The inner ear also contains the vestibular organs that are responsible for balance and position. This activity produces an action potential that is propagated along the cochlear nerve and along auditory pathways, where it eventually reaches the cochlear nuclei located in the brainstem. Movement of the kinocilia triggers depolarization of the hair cell, leading to an influx of calcium and the release of specific neurotransmitters that act at the cochlear ganglion. Vibrations transmitted to the tectorial membrane cause displacement of stereocilia, leading to the displacement of the adjacent kinocilia. The hair cells have projections known as stereocilia and kinocilia that are in contact with the tectorial membrane. It contains 15000 inner and outer hair cells that are arranged tonotopically throughout the cochlea to help distinguish between sounds of varying frequencies. The organ of Corti is located within the scala media and is responsible for converting mechanical forces into electrical impulses. The compression of the scala media causes the tectorial membrane to change the position of cells within the organ of Corti. Within the scala media, there is a tectorial membrane that sits atop the organ of Corti. The presence of the round window allows for fluid to move more freely through the cochlea, thereby improving sound transmission.Īs vibration transmits across the oval window, perilymph gets pushed towards the cochlear apex, which causes the scala media to become compressed. Rather, the round window membrane is located inferomedial to the oval window and functions to counteract the fluid shift created in the cochlea. In contrast to the oval window, the round window does not articulate with the stapes. The perilymphatic wave terminates at the round window, another point at which the middle ear communicates with the inner ear. Vibrations across the oval window initiate a perilymph wave that propagates along the scala vestibuli, with high frequency sounds dissipating earlier at the base of the cochlea and low-frequency sounds dissipating later towards the apex of the cochlea. Vibration from the stapes gets transmitted through the oval window, which is an opening into the inner ear through which the middle and inner ear communicate. The difference in concentration of potassium ions among the three fluid compartments within the cochlea enables proper transduction of current along with the hair cells. ![]() This difference in concentration allows for a positive endocochlear potential. Endolymph is rich in potassium and low in sodium and calcium, whereas perilymph is rich in sodium and low in potassium and calcium. Endolymph and perilymph vary significantly in their concentration of ions, which is essential to the overall function of the cochlea. The perilymph in the scala vestibuli originates from blood plasma, whereas the perilymph in the scala tympani comes from CSF. The endolymph within the scala media originates from cerebrospinal fluid (CSF) and is secreted by the stria vascularis, which is a network of capillaries located in the spiral ligament. The scala vestibuli and scala tympani both contain perilymph and surround the scala media, which contains endolymph. The cochlea contains three distinct anatomic compartments: the scala vestibuli, scala media (also referred to as the cochlear duct), and scala tympani. The cochlea is a spiral-shaped fluid-filled organ located within the cochlear duct of the inner ear. The membranous labyrinth contains a fluid known as endolymph, which plays a vital role in the excitation of hair cells responsible for sound and vestibular transmission. These organs make up the membranous labyrinth that is within the bony labyrinth, separated only by perilymph. The inner ear is located within the bony labyrinth of the temporal bone and contains the cochlea, semicircular canals, utricle, and saccule. ![]() Vibrations are transmitted from the malleus through the incus to the stapes, which is in contact with the cochlear oval window. The middle ear is an air-filled space that contains the three ossicles (malleus, incus, and stapes), which are bones responsible for transmitting vibrations from the tympanic membrane to the inner ear. The outer ear consists of the pinna, external auditory canal, and tympanic membrane and is responsible for the transmission of sound waves from the external environment. The ear is organized into three different anatomical structures: the outer, middle, and inner ear.
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