Histology Ear

External Ear
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Terms in this set (71)
wax formainon in the ear occurs due toexcessive activity of ceruminous glandsTympanic membrane external surface covered byepidermisTympanic membrane internal surface covered bycuboidal epitheliumtympanic cavitylocated in the petrous temporal bone and is separated from the external auditory canal by tympanic membraneSound waves in middle earimpinging on the tympanic membrane are converted into mechanical vibrations which are then applified by a system of lever made up of 3 small bone called ossicles and transmitted to the fluid-filled inner ear cavitythe ossicles articulate with one another viasynovial jointsOssiclesmalleus, incus and stapesthe middle ear cavity communicates anteriorly with the nasopharynx via theauditory (Eustachian) tubeinterconnected air spaces which lighten the mass of theMastoid part of the temporal boneMiddle ear is lined bysimple squamous or cuboidal epitheliumBony ossicles roles:they modulate the movement of the tympanic membrane, they apply force to the oval window, thus amplifying the incoming sound wavesinherited disease resulting in abnormal growth of bone near the middle earOtosclerosis(middle ear infection) affect the movements of the ossicles, and are conditions leading to hearing lossOtitis MediaBarotraumamiddle ear changes due to changes in atmospheric pressureinner ear occupiesosseous labyrinth within the petrous portion of the temporal boneosseous labyrinth contains themembranous labyrinth, a structure that houses both the vestibular and auditory systemVestibular system components:two sacs (utricle and saccule) three semicrcualr canals.membranous labyrinth containendolymphendolympha fluid with a high concentration of K and a low concentration of NaPerilymphwith a high na and low k content present between the membranous labyrinth and the walls of the osseous labyrinthperimembranous space is directlyconnected with the subarchnoid space and like the latter is crossed by delicate fibrous strands and lined with sqaumous epitheliummembranous labyrinth is lined bya simple epitheliumSemiciccular canalsrespond to rotational movememnts of the heand and body (angular accelerationsmaculae in saccule and utricle respond totranslational movements (linear acceleration)vestublar organ innervated byvestibulocochlear nerve (cranial nerve VIII)labyrinthine artery supplieslabyrinthstylomastoid artery suppliesblood to the semicircular canalsCrista ampullaris consists ofsensory epithelium covered by gelatinous mass called the cupulaSensory epithelium consists of two cell typeshair cells, the supporting cellshair cells occupya recess in the apical region of the supporting cells and do not reach the basal laminawhen the position of the cupula changes in response to movements of the endolymphit causes displacement of the sterocilia and kinocilium of the hair cellswhen the stereocilia move toward the knociliumthe plasma membrane of the hair cells depolariezes (excitation)when sterocilia are deflated away from the kinociliumthe hair cell hyperpolarizes and afferent nerve fibers are not stimulated inhibitionwhen integrated, perception from 3 semicrcular canals provide info ondirection and rate of acceleration of head movementutricle and saccule display a sensory epithelium calledmaculamaculacontain hair cells and supporting cellsanterior semicircular canalis part of the vestibular system and detects rotation of the head around a rostral-caudal (anterior-posterior) axisposterior semicrcular canal is a part of the vestibular system and detects rotations of the headin sagittal planelateral or horzontal canalexternal semicrcular canal is the shortest of the three canals.Movement of fluid within this canal corresponds to rotation of head around a vertical axis (Neck)cochlear ductis a membranous coiled duct inserted in the bony cochleachochlea consists ofapex and basecochlear ductsrepresents the central chamber and contains endolymphscala vestibulistarting at the oval windowscala tympaniending at the round windowscalae vestibuli and tympaniare filled with perilymph and communicate at the helicotremaOrgan of corti is formed byinner and outer hair cells, supportin cells, the tectorial membrane, extending from the spiral limbus, inner tunnel, limited by the outer and inner pilar cells, separating inner from outer hair cells.Inner hair cellsextend from the base to the apex of the cochleaOuter hair cellsarranged in 3 parallel rowstectorial membraneis in close contact with the taller stereocilia of the hair bundlewhen the basilar membrane and organ of corti are displacedstereocilia hit the tectorial membrane and depolarization of the hair cells occurshigh concentration of K in the endolymph and the high concentration of Na in the perilymph determinean electrical potential difference. the ion concentration is regulated by the absorptive and secretory activity of the stria vascularis.Fluid movementin the scala tympani induces the movement of the basialr membrane causing the taller stereocilia to be displaced by the tectorial membrane.ion channels at the sterocilia tip open driving K into the cell which then becomes depolarizedupon depolarization, an influx of ca to the basal region of the hair cells dtermines the release of nerotransmitters at the hair cell cochlear nerve fiber synapse and generation of a stimulusconductive deafnessis caused by disorders that interfere with the conduction of sound through the outer and middle ear, affecting hearing before the sound reaches the cochlea.Otitis mediaInflammation affecting the middle ear that reults in secretions buliding up within the middle ear cavity, which usualy resolves with appropriate therapyOtosclerosisis an inherited disease where the ossicles fuse together, preventing conduction of sound. Surgery can re-establis conduction and restore hearingSensory-neural deafnessis caused by damage to the sensory receptors of the inner ear (the hair cells, organ of Corti) or the auditory nerve leading to the brainAge-related loss of high frequency hearing has been calledPresbycusisexposure to noise can causeloss of hearing due to damage to sensory elements in the organ of cortiIs an abnormality of the inner ear, clinically, affected patients experience dizziness, disturbance of balance (vertigo), a high pitched, rushing or roaring sound in the ears (tinnitus) and fluctiating hearing lossMeniere's diseaseMeniere's disease are associated with anincrease in endolymph volume within the membraous labyrinth system. An increase in endolymph volume is believed to cause the membranous labyrinth to swell. Transient dysfunction of the labyrintheine system can be caused by viral infection.