learning objective number two is now looking inside the ear and specifically at The receptors for equilibrium which are located in the Vestal and the semicircular canals but before we get to The receptors we need a little bit of background on equilibrium and So within the body equilibrium refers to a state of balance and stability maintained by the vestibular system the vestibular system which can also be referred to as the vestibular apparatus is made up of the vestile and the semicircular canals and they detect changes in head position and body movement The receptors in the vestibular system send signals to the brain to help coordinate movement maintain posture and stabilize gaze any disruption to these receptors can result in vestibular disorders or motion sickness as well as feelings of dizziness vertigo or imbalance so the vesal is this middle portion of the in ear here right between our semicircular canals and our ccka so the VES is made up of our bony Labyrinth within that bony Labyrinth we have the utricle and our sacle so these make up part of our membranous Labyrinth now our utricle and our sacul are small fluid fi Sachs which aligned with sensory hair cells that detect linear acceleration and also changes in the position of your head so the Vesti which as we now know is made up of the utricle and the sacle contain The receptors for what we call static equilibrium static equilibrium refers to maintaining the position of the body relative to the force of gravity so body movements that stimulate the receptors for static equilibrium include tilting the head so that might be looking down at your lap as well as linear acceleration and deceleration uh deceleration examples of when static equilibrium is required is when you're moving up and down in an elevator or you're in a car that is speeding up or slowing down as you can tell from those examples static equilibrium is most often required when the body is static or at rest or in a static position and is essential for activities like standing upright for sitting and maintaining a steady gaze the urical within our VES primarily detects horizontal movement and changes in head orientation The Saul is more sensitive to Vertical movements now our semicircular canals are these parts here so again our semicircular canals make up part of our bony Labyrinth our semicircular ducts are these pink Parts which sit within the canals and are part of our membranous Labyrinth the semicircular ducts contain The receptors for dynamic equilibrium so our semicircular ducts contain our receptors for dynamic equilibrium and dynamic equilibrium is the maintenance of body position in response to movement when there is rotation around an Axis or a pivot point so this can include shaking your head as if you're trying to indicate no spinning around in a circle or going on something like a marrow go ground each of the three semicircular canals or ducts detects rotation in a different plane so our horizontal canal and duct detects rotation around the vertical axis so this could be shaking your head side to side the anterior and posterior canals detect rotation around the sagittal and the coronal planes so this is nodding your head like you're saying yes or tilting it to one side now taking a close look at the specific receptors and we're looking at static equilibrium here and within the utricle and the sacle in the Vesti which remember are within that membranous Labyrinth of the inner ear are thickened regions called the macula so up here in this little image the brown is our bony Labyrinth within the Vestal in our membranous Labyrinth we have our nutrical and our sacul in blue Within These two structures we have thickened regions which we call the macular so you can see the spelling of macula there now our macula consists of two kinds of cells hair cells which are the sensory receptors and supporting cells which surround the hair cells so our supporting cells are this beigy pink color down the bottom our hair cells are in blue sitting on top of the hair cells a stereocilia which are like really fine little hairs extending out the top and then one long hair cell called a kyum together our stereo cyia and our kyum are called a hair bundle so we can see that better in this image down here we have our supporting cells we have our hair cells we have our stereocilia and then there's one big long kyum and together these are called our hair bundle now these supporting cells secrete a thick gelatinous glycoprotein called the otolithic membrane and this rests on top of the hair cells and surrounding the hair bundle on top of this otolithic membrane is a of calcium carbonate crystals which are called Auto liths so sitting within the macula which sit within our utricle and our sacle are our supporting cells and then our hair cells sitting on top of and surrounding those hair bundles and hair cells is our autoi membrane sitting on top of that membrane is our Auto liths so those crystals now if you for example tilt your head forward so have a look at your lap or if you're in a car and it accelerates these autoliths will fall forward or they'll lag behind and when they do this they drag that autol lithic membrane with them when that autol lithic membrane moves it bends those hair cells within the hair bundle and depending on the direction of the bending will either cause depolarization or hyperpolarization of those hair cells which can also be classified as mechanically gated ion channels so when the hair cells Bend one way it will cause depolarization when they bend the other way it will cause hyperpolarization and this is what allows us to differentiate movement in different positions or different directions now in our three semicircular canals are our three semicircular ducts which make up part of our membranous Labyrinth and at the bottom of each duct is a thickened or dilated region which we call the ampulla within the ampula is a small elevation called the cryst now similar to the macula each cryst contains a bundle of hairy it contains supporting cells and extending out of those hair cells we have stereocilia and kyum which again combined are called the hair bundle so our beigy pink are our supporting cells the blue again are our hair cells and you can see our hair bundles sticking out here now covering the crystal is a mass of gelatinous material called the cup cular the hair bundles will extend into that cular also within this semicircular duct is endolymph which remember is a fluid so if we're spinning around in a circle or we're shaking how ahead no this endolymph or the fluid in our semicircular duct is going to move but it's going to lag behind a bit this will drag the capula with it which Bend these hair cells which again causes either depolarization or hyperpolarization depending on the way that that cul moves when we have the depolarization or the hyperpolarization of these hair cells it generates a receptor potential this then travels along the vestibular branch of our vestibular cckar nerve or our cranial nerve eight so a bit of a recap the vestibular and semicircular canals in the inner ear house The receptors for equilibrium the VES which contains the utricle and the sacul monitor static equilibrium so this is activated when you tilt your head or you're moving in a linear fashion or a straight line the semicircular canals and the semicircular ducts within those canals monitor dynamic equilibrium and this is activated by movement in a rotational fashion looking at static equilibrium specifically and within the Bony Labyrinth of the VES are the SACU and the utricle within the walls of the sacle and the utricle are thickened regions called macula the macula contain hair cells and and supporting cells sitting on top of those hair cells is the oolithic membrane sitting on top of the otolithic membrane is the autoliths tilting the head or accelerating or decelerating causes those ooliths to move or fall forward or back this movement drags the oolithic membrane bends the hair cells and causes a receptor potential for dynamic equilibrium and our semicircular ducts sit within the Bony semicircular canals at the base of each duct is an enlarged or a thicken region called the ampula within each ampulla is a small elevation called the crystal extending out of the chista are also hair cells which is surrounded by that gelatinous capula as the head moves so do the hairs and the cul but the endolymph or the fluid in the semi semicircular Ducks will lag this causes the movement of the Cula the bending of the hair cells and the generation of another receptor potential for both our static and our dynamic equilibrium this receptor potential we'll move along the vestibular portion of our vestibular cckar nerve and then eventually back to the brain