hey there welcome back to my channel uh in this video I'm going to discuss the vestibular apparatus and its role and its importance as to what it is doing I have actually divided this topic into two videos in the part one that is in this video I will be concentrating on the structure of the vestibular apparatus because understanding the structure is extremely important in order to understand its function whereas in the part two of the video which I will be uploading little later I'll be concentrating on the vestibular pathway as well as the role or the mechanism of stimulation of the semicircular canals so let's start this video so what is this vestibular apparatus vestibular apparatus is nothing but it's a sensory organ okay it's a sensory organ so what it is going to detect it is going to detect the sensation of motion so once it detects the sensation of the motion it is very much helpful for the body in order to maintain what is called as equilibrium as well as the posture so both these things it's very important in maintenance of equilibrium and posture so in order to understand how this vestibular apparatus functions we have to know the location and the structure of the vestibular apparatus so in this particular slide we are looking at the structure of the ear this is the Pina this is this is the external auditory canal and these both they constitute what is called as the external ear this is what is the tanic membrane so the tanic membrane is acting like a border between the external ear and the middle ear and this is the middle ear which contains the ear OES now what we are interested in is this part of the ear and this is what is called as the inner ear this is what is called as the inner ear because this inner ear is the one in which our vestibular apparatus is present now as we are looking at the inner ear we can see that the inner ear is made out of lot of bony tubules okay this bony tubules is what is called as the Bony Labyrinth now this is how that bony Labyrinth is going to look on one side the Bony Labyrinth is having this uh part which is called as the ccka and on another side it is having these canals which are called as the semicircular canals and connecting the ca with the semicircular Canal is this part which is called as the vestibule so this ccka is the one which is concerned exclusively with hearing and it is not going to take any part in the vestibular apparatus now when we go inside this bony Labyrinth we also find that inside the Bony Labyrinth there is a system of membranous tubules and this system of membranous tubules is what is called as the membranous Labyrinth so this outer part which we are seeing is what is called as a bony Labyrinth and this inner part what we are seeing that is what is called as the membranous Labyrinth and a fluid is present in between the membranous Labyrinth and the Bony Labyrinth that fluid is what is called as the Peril lymph that is called as the Peril lymph even our membranous Labyrinth on the inside of the membranous labyrinth in this area all this area there is a fluid and that fluid is what is called as the endolymph okay this is very important that is what is called as the endolymph so this endolymph if we look at the contents of the endolymph the contents of the endolymph are similar to the contents of the intracellular fluid that means the endolymph is rich in potassium so this point is very important in order for us to understand how the vestibular apparatus is going to function now as I I have already told you this part is what is called as the ccka and this part is not taking part in the vestibular apparatus and this is a part which is concerned only with the hearing so what are the parts which are take which which form the vestibular apparatus they are these semicircular canals the anterior semicircular Canal the lateral semicircular canal and the posterior semicircular Canal then I told you while discussing the Bony Labyrinth that there is a there is a connection between the ccka and the semicircular canal and that part is what is called as a vestibule so when we go inside this vestibule and see we see that there are two structures one is what is called as a utricle and another one is called as a sacul so that means our vestibular apparatus is formed by these structures the three semicircular canals the utricle and the SACU now when we look at the semicircular canals we see that one end of the semicircular Canal is showing this expanded portion here you can see this expanded portion these expanded portions of the semicircular canals is what is called as the ampulle and these ampul they contain the sensory organ which is present in the semicircular canal and that is what is called as Christa ulis that is called as a Christa ulis now this Christa illis is going to sense or it is going to detect what is called as angular acceleration okay angular acceleration or few books also mention that as rotational movement or rotational acceleration now coming to this utricle and SACU the utricle and SACU taken together they are called as what is called as the oolith organs they are called as the oolith organs and the utricle and SACU are also having a sensory area which is present inside them that is what is called as the macula that is called as macula and this macula is going to sense what is called as the linear acceleration that is going to sense the linear acceleration fine this is with this is the this is how the structure of the vestibular apparatus is so the vestibular apparatus consists of three semicircular canals expanded end of the semic cular Canal is called as the ampula and the ampula consists of Christa ulis and the Christa ulis is detecting what is called as angular acceleration or it is also called as rotatory acceleration or the rotatory movement so once it detects this angular acceleration it is helping the body to maintain what is called as dynamic equilibrium okay dynamic equilibrium now in the utricle and maula in the utricle and the SACU we have what is called as the maula and this macula is the one which is sensing what is called as the linear acceleration and the linear acceleration once it senses the macula is helping in maintaining what is called as static equilibrium static equilibrium okay so the dynamic equilibrium is nothing but maintenance of the position of the head Whenever there is an angular acceleration the static equilibrium is nothing but again maintenance of the position of the head Whenever there is a linear movement or a linear acceleration now both the Christa ulis and the maula they have the receptor cells and these receptor cells are what is called as the hair cells so in the next slide we are going to understand the structure of the hair cells usually there are two types of hair cells the type one and type two let's not go into the details of the types of the hair cells let's just understand this diagram so here we can see the hair cell is a flask shaped cell and from the top end of the hair cells we are seeing about 50 to 70 short Celia are arising these are called as the stereo Celia but from one end of the hair cell there is a long celium and that is what is called as the kyos helium now one thing that we are noticing in this diagram with with respect to the stereocilia is that the height of the stereocilia is progressively decreasing from the kelum end to the other end one more thing about the stereocilia is that the tips of this stereocilia they are connected by what is called as the filamentous attachments okay these filamentous attachments are also called as the tip Lings so actually these tip Lings are the one which are connecting a mechanosensitive channel which is present at the top of the stereo Celia so what is that that is a mechano sensitive Channel mechanosensitive ION channel that is okay so these mechanosensitive ion channels are the one which are connected by this filamentous attachments which are moving from one tip of one tip to the another tip of the stereocilia so now what is happening is that uh this hair cell is present in fluid and that fluid is what is called as the endolymph so whenever there is either a angular acceleration or a linear acceleration there is going to be the movement of this endolymph which is present inside the membranous Labyrinth now because of the movement of the endolymph the stereocilia are also going to move so the stereocilia may move in the direction of the kinos helium or they may move away from the kinos helium so when whenever the stereocilia are moving in the direction of the kyos celium these Tipp Lings are going to open up these mechanosensitive channels and the endolymph is rich in potassium now because of the opening of the mechanosensitive channels because of the movement of the stereo celium towards the kyos celium the potassium is going to enter inside the celium and hence it is going to go inside the cell so once the potassium enters inside the cell the cell under goes depolarization so whenever the cell is undergoing depolarization there is going to be opening of the volage Gated calcium channels and that is going to cause release of the neurotransmitter which is called as the glutamide and exactly opposite is going to happen whenever the stereocilia are moving away from the kinos helium so when the stoia move away from the kinos celium instead of depolarization what is going to happen we are going to get what is called as hyperpolarization fine so whenever there is depolarization and release of the glutamate there there is going to be nerve transmission so here we can see that from the bottom of the hair cell there are nerve fibers which are arising these nerve fibers are nothing but these are the afferent nerve fibers which are going to form what is called as the vestibular division of the eighth cranial nerve so whenever the cell is deol IED because of the movement of the stereo celium towards the kinocilia what is going to happen there is going to be an increase in the activity in the nerve fiber but when the stereocilia move away from the kyos celium the cell is going to under hyperpolarization and the activity in the nerve fiber is going to decrease so this is what we are supposed to understand with respect to the hair cells next let us understand the structure of the Christa ulis which is a recept are present in the semicircular canals so this is the cryistal illis here we can see these are the hair cells and these are the Celia here what we are seeing is that the Celia is embeded in a thick gelatinous substance and that substance is what is called as a cupular terminalis and here we also have the endolymph so what does the Christa ulis detect cryistal ulis is going to detect the angular M so whenever there is an angular m there will be movement of the endolymph and because of the movement of the endolymph there will be displacement of the cupular terminalis now the cupular terminalis can be displaced either this side or that side so depending upon which side the cupular terminalis is displaced the stereocilia can move towards the kinos helium or it can move away from the kinos helium so if it is moving towards the cell is going to undergo depolarization and there is going to be an increase in the activity in the nerve fibers and the reverse is going to happen that is whenever there is hyperpolarization the activity in the nerve fibers is going to reduce now apart from the receptor cells there are also supporting cells and there is also one more group of cells which is called as Plum semun atom these are basically the secretory cells fine this is with respect to the Christa ulies next receptors are The receptors which are present in the oolith organs which are nothing but the utricle and the SACU so in the utricle we are having the hair cells and the hair cells are arranged in a horizontal plane and here we can see there is also Celia and here the Celia are embedded in a membrane which is called as the oolith membrane now the oolith membrane is little bit different from the cupular terminalis because the oolith membrane is having these crystals which are made out of calcium carbonate and these crystals are also called as aonia they are called as the aonia so because of this calcium carbonate crystals which are present in the oolith M the specific gravity of the ool membrane will be higher than that of the Endy okay and here we are seeing one more thing is that in the utricle the hair cells are present in a horizontal plane because of that the utricle is going to detect the linear acceleration but that linear acceleration is detected in horizontal Direction it is detected in the horizontal Direction whereas in the SACU we are seeing the hair cells are present in the vertical plane and Celia is here and this is the oolith membrane that's why the SACU is going to detect the linear acceleration in the vertical Direction the best example that I could give you when there is linear acceleration in the horizontal direction is when the person is moving in the car and the best example I can give you when there is linear acceleration in the vertical direction is that is when the person is moving up and down that is what happens when the person moves up and down in the lift so this is with respect to the structure of the vestibular apparatus I hope this video was very simple for you to understand and it will be very helpful for you to write if this question is asked in the examination if that's the case please please like this video share this video as as much as possible among your friend and do subscribe to my channel and in the second part of this video I will be dealing with the vestibular pathway as well as the mechanism of stimulation of the semicircular canals thanks a lot for watching