Exam 2 Notes and Study Guide 1 What are the main parts of the ear and what is the function of each What is impedance mismatch How does the cochlea work describe the sequence of events that transform changes in air pressure to movement of the basilar membrane How does the hair cell work Some say that the cochlea does a Fourier analysis how does it do this How does bone conduction work What is the difference between a conductive and a sensorineural hearing loss a Main Parts of the Ear i Middle Ear transfer acoustic energy from compression waves in air to fluid membrane waves within the cochlea 1 Eardrum also called tympanic membrane beginning of the middle ear the membrane vibrates in response to sound waves and moves the bones of the middle ear a Must go from moving tympanic membrane in air to moving 2 Ossicles to amplify sound vibrations lever action gives some fluid in the cochlea mechanical increase in force a Hammer or malleus long arm attached to eardrum first bone to move attached to tympani muscle b Anvil or incus c Stirrup or stapes 941 321 6626 vibrates against membrane behind oval window i Size differential much smaller area of stapes on oval window than the area of the tympanic membrane increases force about 20x ii Inner Ear converts energy to a code that can be interpreted by the brain filled with fluid disrupt basilar membrane 1 Cochlea the fluid inside the cochlea passes vibrations to tin hairs connected to auditory nerves contains transducers for hearing hard walled chamber filled with fluid a Tuned to different frequencies i High frequencies displace basilar membrane in base of cochlea of cochlea ii Low frequencies displace basilar membrane in apex b unrolling of cochlea c High frequencies displace basilar membrane in base of cochlea low frequencies displace basilar membrane in apex of cochlea i Base of cochlea basilar membrane narrow and stiff ii Apex of Cochlea basilar membrane fat and floppy d Sequence of events Air movement to mechanical movement mechanical movement to fluid movement fluid movement to membrane movement membrane movement to bending of hair cell bending of hair cell to ion flow ion flow to transmitter release transmitter release to action potential in auditory nerve cochlear amplifier later e Related to Fourier Analysis the cochlea converts time dependent vibrations into signals related to frequency and the conversion from time to frequency is the basis of Fourier analysis makes a map of sound frequency f Tonotopic map measuring electrical responses from different points on the cochlea revealed that there is indeed a tonotopic map cells in different spots on the cochlea respond to different frequencies with high frequencies near the base and low frequencies near the apex 2 Vestibular System involved in balance equilibrium 3 Auditory Nerve these send messages to the brain which are then interpreted as sounds transmit information to brain brain sends to muscles in all body parts to ensure equilibrium iii Outer Ear funnel and filter sound and protect structure at end from damage 1 Auditory Canal or Ear Canal connects the outer ear with the eardrum tympanic membrane the narrow passage through which sound enters the ear 2 Pinna collects sound waves and passes them along the auditory canal to the eardrum a Pinna shapes vary quite a lot between people Filters sounds blocks some frequencies more than others Filtering depends on where the sounds are coming from Unique Head Related Transfer Function HRTF Aids is localization of elevation and in determining front back Impedance mismatch when a sound wave in air reaches liquid inner ear the wave losses about 30 dB in pressure or 99 of the power the middle ear plays a crucial role in overcoming mismatch between sound waves in the world around us and the waves that emerge in our inner ears harder to move fluid than air i The middle ear helps with two mismatch problems b 1 The eardrum is much larger than the oval window This difference allows the eardrum to move the oval window more efficiently 2 Shape of the eardrum so that it increases the force produced by the malleus which in turn increases the force at the stapes c Bone Conduction transmission of sound by a bone vibrator placed behind ear vibrator causes bones of skull to vibrate which stimulate the inner ear cochlea d Hearing Loss i Conductive hearing loss normal hearing by bone conduction but difficulty hearing signals by air conduction problem in outer and middle ear 1 Causes when the coupling is disrupted sound can t get into inner ear efficiently middle and outer ear excess ear wax blocking ear canal ear infection otitis media arthritis of ossicles ii Sensorineural hearing loss result in fairly unequal air and bone conduction thresholds problems in inner ear 1 Mainly outer hair cells that are damaged 2 Severe deafness but OHCs don t sent information to the brain 2 What are the different functions of the inner and outer hair cells How does the outer hair cell accomplish that function What causes an optoacoustic emission and what are they good for a Hair Cell cilia i Inner single row jug shaped free of attachment above cell bodies firmly encased in supporting structures that surround each inner hair cell receives afferent sensory nerves leading from ear to brain ii Outer three rows cylindrical in shape support cells at hair cell base receive efferent nerve fiber from the brain iii Hair cells are mechanoreceptors activated by mechanical movement ion channels of hair cell open when stereo cilia are bent 1 Upward phase bend toward tallest stereo cilia 2 Downward phase bend away from tallest stereo cilia b Optoacoustic Emissions sound coming from the ear canal i Caused by the motion of the cochlea s sensory hair cells as they respond to auditory stimulation ii Used for hearing screening 3 What do we mean by cochlear amplifier and how does this amplifier work a Cochlear amplifier a positive feedback mechanism within the cochlea that amplifies the traveling wave and adds a lot of energy to membrane movement i So much energy you can hear sound coming out of the ear ii Vibrations in the Organ of Corti are sensed and forced to generate iii OHC s work like frequency specific amplifier like equalizer on a stereo synchrony to increase vibrations 1 When OHCs change shape a So movement of cilia makes depolarization and depolarization makes it move 4 What is the major cause of deafness What is the difference between sensorineural and conductive hearing loss What
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