3D Physiology of Utricle and Saccule - Vestibular System - 3D Ear Embryology Part 3

the Cilia bends like this deflected the  potassium channels open as they move   so here you can see the cup also you see  that there in the last lecture we had seen   the histogenesis of macula of utricle and saccule  and we had seen that there are these supporting   cells and within these supporting cells the hair  cells are embedded and these hair cells they are   harboring the Cilia and Cilia they are gradually  increasing in their size like this and the Cilia   they are embedded within the gel Matrix and  the shell Matrix is called otolithic membrane   and on top of otolithic membrane we have these  Otoconia now one by one we will understand the   basic physiology of utricle and saccule first  if we talk about utricle and saccule so imagine   that there is a guy sitting in the car and car is  moving now what will happen let me explain you if   I zoom inside his head let's suppose we have  made his head translucent and inside the head   we have removed everything else and we are only  looking at macula which is unusually enlarged of   course macula is not this much bigger we have  unusually enlarged to understand that what is   going on inside it so of course we have the  otoconia otolithic membrane and we have these   supporting cells within the supporting cells  are these embedded hair cells now again the   car will start moving and we will see what will  happen with this so let's replay the animation   so here you can see car is moving so what actually  happens that as the race pedal is pushed the   car will accelerate forwards there is forward  linear acceleration and due to inertia this part   of otoconia and otolithic membrane it fails to  catch up with the acceleration so it is displaced   backwards and as the as the uniform velocity is  achieved and as the car is moving uniformly it   will again move forward so here you can see it  is going backward display and now the uniform   velocity is achieved and now it is now undisplaced  so as there is the displacement of this uh let me   show you so as there is displacement of this  uh gel like material otolithic membrane and   otoconia what will happen here the hair cells  will bend so here the hair cells are straight   and here also straight at here now they are  starting to bend like this here you can see   so now if I show you so they will bend and  they will bend a lot so the hair cells at the   posterior at the dorsal side at the posterior  side they are bent a lot they are deflected a   lot but at the anterior end these hair cells  are they are not much deflected so in this   way which hair cells are deflected which are not  as according to this the brain it can sense the   presence of linear acceleration of course it's  a forward linear acceleration so these cells   are deflected their hair cells are deflected so  brain can easily detect of course there are the   nervous connection going on below that there is  the nervous connection neuronal connection and   it will form the vestibular part of vestibular  cochlear nerve so this is how it works now how   the bending of these hair cells how it leads  to depolarization of neurons below it that we   will discuss later but the basic idea is that  this bending can be sensed by our brain and it   helps in detection of forward linear acceleration  forward or backward forward or backward of course   if car starts to move backward the situation will  be actually reversed it will be deflected like   this rather than this it will be deflected like  this so forward or backward linear acceleration   is sensed by which system which organ it is  sensed by utricle not saccule because utricle   is placed horizontally so it is able to detect  the linear acceleration and how exactly that I   have explained to you just to make you understand  that there is the presence of inertia and due to   the presence of inertia it goes backward let me  show you another thing let's suppose that a cup   full of orange juice is also placed in the car  and you can see that as the linear acceleration   starts the cup also is displaced like this and  as the uniform velocity is achieved it goes back   to the to its normal position so this orange  juice is also displaced and this is just like   the displacement of Otoconia and the gel like  Matrix the otolithic membrane I I hope you can   also see that as well in this small part here you  can see that as the cup is being displaced it is   this is also being displaced so that is due to the  presence of inertia here you can see bilaterally   we have these organs I hope you can understand  this now let's suppose that there is this person   standing in an elevator in let's suppose in the  shopping mall and this elevator is connected   with an s-shaped hook to a rope and this rope will  then pull the elevator upwards and that how this   elevator is working so we will see that there  is the role of saccule in sensing this vertical   acceleration the acceleration the axial the linear  acceleration along the vertical axis is sensed by   the saccule so here because this is s-shaped hook  so this is just to make you remember that the   vertical axis the vertical axis acceleration is  determined by saccule S for saccule so this will   help you remember it now what will happen  there this lift will go upward like this   now to understand this phenomena clearly that  what is the role of saccule what I will do is   that I will take a close-up shot of this we will  see a close-up view and in the closer view we will   be able to see what is going on in the macula of  saccule of this person so here is the close-up   view and now if you will see that as the lift  goes upward due to the inertia these deflected   otolith membrane and otoconia and the deflected  Otoconia they will be reversed upward they will   go upward and this will be sensed by the brain  and as uniform velocity is achieved the default   position is also achieved of this Otoconia and  you will see that how it happens let's watch   the animation so here the lift is going upward  and it has achieved this position and then as   the lift has reached to the top floor again it  has gone back to its downward deflected position   so this change in deflection can be sensed by  our brain and in this way the brain sense that   whether there is acceleration along certain axis  actually the whole this process is not very simple   the position of these macular and the hair cell  deflection it varies even along the same even   along the same macula at different parts different  hair cells they are deflected and oriented along   the different axis but we will not go into that  nitty-gritty details I will try to discuss those   when we will discuss the physiology in detail when  we will talk about physiology of vestibular system   but right now you we will follow this simplified  approach in understanding the basic physiology of   macula of utricle and saccule so I hope you are  very clear about this let's watch the animation   again so here the left is going upward and  change in deflection is there and that's it so   we had seen that there was that s-shaped hook that  hooked the rope with the with the elevator so s is   s means secular stands for saccule and saccule is  involved in the vertical axis acceleration linear   acceleration along the vertical axis regarding  the utricle you just imagine that this u-shaped   road is there and this car is moving along this  u-shaped road so this will help you visualize   and this will help you remember that the U for  utricle and utricle is involved in horizontal   axis acceleration and saccule is involved in  which axis acceleration vertical axis so that   is just a bit of mnemonic to make you memorize  these important Concepts also please note that   macula is also involved in sensing the position  of the head for example this is the macula of the   utricle and as the head is tilted forwards like  this so due to the effect of gravity on these   Otoliths the otoliths as well as the otolithic  membrane it will be deflected forwards like this   and here you can see these hair cells the their  cilia will also be deflected I hope you can see   if I hide this for you so here you can see  that their cilia are deflected quite a lot   so that's how it works so this is just the basic  overview of physiology of vestibular system of   course as I have told you it is much more complex  than this but let's not go into that finally I   would also like to talk about that how the bending  of Cilia how it leads to the depolarization of the   cell again I will not go into details but for  the basic idea let's go to another 3D model so   here is the Single Cell basically what happens  that they have the special channels above their   Cilia so here is the channel basically these  are the potassium channels so as the hair cells   are deflected the potassium channels open for  example here if these are deflected like this   these channels will open due to a conformational  change in their structure and they become closed   as they move towards the other direction so  these potassium channels potassium will go inside   them and potassium will go into these cells  which leads to depolarization let me explain   it to you with another 3D animation so here is a  schematic representation of a hypothetical model   of Cilia of the hair cells of the ear so here you  can see this is the largest Cilia and this is the   smaller one let's suppose we have only shown the  two cilias here and we have enlarged them quite a   bit so here are the potassium channels now Focus  here that here this is a potassium Channel and   it has been closed by a certain protein please  don't assume that these are the corks of the wood   well this is just a schematic depiction actually  these are the proteins which actually block these   channels but these are not wood corks right  and these spring-like things these are also   proteins now what will happen that as the Cilia  bends like this the spring will recoil back and   it will lead to opening of these opening of  this channel so here you can see the channel   has been opened because the spring sort of  pull back these are not Springs these are   actually proteins so due to deflection there  is the conformational change in these proteins   Which pull back the other proteins these Channel  blocking proteins I will not go into the names   of these proteins but you need to understand the  basic mechanism that how it is working so this is   important for you to understand the mechanism  just by looking at this animation you can use   easily understand this now as this channel  potassium Channel opens lots of potassium   will rush into the cell now the question arises  why potassium rush into the cell the answer is   that number one there is too much potassium in  the endolymph but then you will ask Dr Aizaz   cell also has too much potassium inside it you  know intracellular fluid has a lots of potassium   as Dr Najeeb says the cells are bags of potassium  surrounded by sodium so any cell including these   vestibular hair cells they contain a high amount  of potassium so endolymph the fluid around this   let me explain it for you the fluid around it is  also rich in potassium so the fluid around it is   also rich in potassium this fluid around it it  is also rich in potassium but the cell they are   also rich in potassium so why the potassium it  quickly rushes along the concentration gradient   into the cell the reason is that the potassium it  is not just about potassium inside the cell there   is lot of negative charge there is lot of negative  chai there is negative resting membrane potential   just like any other cell most of the cells have  negative resting membrane potential and there are   certain reasons for that we will not go into the  reasons but one thing I will just tell you but   before that let me explain you that the potassium  it does not just move along the concentration   gradient where what we say what they say in  textbooks is that the potassium from the Endolymph   moves into the hair cell along the electrochemical  gradient it is not just chemical gradient it is   electrochemical gradient because if it was just  the chemical gradient there isn't much difference   between the potassium inside the endolymph and  potassium inside the cell it is almost the same   yes there is some difference but it is nearly  the same it is also the electro part which is   the driving Force let's not go into detail but  last thing that I want to mention about this is   that so what is actually happening here is that  as I have told you that these hair cells these   are embedded into which cells these are embedded  inside the so let's suppose this is a hair cell   and this hair cell is embedded inside which cell  it is embedded and surrounded by supporting cells   it is nicely embedded and surrounded by supporting  cells so supporting cells they provide structural   Support and not just structural support but they  also provide functional support to it functional   support in what sense that the potassium that  comes inside it through these channels this   potassium will be picked up by these supporting  cells and these supporting cells will then recycle   this potassium back into endolymph so in this way  the negative charge the negative the negativity   then not negativity I mean negative current inside  it resting membrane potential that is maintained   inside the cell I don't think so they are negative  they are negative in emotional sense they are   quite positive cells they are happy that they are  performing this function of sensing the motion   and sensing the position of head and sensing the  linear acceleration so these are actually positive   emotionally but they are negatively charred  please keep that in mind so that's how this   process is going on of course there are certain  other factors that are involved in maintenance   of resting membrane potential of these cells but  we will not go into that in this lecture I hope   you learned something from this video thank you  so much for watching this video have a nice day

Channel: MedicoVisual - Visual Medical Lectures

Views: 1,719

Keywords: vestibular system, physiology, utricle and saccule, utricle, saccule, physiology of vestibular system, physiology of utricle and saccule, physiology of ear, how vestibular system works, medicine, dr najeeb, biology, human, balance, inner ear, vestibular, the vestibular system, anatomy, histology, macula, cilia, hair cells, science, ear, biophysics, vestibule of inner ear, membranous labyrinth

Id: MGLXc6qGULg

Length: 17min 4sec (1024 seconds)

Published: Sat Jul 08 2023