HomeArticlesCochlea – Anatomy of the Auditory System and Vestibular System | Lecturio Cochlea – Anatomy of the Auditory System and Vestibular System | Lecturio By Joseph Donaldson October 7, 2019 Articles, Blog 4 Comments Tags:Anatomy of the Auditory System and Vestibular System, Anatomy USMLE, cochlea, inner ear, Membranes, Structure of the ear, The Auditory System Related Posts Melanin theory | Wikipedia audio article Digital Eye Strain Dinosaur Song for Kids | Nursery Rhymes | Dinosaur Songs | PINKFONG Songs for Children About Author admin 4 Comments Anri Timon April 18, 2018 Wow!!!! I am from Ukraine, and i love your videos!!! Thanks God for us! Reply Nicolette Assink April 18, 2018 Transcript – For easy reading! The cochlea is the structure of the inner ear that harbors the cellular machinery of the auditory apparatus and its characteristics are very, very unique in order for it to carry out its marvelous function. And so the first thing that I want you to know about the cochlea is that it has two labyrinths and one of these is the osseous labyrinth. And so the bony canal of the cochlea is along in through here. Here's the outer bony wall of the cochlea as it spirals internally within the inner ear. And then here's the other side of that bony canal that coils within the inner ear. Running within this osseous labyrinth is a membranous component, and this is the membranous labyrinth, and we see it in blue and it too will follow the coiled nature of the bony labyrinth and then it'll end here, finally at the apex of that coiled cochlea. If we take a cross-section through the bony or osseous labyrinth and the membranous labyrinth, this is the profile that we'll see and in that profile, we will have three scala. So here is the scala vestibuli. Here's the outer portion of the osseous labyrinth. On the opposite side, we have the scala tympani and you can appreciate the bony wall of the osseous labyrinth here. And then between the scala vestibuli and the scala tympani, we have the scala media, and this is also referred to as the cochlear duct. Now, the cochlear duct has a specialized fluid called the endolymph. The scala vestibuli and the scala tympani have extracellular fluid that's termed a perilymph. The endolymph, however, is very, very unique in its ionic concentration. Normally, extracellular fluid is very, very low in potassium. However, the scala media, it's endolymph is extremely high in potassium ion concentration and this assists very greatly in the depolarization of the hair cells and reduces the ATP requirements of the hair cells as well. The endolymph is secreted by a specialized epithelium called the stria vascularis and that's shown here on this aspect of the scala media. The scalae are separated from one another by membranes. This membrane separating the scala vestibuli from the scala media and this is aptly termed in blue here, the vestibular membrane. And then the membrane that separates the scala media from the scala tympani, tympani here, media here, shaded in blue is the basilar membrane. Now, when we think about audition, the Organ of Corti within the scala media is literally the masterpiece of cellular micro architecture. This is the apparatus that's going to be responsible for taking the sound waves and converting them into action potentials. The Organ of Corti contains numerous structures, but the ones that we're most interested in are those shaded in green and these are the hair cells, the Organ of Corti. Now, these are the outer hair cells and then that this will be a row of inner hair cells and the stereocilia are embedded in the tectoria membrane that we see in through here. The hair cells in association with some supporting cells are anchored to the basilar membrane that we see down in through here, and that is labeled here for you. The cochlea along the basilar membrane is frequency tuned and what you need to understand about the frequency tuning of the basilar membrane is that high-frequency sounds will allow the basilar membrane in the base of the cochlea to start to vibrate. They are more sensitive to high-frequency sound waves and so the basilar membrane here will start to vibrate and that will cause movement of the hair cells because they're embedded in the tectoria membrane and then they'll start to depolarize in response to high-frequency sound waves. Low-frequency sound waves are going to be toward the apex of the cochlea. And at this point, that area of the basilar membrane will start to vibrate in response. And then the rest of the basilar membrane is fine-tuned again from high to low in between those areas. Now I want to guide you through the innervation of the cochlea. And so once the hair cells have become depolarized, action potentials will be conveyed along the nerve fibers that make up the cochlear component of cranial nerve number eight. And so we see an innervation here of the hair cell with a cochlear nerve fiber, and then that's running through a bony canal in through here. And we're going follow that out toward the central nervous system. Those nerve fibers will start to come together and in this area will have nerve cell bodies, those cochlear nerve afferent fibers residing within this spiral ganglion. The fibers will continue in this direction and in this view, we'll see those fibers extending away from the ganglion within the cochlear nerve itself. This is within the inner ear and so it needs to exit the inner ear to get to the central nervous system. And so it will exit through the internal acoustic meatus that we see here. And then the cochlear nerve, along with the vestibular nerve, will form cranial nerve number eight that we see in through here. NAssink Transcriptions[email protected]@gmail.com Reply Mrigendra thapa April 23, 2018 lovely video Reply Patricia Novero October 1, 2019 great video! thank you so much Reply Add a Comment Cancel reply Your email address will not be published. Required fields are marked *Comment:*Name:* Email Address:* Save my name, email, and website in this browser for the next time I comment.