 Hello friends how are you doing today? Today we are going to talk about a very difficult topic but a very important one also that is the organ of cortisol. So let's straight deep dive into the topic. So here is a diagram which is showing the cochlea. Now cochlea is like a labyrinth you see that it is taking some turns right so these are like two and a half turns cochlea takes and actually outside there is bony labyrinth. Labyrinth is anything which is very difficult to navigate okay. So this is the bony labyrinth and inside this bony labyrinth there is membranous labyrinth. So this outer walls which you are seeing form the bony labyrinth and inside we have membranes which divide this space inside the bony labyrinth into scala vestibulae and scala timpani. So there are two membranes actually. So here what we see is a top membrane. This membrane is known as reasonous membrane and then there is a bottom membrane. Bottom membrane is the basilar membrane and it is these two membranes which divide the cochlea into three parts where the top part where the first layer will be this is the bony labyrinth and the bottom will be the reasonous membrane. Top part is known as scala vestibulae. How I remember up? Up is vestibulae okay uv, uv come together in letters right so up is scala vestibulae. The below part which is again up bound by basilar membrane and below there is a layer of the bony labyrinth that is a scala timpani and in between these two compartments there is another compartment that is the scala media. Now on this scala media is present organ of cortex. So that is the sense organ the hair cells which are there for hearing they are present in this organ of cortex. Now how this organ of cortex is arranged in this cochlea? You see that this cochlea if it is running like this throughout the length of the cochlea in a transverse manner like this there is organ of cortex in the scala media. So here everywhere transversely there will be organ of cortex. So please remember that throughout the length of the cochlea there is organ of cortex so sense organs are present throughout the length. So this is a cut section of the cochlea where you see the various membranes and the organ of cortex and again as I was telling how it is arranged. So this cochlea will continue like this and there is a cut section where it is showing the various compartments okay. So top one is a scala vestibuli, bottom one is a scala timpani and in between there is a scala media and on the scala media in the scala media I mean you see these are this component is the organ of cortex. So we will be studying this structure in detail. So see how it is arranged it is in transverse manner. So it will extend like this throughout the length of the cochlea. So I just wanted to show you the arrangement of this organ of cortex that's why I had put this diagram. So let's straight move into the organ of cortex structure. So this is the basic structure of the organ of cortex. Now what is this blue line showing? What will be the membrane? We have seen that it is present on the scala media and the scala media is bound on top by the reasonous membrane and in bottom by the basilar membrane. So this blue line is showing the basilar membrane over which the organ of cortex is present with hair cells. On the top if you see I have not drawn reasonous membrane rather there is another membrane, tectorial membrane. So let us go back to the previous diagram. So this was the diagram which we saw. You see this is the reasonous membrane here. This part is the reasonous membrane and organ of cortex top portion it is not touching the reasonous membrane. Here what I am talking is that there is another membrane and this membrane is the tectorial membrane. Fine. So let us go back to our detailed diagram of organ of cortex. So what we see here? Bottom there is basilar membrane and top there is tectorial membrane. So let us see what are the various other components. So there are various kind of cells present in this organ of cortex. So let us just enumerate the types of cells here. There are pillar cells also known as the rods of cortex. Then there is hair cells and in this hair cells we have two different types. There are inner hair cells and there are outer hair cells. Then there are supporting cells. So all these green ones which you see these are supporting cells and they have different names. Deter cells, Hansen cells, three four types of supporting cells are there. Then the main part that there are hair cells which are protruding. The part of the hair cells is protruding into the tectorial membrane. So what are the types of cells? There are pillar cells one. There are hair cells which we have inner hair cells and there are outer hair cells and then there are supporting cells. So these are the various types of cells. Then the membrane is basilar membrane. There is tectorial membrane. There is another membrane which is known as reticular lamina. Okay. So what is the arrangement of these cells and membrane within the organ of cortex? You see all the supporting cells are extending from the basilar membrane up till the reticular lamina. So this is the reticular lamina and they are kind of supporting the hair cells. We have basically one row of inner hair cells. So this is just one cell showing here. We cannot show you the row but as I told you it extends throughout the length of the cochlea in a transverse manner. If a cochlea is extending longitudinally then this row will be extending transversely throughout. So that is one row of inner hair cells and here we have three rows of outer hair cells. So two types are there. One row of inner hair cells and three rows of outer hair cells. These hair cells are supported by supporting cells and these hair cells have processes and these processes are known as stereocilia which you see have certain characteristics. First of all there is this reticular lamina and the stereocilia is piercing this reticular lamina. It is kind of piercing this reticular lamina and the top of the stereocilia is embedded in this tectorial membrane. So this is very important for the transduction process that is conversion of any auditory signal which will be coming as pressure waves in the cochlea. These pressure waves are transduced to electrical signal by these hair cells. So hair cells are the transducing cells or the receptors of hearing. So that is the structural aspect of hair cells. Also you see that there is a tunnel of coty. This is the tunnel of coty which is basically bound by the pillar cells that is the rows of coty on either side. So on the medial side of the tunnel there is hair inner hair cell and on the lateral side of the tunnel there is outer hair cells and these hair cells they are innervated by neurons okay. So there are neurons which are innervating both these inner hair cells and outer hair cells and immediately they go into the part of the bony part of the cochlea that is the modulus modulus and there is presence of spiral ganglion hair. That is the cell bodies of the neurons are there. Ganglion whenever we say there are cell bodies of neurons. So inner hair cell present immediately to the tunnel outer hair cells present literally to the tunnel. So that is the basic structure of the organ of coty. Now what is the use of all this structure? See whenever there will be a pressure wave that is here there will be reasoner's membrane. The pressure wave is going to travel and it travels via the end of the cochlea where that is the apex of the cochlea and it travels into the scalar tympanic part of the cochlea. So that is the pressure wave. So it will cause the vibration of this basilar membrane. So it will start vibrating okay. Now with the vibration what will happen the all the structures which are present on the basilar membrane they will also start to vibrate. So when the basilar membrane starts to vibrate up this will cause the vibration of these cells also up and also the hair cells that will also move up along with that they will move to medial side. The stereocilia if you are see they are kind of fixed right in the reticular lamina as well as on the tectorial membrane. So this tectorial membrane is kind of gel like okay. So with the movement of the basilar membrane up and the hair cell up there will also be movement of the stereocilia towards the medial side right. So all the stereocilia will bend towards the medial side and vice versa. So if the basilar movement is down the hair cells will also move down and also outwards that is towards the lateral side. So this movement of stereocilia of hair cells is responsible for transduction. So these inner hair cells are responsible for transduction. Then what is the use of outer hair cells? Well these outer hair cells are responsible for changing the sensitivity of response of inner hair cells means see these outer hair cells are inner weighted from efferents efferents from the central nervous system. The neuron from the inner hair cell is the afferent. It is carrying the information to the central nervous system but from the central nervous system the information is coming to the outer hair cells. So whenever there is a depolarization of the outer hair cells these hair cells actually shorten in length. Actually there is a motor protein within these hair cells known as pristine okay. So when that is activated these hair cells shorten in length and when depolarization is not there at the resting state these will lend then or there can be hyperpolarization also and these can lend then. So when they shorten it is kind of making the structure stiff okay. So information from central nervous system is making the movement of the organ of cortex stiffer and hence there will be less movement of these stereocilia of the inner hair cells and contrary will happen when there will be less signals to these outer hair cells that will cause them to lend then thus changing the sensitivity of response of the inner hair cells. So I hope in this short video of organ of cortex I have tried to deliver the concept a difficult concept of the structure of organ of cortex how the cells are arranged and how outer hair cells are changing the sensitivity what is the importance of outer hair cells. Now remember one more thing here that this basilar membrane which we talked about its structure also changes throughout the length of the cochlea actually at the apex of the cochlea the structure is such that the membrane vibrates more in response to low frequency sounds okay and at the base of the cochlea that is where the cochlea is starting where the steps is attaching to the cochlea there this basilar membrane vibrates more to high frequency sound so there actually this basilar membrane is quite stiff and due to its stiffness it will vibrate only to high frequency sounds. So the structure is similar rest of the structure is similar hair cells are similar only the vibrating pattern is changing from the base to the apex of the cochlea and that is why there is a spectrum to which the cochlea responds from the base to the apex spectrum moves from high frequency to lower and lower frequency sounds. This coding of information for sound I have dealt in another video on theories of hearing I will give the link in the description section below you can check out that video as well thanks for watching the video if you liked it do press the like button share the video with others and do not forget to subscribe to the channel physiology open thank you