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You are watching: As sound levels increase in the spiral organ (of corti), ________.

StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Anatomy, Head and Neck, Ear organ of Corti

Hunter J. White; Muhammad Helwany; Diana C. Peterson.

Author Information

Introduction

The body organ of Corti is an organ of the inner ear situated within the cochlea i m sorry contributes come audition. The organ of Corti includes three rows of outer hair cells and also one row of inside hair cells. Vibrations caused by sound waves bend the stereocilia on this hair cells via an electromechanical force. The hair cells transform mechanical energy into electric energy the is sent come the main nervous mechanism via the auditory nerve come facilitate audition.


Structure and also Function

The primary role of the body organ of Corti is the transduction of hear signals. Sound waves get in the ear via the auditory canal and cause vibration the the tympanic membrane. Activity of the tympanic membrane causes subsequent vibrations in ~ the ossicles, the three bones of the center ear which carry the energy to the cochlea through the oval window. Together the oval home window moves, waves carry to the perilymph liquid inside the scala tympani and also then the scala vestibule that the cochlea. When fluid moves with these structures, the basilar membrane (located between the scala media and also scala tympani) move respectively come the tectorial membrane (Figure 1A).

The body organ of Corti is an body organ of the inside ear contained within the scala media of the cochlea (Figure 1A). It resides on the basilar membrane, a stiff membrane separating the scala tympani and scala media (Figure 1A). The scala media is a cavity within the cochlea that contains endolymph which has a high (150 mM) K+ concentration. The endolymph help to manage the electrochemical impulses that the auditory hair cells.<1> 

The body organ of Corti is created of both sustaining cells and also mechanosensory hair cells. The plan of mechanosensory cells are right into inner and also outer hair cells follow me rows (Figure 1B). Over there is a solitary row of inside hair cells and also three rows of outer hair cells which are separated by the sustaining cells. The sustaining cells are likewise named Dieters or phalangeal cells.

The hair cells within the organ of Corti have sterocilia that affix to the tectorial membrane. Shifts in between the tectorial and also basilar membranes move these sterocilia and activate or deactivate receptors on the hair cell surface. Once cation channels open on the hair cells, potassium ions flow into the hair cells, the cells depolarize, and also the depolarization causes voltage-gated calcium channels to open. The calcium influx results in glutamate release from the hair cell onto the listening nerve. The auditory nerve then sends out information around the sound tide to the brain.

Inner hair cells duty primarily as the sensory organs because that audition. They provide input come 95% that the auditory nerve fibers that job to the brain.<1> The stiffness and also size of the hair cell setup throughout the cochlea permit hair cell to respond come a range of frequencies from short to high. Cells at the apex to respond to lower frequencies when hair cell at the base of the cochlea (near the oval window) answers to greater frequencies, which create a tonotopic gradient throughout the cochlea.<2><1> 

While inner hair cells space the output facility of the cochlea, the outer hair cells room the input center. They receive descending inputs from the mind to help with the modulation of within hair cell duty (i.e., modulating tuning and intensity information). Unlike various other regions of the brain, the modulation of within hair cell by outer hair cells is not electrical but mechanical. Activation of outer hair cells alters the stiffness of their cell bodies; this manipulates the resonance the perilymph fluid movement within the scala media and enables for fine-tuning of inner hair cabinet activation.<1>

Inner and outer hair cells space distinctly different in structure. Both varieties of hair cells have actually stereocilia top top the apical surface; however, the setup of sterocilia and their connection to the tectorial membrane room distinctly different. For both varieties of hair cells, the mechanical bending that the sterocilia opens up potassium channels at the advice of the sterocilia that allow hyperpolarization of the cells.<1> The tallest the the stereocilia of external hair cells are embedded into the tectorial membrane. This stereocilia obtain displaced together the basilar membrane moves v the tectorial membrane. The stereocilia of inside hair cells are free-floating. Activity of the viscous perilymph liquid provides the mechanical pressure to open up these channels.<1> 

Inner hair cell activation is lot more complex than external hair cabinet activation. The motion of fluid within the scala media depends on the resonance (vibration) that both the tectorial membrane and also organ of Corti. Cell within the body organ of Corti room much more flexible 보다 cells within the basilar membrane. Alterations in the stiffness of this cells adjust the resonance the the organ of Corti and also subsequently the movement of fluid within the scala media.<1> 

The external hair cells change the stiffness that the body organ of Corti v a motor protein, prestin, located on the lateral membrane of these cells. This proteins vary in shape in an answer to voltage changes. Depolarization that the outer hair cells reasons prestin come shorten, moving the basilar membrane and also increasing the membrane deflection, thereby intensifying the result on the inside hair cells.<3><4><5><6>


Embryology

The inside ear originates from the invagination that the otic placodes during the fourth week that development. The otic placodes room sensory placodes, which space a collection of transiently thickened surface ar ectodermal spot that kind pairs rostrocaudally in the head an ar during week 4 of development. Sensory placodes are connected in the advance of special sensory systems favor vision, olfaction, and also hearing. The otic placodes are among the very first sensory placodes to kind and contribute to the development of the within ear structures connected with hearing and also balance. Otic placode induction is dependency on Wnts and FGFs noted by the hindbrain and also surrounding head mesenchyme. The otic placodes are situated behind the 2nd pharyngeal arch and also give increase to the otic pits through invaginating right into the mesenchyme adjacent to the rhombencephalon during the 4th week the development. Towards the end of the 4th week, the otic pits break turn off from the surface ar ectoderm to kind a hole piriform shaped framework lined with columnar epithelium referred to as the otic vesicle. At this point, the otic vesicle lies beneath the surface ar ectoderm covering in the mesenchyme, forming the otic capsule. The statoacoustic ganglion additionally forms during the development of the otic vesicle and also splits right into cochlear and vestibular portions. The otic vesicle differentiates to form all the contents of the membranous labyrinth and ultimately gives rise to the inner ear structures connected with hearing and also balance. As the otic vesicle establishes into the membranous labyrinth, the epithelium undergoes variations in thickness and begins to distort. The otic vesicle divides into a dorsal utricular section and ventral saccular portion, through the dorsal utricular part giving increase to the vestibular system and also the ventral saccular portion giving increase to inside ear structures prefer the body organ of corti that are affiliated in hearing. The ventral saccular part develops right into the cochlear duct (which homes the organ of corti) and saccule. The dorsal utricular portion forms right into the utricle, semicircular canals, and endolymphatic tube.

In the 6th week that development, the ventral saccular ingredient of the otic vesicle penetrates the neighboring mesenchyme in a spiraling fashion. The completes two and a half turns to form the cochlear duct through the finish of the 8 hours week. In ~ this point, the saccule connects to the utricle via the ductus reuniens and also mesenchyme surrounds the entire cochlear duct. The mesenchyme surrounding the cochlear duct forms cartilage. During the tenth mainly of development, this cartilaginous covering undergoes vacuolization to produce the two perilymphatic spaces that the cochlea, the scala vestibule, and the scala tympani. Two membranes different the cochlear duct proper, i beg your pardon is likewise known as the scala media, indigenous the scala tympani and also scala vestibule. The basilar membrane demarcates the scala media indigenous the scala tympani, when the vestibular membrane separates the scala media native the scala vestibule. Laterally, the cochlear duct is attached to the bordering cartilage via a connective tissue structure called the spiral ligament. The body organ of Corti is situated within the scala media the the cochlear duct and also resides ~ above the basilar membrane. The capsular cartilage that surrounds the membranous labyrinth becomes ossified between 16 and also 23 weeks gestation to kind the true bony labyrinth. The body organ of Corti is the sensory section of the cochlear duct located in between the scala media and also scala tympani. There is one row of inner hair cells and also three rows of outer hair cell which are surrounded by supporting cells. Inner and also outer hair cells form, differentiate, and also separate right into their respective rows before the formation of the Deiters or supporting cells. Number of genes share web links with the embryological advance of the body organ of Corti. Cochlear duct growth and also hair cell development have specifically been attached to figured out genes. In regards to neural development, the spiral ganglion, which innervates the organ of Corti, creates from the primitive otocyst coming before the organ’s development.<7>


Blood Supply and also Lymphatics

The labyrinthine artery is the key supplier that oxygenated blood to the cochlea and also therefore the body organ of Corti. This artery is likewise known together the listening artery or internal auditory artery. The labyrinthine artery most commonly originates from the anterior inferior cerebellar artery (AICA). AICA most frequently originates indigenous the basilar artery. Occasionally, around 15% that the time, the hear or labyrinthine artery, deserve to branch off directly from the basilar artery. Much less commonly, this artery might originate from the remarkable cerebellar or vertebral artery.

The labyrinthine artery follows the vestibulocochlear nerve from its suggest of origin into the internal acoustic meatus wherein it additional divides right into two branches, the anterior vestibular artery, and the usual cochlear artery. The usual cochlear artery will then divide right into two an ext arteries, the suitable cochlear artery, and the vestibulocochlear artery. The vestibulocochlear artery then provides off the vestibular ramus and the cochlear ramus.<8><9>


Nerves

Inner hair cells room mechanoreceptor cells. Castle transmit information around acoustic stimuli straight to the type I spiral ganglion neurons (i.e., hear nerve, radial afferents). This afferents synapse in ~ the cochlear nucleus within the brain. Input from the inner hair cell to the form I spiral ganglion neurons deserve to be transformed by lateral olivocochlear efferent nerves that have axodendritic synapse onto these form I ganglion neurons. The lateral olivocochlear nerves execute not synapse top top inner hair cells. They end on the listening nerve fibers in ~ the cochlea.<10><1><11>

Outer hair cells have actually both efferent and also afferent connections. They obtain input from medial olivocochlear neurons directly onto your cell bodies, axosomatic synapses. This efferent connections form feedback loops the manipulate the stiffness of the organ of Corti and therein the activity of the within hair cells. The outer hair cells synapse onto kind II spiral ganglion neurons.<1><11> The role of this afferents is tho unknown. These neurons do not respond come auditory stimuli.<1>


Physiologic Variants

Individual sport exist in regards to the size and shape of the cochlea. These variations can have wide-ranging effects on operation outcomes.

Common sports include:


Surgical Considerations

Electrode variety placement into the cochlea is a current treatment choice for high-grade sensorineural hearing loss. Operation complications space typically connected with surgical an approach or an equipment failure. Symptom classify together either young or major. The most usual minor complication consists of infections, vestibular problems, and also tinnitus formation. Major complications include more serious infections, damages to center or inner ear structures, and an equipment failure problems.<14> These species of complications have reduced over the years v the usage of small surgical incisions, the development of smaller implants, and the usage of an ext biocompatible implants.<15>

During electrode variety surgery, surgeons need to be conscious of the ar of the petrous section of the internal carotid artery and the jugular bulb. These frameworks lie close to the tympanic cavity and should be avoided throughout surgery. Although not common, anatomical variations because that both of these structures happen including the lack of the bone dividing these vessels and the middle ear and also positioning the one or much more vessel in one of two people a exceptional or lateral direction from normal. Throughout surgery, this structures deserve to be damaged, or damage may occur due to post-surgical inflammation. To stop these complications, CT or MRI imaging the the an ar should it is in performed prior to surgery to determine anatomical abnormalities. If imaging discover anomalies, surgery within the tympanic cleft need to be avoided.<16>


Clinical Significance

Sensorineural hearing lose is the most typically reported cause of listening deficits. This kind of hearing loss regularly results native exposure come either loud sounds or ototoxic drugs. Exposure to according to noises reasons the vibrational shift between the tectorial and basilar membrane to increase. This transition can damages the stereocilia that the outer hair cells. When damage occurs to the outer hair cells, the stiffness of the organ of Corti reduce which in turn increases vibrational forces on the inner hair cells. Damage to the outer hair cells decreases the security of inside hair cells and also causes them to become much more sensitive. End time, the inside hair cell will also become damaged and also audition affected.

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Aminoglycoside antibiotics are an instance of ototoxic drugs. This drugs space K+ channel blockers. Together such, they block the ability of both inner and also outer hair cells to depolarize. These varieties of drugs can also adjust the concentration of ion within the perilymph which can lead to damage or death of both inner and outer hair cells; destruction of the hair cells causes permanent auditory deficits due to the fact that they do not regenerate.<1>