having now covered equilibrium learning objective number three moves on to The receptors for hearing as a bit of an overview hearing is a physiological process through which sound waves are detected transmitted and interpreted by the brain it begins when sound waves enter the outer ear and travel through the external auditory canal to the tanic membrane causing it to vibrate these vibrations are then transmitted through the middle ear via the oses to the inner ear in the inner ear the vibrations called fluid in the ccka to move stimulating hair cells along the colean membrane these hair cells convert the mechanical energy of the sound waves into electrical signals which are then transmitted via the auditory nerve to the brain stem and ultimately the auditory cortex in the brain so the input for hearing occurs in the form of sound waves the characteristics of the sound waves and how they stimulate the fluid and the hair cells in the ccka allow us to distinguish different sound characteristics for example the frequency of a sound wave or how closely the high and low regions are spaced together determine its pitch the higher the frequency or the closer the waves are together the higher the pitch the greater the amplitude or the size of the sound wave the louder the sound with sound intensity or loudness measured in Deb now before we take a look at the receptors a little bit more detail about how the sound waves reach the receptors in the ccka and so to begin the sound waves are directed into our external auditory canal by the oracle the sound waves strike our tanic membrane and the membrane begins to vibrate back and forth in response to these waves the middle of the tanic membrane is attached to our malas and the malus inkies and stapes pass on these vibrations to the inner ear the vibrations at the oval window are 20 more times vigorous than those at the tanic membrane due to the simplifying effect of these three oses the movement of the stapes at the oval window creates fluid pressure in the Peril lymph of the ccka we have Peril lymph in this section here and in this bottom section here as the oval window bulges forward it pushes on that par lymph or the fluid and that movement of the fluid moves all the way around to the round window which now bulges into the middle ear so that this fluid has somewhere to go now the pressure waves or the movement of the fluid in this top section which is called the Scala vestibuli causes movement of the vestibular membrane which is a membrane which runs just along this section here the movement of the vest membrane causes movement of the endolymph inside the cocka duct so this is our cocka duct here and the movement of this vestibular membrane causes movement of the endolymph for the fluid within that cck duct and then that movement of the endolymph or the fluid inside the cckar duct causes movement of the basila membrane which a runs along this section here now our hair cells of the organ of Cy which is also called the spiral organ and is our specific receptor for hearing sits along this basil membrane here so recapping all of that for you before we go on into any more detail we have sound coming through the Oracle in through the external auditory canal to our tanic membrane that membrane vibrates in response to the sound waves and transmits those vibrations across into our three oses these oses amplify this vibration our stapin which is our last osle connects to our oval window it passes these vibrations into the paril lymph in these sections along here as that fluid moves it must have somewhere to go so the round window and the membrane covering the round window will bulge a little bit into our middle ear the movement of the Peril lymph in this section here will cause movement of the vestibular membrane which sits along the top of this red section here the movement of that vestibular membrane causes movement of the endolymph within the ccka duct movement of the endolymph causes movement of this basil membrane and extending out of our basil membrane is our hair cells which make up the organ of Cy and our receptor for hearing now I am going to recap all of this in text for you but before I do that we need to take a bit of a closer look at the cocka and those three channels that run inside the ccka and so we have that Top Channel which is the Scala vestibuli the bottom Channel which is our Scala tan both of these channels contain the per lymph these channels are actually continuous with one another our middle channel is our cocka duct and our cocka duct contains endolymph so as the soundways travel through the external ear and the middle ear to that oval window where the vibrations of the oses cause vibrations of the membrane covering the oval window this causes pressure waves to form in the Peril lymph in our Scala vestibuli and our Scala tan the movement of this Peril lymph in the scal of vestibul or this Top Channel causes movement of the vestibular membrane so our vest tibular membrane sits along here which in turn causes pressure waves or movement of the endolymph within our ccka duct so that's this middle channel here movement of the endolymph within our duct causes movement of our basil membrane so basil membrane runs along here our basil membrane contains the hair cells which make up the organ of Cy and is our receptor for hearing now when the basil membrane moves it causes hair cells that extend out of that basil membrane to bend up against our Toral membrane so this white part here is our tectorial membrane because the hair cells are bending up against this Toral membrane they will bend and a receptor potential will be generated so zooming in once small now we're going to take a bit of a closer look of this organ of Cy which is our specific receptor for hearing and so movement of the endolymph within that cocka duct which is the middle Channel causes our basil membrane to move movement of the basil membrane causes our hair cells or our stereo stelia to also move these hair cells then bend up against our tectorial membrane when these hair cells Bend our receptor potential is generated and this now runs along the ccka branch of our vestibular ccka nerve so our basil membrane moves in response to movement of that endolymph that causes movement of these hair cells that bends the stereocilia or the tiny little hair cells up against our Toral membrane that bending causes the receptor potential to be generated so putting all of that together in a written summary sound waves are directed into the external auditory canal via the Oracle sound waves strike tanic membrane causing vibrations vibrations transmitted from the tanic membrane through the oses they amplify by up to 20 times through the oses vibration of the stapes which is that last osle bone at the oval window causes movement of peril lymph in the Scala vestibuli movement of peril lymph continues to the Scala tempani which now pushes up against the membrane of the round window movement of peril lymph in the Scala vestibuli who are now back in that Top Channel causes vibration or movement of the vestibular membrane vibration of the vestibular membrane causes movement of the endolymph within the duct which is that middle Channel movement of endolymph in the cocka duct causes vibration of the basil membrane vibration or movement of the basila membrane bends up the hair cells against the Toral membrane and bending of the hair cells generates the receptor potential now lastly once a generator potential is is generated from either the hair cells in our semicircular canals or the vble or the organ of quy they then sinaps with a first order of sensory neuron and the combined graded potentials or action potentials will travel along our vestibular cckar nerve or our cranial nerve number eight so just wanted to point out that from our semicircular canals and our vable so carrying the sensory information about equilibrium these impulses travel along the vestibular branch of the vestibular ccka nerve so that's this section here coming from our semicircular canals and our vestile from the organ of Cy the nerve impulses travel along the cckar branch of the vestibular cckar nerve and so that is this section here eventually that nerve combines and then it goes off to the various regions of the brain