The Ear External Ear outer Auricle pinna lobule ear lobe and helix harder cartilage External Auditory Canal direct soundwaves towards middle inner ear o Contain sebaceous glands which produce ear wax o Tube for ear cleaning is inserted here Tympanic Membrane ear drum boundary between external and middle ear Middle Ear Bony Ossicles direct soundwaves 1 Malleus articulates with the tympanic membrane 2 3 Stapes covers oval window Stapedius and Tensor Tympani Muscles Incus articulates with malleus and stapes protect us from loud sounds dampen the noise o Protection from sustained loud sounds not sudden ones gun shot Pharyngotympanic auditory tube links middle ear with pharynx o Releases and equalizes pressure o Ear infections otitis media common in children Auditory tube is smaller in children easily infected tube will fill with bacteria fluid etc causing infection o Rupture in ear drum will alleviate ear infection pain Babies yelling screaming alleviates their ear aches Internal Ear also called labyrinth because of complex series of canals Outer bony labyrinth encloses inner membranous labyrinth Membranous labyrinth filled with endolymph contains more potassium Bony Labyrinth filled with perilymph this surrounds membranous labyrinth Bony Labyrinth divided into 3 parts cochlea vestibule semicircular canals 1 Cochlea which are passed on to the brain hearing converts sound pressure impulses from outer ear into electrical impulses Bony chamber and membranous chamber spiral Cochlear Duct small membranous sac contains endolymph Contains organ of corti hearing receptors these receptors are mechanoreceptors and detect 2 movements fluid movement and hair cell movement Scala Tympani below cochlear duct contains perilymph Scala Vestibuli above cochlear duct contains perilymph purpose of these is to convert the movement of air that causes the tympanic membrane and ossicles to vibrate to movement of liquid and basilar membrane Filled with endolymph movement is conveyed to the organ of corti Vestibular Membrane between Cochlear Duct and Scala Vestibuli Spiral Organ organ of corti Tectorial Membrane above Basilar Membrane below Hair cells contain small projections which are embedded in these membranes Helicotrema portions where Scala Tympani and Scala Vestibuli are continuous Cochlear Implant causes movement in hair cells or stimulation of nerves o May sound a bit off need to relearn what sounds sound like Properties of Sound Tuning fork strike from one side causing areas of high and low pressure o Ear converts to vibrations causing movement within ear causing sound o The higher the frequency Hz the higher the pitch the higher the sound o The higher the amplitude dB the higher the sound Anything above 90 dB causes damage above 120 dB causes pain Transmission of Sound 1 Sound waves vibrate tympanic membrane 2 Auditory ossicles vibrate pressure is amplified 3 Pressure waves created by stapes pushing on oval window move through fluid in scala vestibuli 4 Option 1 sound with frequency below hearing travel through helicotrema and do not excite hair cells 4 Option 2 sounds in hearing range go through cochlear duct vibrating basilar membrane deflecting hairs of inner ears bending of hair cells produces sound Basilar membrane moves because of displacement of perilymph and endolymph Each region of the basilar membrane is tuned for different frequencies Depending on high or low frequency different message is sent to brain Tuned for particular pitch sound frequencies cross membrane at different locations o High tuned base of membrane toward oval window o Low tuned apex of membrane near round window o Medium tuned middle of membrane Transduction Pressure waves into electrical signals basilar membrane moved Primarily through Inner Hair Cells Projections stereocilia Longest projection kinocilium contain template proteins connected to ion channels o Bending towards kinocilium causes depolarization of cell The hair cell itself does not cause action potential the influx of ions Ca2 and K through ion channel causes depolarization of cell which causes receptor potential Ca2 ions trigger release of neurotransmitter usually glutamate o Neurotransmitter binds to 1st order neuron causing action potential Transduction within hair cells Inner hair cells send info sensory Outer hair cells receive motor impulses from brain adjust sensitivity of inner hair cells Otoacoustic emission testing for hearing in newborns lets us know whether or not ear is Dampens motion functioning properly Pathway of Sound Action Potential Some synapses in brain stem Medulla Pons Midbrain Thalamus Cerebral Cortex some crossover occurs at pons at crossover brain gets information from both sides allows us to localize where sound is coming from On test Dr Newlin will be putting more localized areas medial geniculate nucleus in thalamus etc as answers but you only need to know the general area because she won t be putting multiple thalamus answers multiple medulla answers etc 2 Vestibule Saccule contain macula vertical equilibrium Utricle contain macula horizontal equilibrium Macula move with head movement head tilted forward macula will slant Saccule and Utricle make up otolith involved in linear motions vertical and horizontal Activation of Maculae HAIRS ARE MECHANORECEPTORS 1 Nerve impulses generated in vestibular fiber 2 If hairs bend towards kinocilium causes depolarization of cell exciting nerve fiber which generates more frequent action potentials If hairs bend away from kinocilium hyperpolarization occurs Nerve fiber is inhibited and action potential frequency decreases 3 3 Semicircular canals crista ampullaris rotational diagonal movement Lateral posterior anterior canals Equilibrium Equilibrium is a function of the inner ear controlled by vestibular apparatus saccule and utricle and 3 semicircular canals Static equilibrium state of balance due to force of gravity Dynamic equilibrium maintenance of balance during sudden movements Utricle and Saccule otolithic Hair cells embedded in membrane Otoliths crystals embedded in membrane increases weight increases inertia To bend hair cells motion with the force of gravity The hair lags which causes sense of movement Semicircular Canals contain ampulla Crista ampullaris equilibrium structure for canals Located within each canal 3 o Oriented in different positions in canals allowing rotational motion detection Cupula gelatinous membrane within crista ampullaris o Hair cells projected into cupula o
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