all kinds of different sound? it's amazing!
    (19 votes)
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  • blobby green style avatar for user Michela Rocha
    What is the fluid in the cochlear called?
    (6 votes)
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    • aqualine ultimate style avatar for user youngmbrandon
      Actually there are 3 chambers in the Cochlea. They are known as Scalae. Two of the three scalae, the scala tympani and scala vestibuli, contain perilymph. The scala media, also known as the cochlear duct, contains endolymph. The fluid motion is actually perilymph moving in the scala vestibuli and then rounds over and back to the round window as in the last video. The perilymph on the outer two channels then causes the endolymph of the scala media to vibrate, then the hair cells, etc.
      (22 votes)
  • piceratops ultimate style avatar for user Curiosititis
    Around : This is a little bit confusing. Is the fluid medium moving in bulk around the cochlea or is it the pressure waves traveling from the elliptical window to the circular window? If it is the fluid moving from the elliptical window and around the cochlea, what happens to the fluid when it reaches the circular window?
    (3 votes)
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    • leafers ultimate style avatar for user Arnoldeen
      The fluid medium "moving" refers to the pressure waves passing through it. Think of ripples in a swimming pool. The water molecules are moved, but remain contained. When the ripples, or pressure waves hit something solid, some of the energy is lost, but the ripples can 'bounce' back or reverberate.
      The receptor hairs are so specialized that they only send a positive impulse if they are bent a specific way, so the pressure waves traveling back won't trigger the same receptor 'hairs'.
      (11 votes)
  • male robot donald style avatar for user Jian Liang
    I think what shown at - might not be accurate, as shown (http://media-2.web.britannica.com/eb-media/01/14301-004-4B6F34DA.jpg or Principle of neuroscience 5th Ed. P657). The fluid will not flow from scala vestibuli alongside of tectorial membrane to scala tympani . They are isolated. The flowing direction should be perpendicular to the direction drawn in the video. What caused the the tectorial membrane move to push the hair cell is the physical phenomena of Resonance (Principle of neuroscience 5th Ed. P659 Figure explaination item E) instead of fluid flow push. what the flow push should be whole scala media. Please correct me if I misunderstood anything.
    (6 votes)
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  • male robot hal style avatar for user bpoole9925
    So is there any correlation to the sodium channels like there are in neural cells? IE... sodium channels open and influx sodium while potassium channels open and eflux potassium to cause an action potential... just wondering because it seems logical to think that if one type of cells generate an action potential then the others would follow a similar path.
    (3 votes)
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    • leafers sapling style avatar for user Noscere
      The K+ channels in hair cells do similar functions as the Na+ channels on neurons, but hair cells alone cannot generate an action potential.

      Hair cells aren't neurons, so they don't produce action potentials. They are found within the cochlear duct, which has a fluid called "endolymph" filling it. Endolymph is special because it is high in K+ unlike most extracellular fluids. When the stereocilia move in a way to open up the mechanogated K+ channels, K+ enters the cell. The resulting depolarization also opens Ca2+ channels, which are needed for neurotransmitter (NT) release. The NT travel across the synapse to the receptors on an afferent neuron, which will conduct the action potential to the brain.
      (5 votes)
  • blobby green style avatar for user tiarnan.odoinn2
    Is the top and bottom membrane of the organ of corti synonymous with the basilar and tectorial membrane, respectively?
    (1 vote)
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  • leafers ultimate style avatar for user Daniel
    At he talked about how the fluid moving over the organ of corti triggers hair cells. Why then, if we swing our head, do we not hear random sounds as the fluid in the cochlea triggers random hair cells?
    (3 votes)
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  • blobby green style avatar for user deliamariacoman16
    So the cell sends action potantial when it is in its hyperpolarized state?
    (2 votes)
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    • marcimus pink style avatar for user Valentina
      No, the potassium is entering the cell instead of leaving it. This is because the hair cell is in a special type of fluid called endolymph that has an unusually high concentration of potassium, so its driving force is reversed and moves INwards. Also, hair cells do not fire action potentials; they're so short that they don't need to. They actually aren't even neurons, the first neuron in the auditory pathway is the spiral ganglion cell.
      (2 votes)

Video transcript

Voiceover: Okay, so now let's take a closer look at the cochlea and the inner ear. Let me just draw a little cochlea. So, it's this round, snail-like structure, but let's go ahead and unroll it, so we'll just unroll it and lie it flat. So, if we unroll it, it'll look something like this. It looks something like that. So, basically this is just a flattened cochlea, and so you've got this little bone that we were talking about earlier which is called the stapes. So, you've got this little bone right here, it's called the stapes, and this stapes is connected to the other two bones and then the eardrum, so it's basically moving back and forth at the same frequency as the soundwave that's making the eardrum move back and forth, and this stapes is connected to this little oval membrane called the elliptical window, and the elliptical window gets pushed in and out as the stapes moves back and forth. So, as the elliptical window gets pushed in, there's fluid inside the cochlea. So we've got fluid inside and that fluid basically gets pushed all the way around the cochlea and then comes back around, and as I mentioned before the reason that the fluid flows in this direction is because there is actually a structure right in the middle, there's this little structure, and we call it the organ of Corti. So, this organ of Corti kind of splits the cochlea in two, and the fluid can only flow in this direction. So, when the fluid gets over here, there's this little round window, it's actually called the circular window, and the circular window gets pushed out a little bit as the fluid kind of compresses it. So, now you've got fluid flow back and forth around this organ of Corti. So, what we want to look at now is we just want to look at a cross-section, just a little cross-section of this organ of Corti so that we can kind of understand what happens, how does it turn this fluid motion into sound. So, if you actually kind of look at a cross-section, what you would see is something like this. It's something like this. So, you've got an upper membrane and a lower membrane, and you've also got these little hair cells. So, you've got little hair cells with little shark fin looking things on the tops. So, you've got these little hair cells, and basically as there's fluid flow around this organ of Corti, it goes like that and then the fluid kind of comes around and goes this way, so as we have fluid flow it actually pushes down on this membrane and pushes up on this membrane, so you can kind of imagine how this fluid flow works. So, as this membrane gets pushed up and down, it actually causes these little hair cells to move back and forth. So, they're moving back and forth, they're vibrating, and basically what we can do is we can blow up these hair cells so we can blow them up and look at them in a little bit more detail, so it kinds of looks something like this. So, there's their shark fin part and then there's the cell. So, the shark fin part actually is called the hair bundle. Hair bundle. And these aren't actually hairs. What they are is they're just a bunch of little filaments. And let me just draw, a little bit bigger, so if we were to look at just the hair bundle, it would look something like this. It would look something like this, and each one of these filaments is called kinocilium. Kinocilium. So, basically a whole bunch of these little filaments are attached to one another and they form the hair bundle. So, each kinocilium is actually connected to one another by this little spring-like structure called a tip link. So, it's a little spring-like structure and each one is called a tip link, so it links the tips of the kinocilium. So, if we were to actually look at a tip link, so let's go ahead and look at just the tip of this kinocilium, if we were to look at just the tip of this kinocilium, it would look something like that and you've got the little tip link attached to it, so you've got this little spring-like structure attached to the tip of this kinocilium, and in fact the tip link isn't attached to the kinocilium directly but it's actually attached to the gate of a potassium channel. So, there's the little gate right here, so this is the little gate of a potassium channel. And so as these hair cells, as the little kinocilia get pushed back and forth because the fluid is moving in the cochlea, as they get pushed back and forth, it actually stretches on this spring. So, let's say that the kinocilium gets stretched. Sorry, we're going to use this color over here. Let's say that the kinocilium gets stretched. It actually kind of looks like this, so now it's getting stretched, and as it gets stretched it actually opens up this gate. So, as the potassium channel gate opens up, there's potassium outside that then flows into the cell. So, you've basically got potassium out here flowing into the cell, and there are actually all these other little channels, calcium channels, that get activated when potassium is inside the cell, so now you also have calcium flowing into the cell, so the flowing of potassium and calcium into the cell basically causes the cell to fire an action potential, so it basically stimulates another cell, which is known as a spiral ganglion cell, and the spiral ganglion cell then activates another cell that is part of the auditory nerve which then goes to the brain. So, basically this goes to the brain. So, this is what happens when a soundwave comes into the ear and then gets transmitted into a neural impulse by these little hair cells.