[MUSIC] Okay. So let's go over the hearing pathways in in, an overview of the hearing pathways. Before we get to that, I'd like to just introduce you to sound waves. Sound waves are waves of pressure, of mol, molecular pressure, and there are two key components of the sound waves that we're going to think about. One is frequency, the, how many cycles per second, which is called Hertz. And I, you can see that speech extends from about 250 hertz to maybe around 3,000, 3,500, close to 4,000 hertz. So you might also hear the word kilohertz, so 4,000 is 4 kilohertz. A kilhertz is 1,000 hertz. And this just gives you the range of different if you're listening to an orchestra, the contrabassoon is very close to zero, it's about six or so hertz. Whereas the piccolo, might be closer to eight or ten kilohertz. And, and different consonants and different sounds in speech are lower or higher in frequency. And that will become important in a bit. Okay so the second aspect of sound that, that we need to understand is the is the intensity which we interpret as loudness. And so zero decibels is actually the detection threshold for a the, the most, the smallest amount of sound that we can detect. So, a ticking watch is, I don't know, around 20, decibels. A whisper is around 30. A conversation, just normal conversation, is around 60 decibels. Shouting is up around 80 or 90 decibels. A vacuum cleaner is 70. A leaf-blower, one of the true evils in this world in my opinion is around 100 decibels. An ambulance sirens siren is around 130, so the we are exposed in modern life to a lot of decibels a lot of the time as I walk from the train to my laboratory. I pass busy traffic, I pass leaf blowers, I hear am, ambulance sirens. There is just a lot of ambient noise in the modern world, and that is, that will also become important later. Okay, so the sound is coming in from the outside. And it's coming in through the air and the whole point of the ear, from the external ear to the inner ear, is to transform an airwave into a fluid wave. Because the external ear only carries air, and the inner ear is fluid-filled. So, we are going to transform the sound wave, the pressure wave from air to fluid. So the external air, ear is air, the middle ear is actually essentially a drumstick. We're going to take that ear and push, and make it push on a drumstick, so we're going to go boo boo boo, onto this fluid filled cochlea. From there, the a nerve takes the information, a cranial nerve takes the information into the brain. And that's shown here, the cranial nerve is right here. It has a vestibular and a cochlear part. Today, we're only talking about the cochlear part. And from this point on, what happens is that, very rapidly, information from each ear gets sent to both sides. So, it's bilateral. As a result there is virtually nothing that you can do to impair hearing with a central lesion, until you get up into cortex. Consequently, all hearing loss is either the nerve or, most commonly, out in the ear, okay? And so what we're going to do is we're going to follow from, the external ear. We're going to talk about the middle ear, we're going to talk about the inner ear, and we're going to spend quite a bit of time on the inner ear. And then we'll we'll put it all together and understand and understand how, how we do hear and how we also lose hearing. All right. So in the next segment we'll talk about the external ear. [MUSIC PLAYS]
