Auditory System Physiology Flashcards
(46 cards)
Energy Transducer
-Energy has to be converted from acoustic energy: TM is transducer
-Transduction of sound from acoustical to mechanical energy: outer to middle ear
-Transduction of mechanical energy into hydraulic (fluid in scala vestibuli) energy: middle to inner ear, oval window transducer
-Transmission and interpretation of electrochemically produced signal: inner ear to hair cells in scala media
Generally: What does the outer ear do?
collects sound
Generally: What does the middle ear do?
-provides match between low impedance of air and high impedance cochlear fluid:
-air is less dense than fluid
-hearing underwater is how we would hear if we didn’t have the middle ear
Generally: What do the hair cells do?
convert hydraulic energy to chemical-electrical energy
Generally: What does the organ of corti do?
-break sound into frequency, intensity, and temporal components
-At the organ of corti is when sounds start to get broken down and further refined
Generally: What does the VIII nerve and brainstem pathways do?
-initiates processing and transmits sounds
Generally: What does the cortex do?
-puts individual components together
-provides speech interpretation and linguistic processing
Outer Ear: Pinna
catches sound and directs sound down canal to tympanic membrane
Outer Ear: Resonant Frequency
-the frequency that is best conducted through a space or medium based upon its physical characteristics
-Concha: 5000 Hz
-Canal: 2700 Hz, high frequencies provide the understanding of speech sounds
Middle Ear
-2 cubic cm
-Impedance (resistance) matcher between air (outer ear) and fluid (inner ear)
-Without Middle Ear all have conductive HL
Remember: Middle Ear
-Pars tensa responsible for transmitting sound: tenser things transmit sound better like a drum
-make up 2/3 of TM: bottom part
-TM approximately 90 mm squared
-approx. 60 mm squared of TM are responsible for processing sound
Overcoming Impedance Mismatch: Aerial Difference
-Size difference between TM and oval window
-Same amount of sound pressure hitting the TM has to get squished down into the oval window resulting in increased force/pressure
-TM
-60 mm squared
-Oval window
-3 mm squared
-Approx. 20 times difference
-Intensity increase between 14-25 dB
Overcoming Impedance Mismatch: Lever Principle
-Lever developed between manubrium of malleus and long crus of stapes
-Manubrium approx 2X longer than long crus of stapes: fulcrum where incus and malleus connect
-Results in doubling of sound pressure
Impedance Matching Equation
-2 (lever principle) X 15 (aerial difference) = 30 dB increase
Inner Ear
Stapes displaces fluid in cochlea like hands makes waves in water
Stapes and Round Window
-Cochlea encased in bone and placed in temporal bone petrous bone
-Without round window stapes would not move: fluid unable to move
-Round window bulges out when stapes pushes on oval window and moves fluid, push (oval window)/pull (round window)
-Reciprocal action between oval and round window
-Stapes sitting in oval window converts mechanical energy to hydraulic energy
-Rocks in oval window creating waves in cochlear fluid
Stapes and Characteristics of Fluid Waves
-Characteristic of waves dependent on how stapes moves
-lower frequencies the stapes moves further than for higher frequencies
-greater force higher amplitude but frequency is not changing
-Determines location wave raise or lower on Reissner’s membrane: high frequencies fall lower on membrane because frequency is greater
Fluid Displacement
-Reissner’s membrane movement displaces fluid in scala media which then moves basilar membrane and displaces fluid in scala media
-Fluid movement in scala media moves organ of corti, tectorial membrane, basilar membrane
-Basilar membrane movement displaces fluid in scala tympani
-move round window membrane
Cochlear Hair Cells
-Outer: 3 rows
-Inner: 1 row
Cilia Sheared
-Tectorial membrane and basilar membrane move at different times because the tectorial membrane is a gel and lags behind, which causes the cilia to bend
-The way the cilia moves depends on what they do
Outer Hair Cell Movement
-embedded in tectorial membrane
-sheer relative to basilar membrane
Inner Hair Cell Movement
-not embedded in tectorial membrane so moves because of fluid
-turbulence at point of max excursion causes cilia to bend like seaweed in ocean
Hair Cell Excitatory Function
-Cilia bend toward tallest one
-initiates transmission along auditory pathway: opens door, positive ions in, cell stimulated
-influx the positive ions: depolarize
Hair Cell Inhibitory Function
-pumping out more positive ions making the cell more negative.
-Further from depolarization stage
-reduces transmission along auditory pathway
-pumps out positive ions
-hyperpolarize: more negative than resting
