Hearing I Flashcards
What is the nature of sound?
-Sounds are audible variations in air pressure: anything that moves air molecules generates sound; speed of sound: Travels at 343 m/sec (767 mph)
-Cycle: distance between successive compressed patches of air
-Sound frequency: number of cycles of compressed air per second expressed in hertz (Hz)
–20 Hz = 20 cycles within 1 second
What are the 3 aspects of audible sound?
-Range: 20 Hz to 20,000 Hz
-Pitch: High pitch = high frequency (ex: ultra sound, > 20,000 Hz, heard by some animals); Low pitch = low frequency (ex: infra sound, < 20 Hz, heard by animals)
-Intensity (amplitude): High intensity is louder than low intensity
What are the 3 parts of the auditory system?
-Outer ear: pinna & tympanic membrane
-Middle ear: tympanic membrane & ossicles
-Inner ear: oval window & cochlea
What are the characteristics of the Outer ear?
-The outer ear is composed of the pinna that collect sounds and funnels them into the auditory canal.
-Auditory canal carries sound to our eardrum (tympanic membrane)
-The tympanic membrane vibrates in response to sound into the middle ear
What are the characteristics of the Middle ear?
-Vibration of the tympanic membrane produces movement of the ossicle in the middle ear
-The ossicles are a series of bones connected to the eardrum that transfer (and amplify) movements of the tympanic membrane into movements at the oval window (3 smallest bones)
*acts like a piston to transmit sound
What are the characteristics of the Inner ear?
-The oval window gives way to the fluid-filled cochlea
-The cochlea transfers physical motion of the oval window membrane into a neuronal response –> transduction (happens inside cochlea)
What are the three ossicles & their function (middle ear)?
-Three ossicles:
–the malleus – hammer: attached to the tympanic membrane
–the incus – anvil
–the stapes – stirrup –> footplate that acts like a piston on the oval window
-Ossicles amplify sound from air to fluid
–tympanic membrane vibrates in air, and inner ear is fluid filled (greater inertia)
–the ossicles amplify and focus an air vibration from the tympanic membrane onto the oval window
What is the Attenuation Reflex (middle ear)?
-Adapts ear to loud sounds
-Protects inner ear (continuous loud sounds)
-Enables us to understand speech better
-Attenuates the sound of our own voice
muscles around the ossicles become stiff to attenuate to loud sound and it makes the thumping less hard –> not as big of a wave = not as much damage
*this only works with loud & continuous sounds (doesn’t work with gunshot)
What are the characteristics of the cochlea (inner ear)?
-the cochlea has a spiral shape resembling a snail’s shell
-Cross section of the cochlea shows three fluid-filled chambers:
–Scala vestibuli & Scala tympani (filled with perilymph)
–Scala media (filled with endolymph)
What are the basilar membrane & organ of Corti responsible for (inner ear)?
-The basilar membrane separates the scala
tympani from the scala media (breaks down sound into its component frequencies)
-The organ of Corti sits upon the basilar membrane below the tectorial membrane (roof) (friction)
-The organ of Corti contains auditory receptors (this converts it into a signal)
How does the structure of basilar membrane determine its response to sound?
-motion from sound sends vibrations that travel along the basilar membrane from the oval window to the round window
-Structural properties of basilar membrane determine its response to sound:
–5x wider at apex (end), than at the base
–stiffness decreases from base to apex – base 100x stiffer than apex
–stiff base, wide floppy apex
-The distance the wave travels up the basilar membrane depends on the frequency of the sound
-High frequency sounds make the base vibrate a lot
-Low frequency sounds travel all the way to the apex
-The response of the basilar membrane establishes a place code
-Different locations of membrane are maximally deformed at different sound frequencies
-Systematic organization of sound frequency within an auditory structure is called tonotopy
What is the path of sound waves in Auditory Transduction?
-Sound waves move the tympanic membrane
-Tympanic membrane moves the ossicles
-Ossicles move the membrane at the oval window
-Motion at the oval window moves fluid in the cochlea
-Movement of fluid in the cochlea causes a response in sensory neurons (by causing vibration of the basal membrane and the Organ of Corti)
What are the hair cells in auditory transduction?
-Auditory receptors are called hair cells as they contain hairy looking stereocilia at their tip
-The bending of the cilia is the critical step to transduction
-Hair cells are not neurons and lack axons, they do not generate action potentials
-Hair cells synapse with bipolar neurons in the spiral ganglion –> auditory nerve
What does the organ of corti contain, and what happens when the basilar membrane moves up and down?
-The Organ of Corti contains inner hair cells and outer hair cells (approx. 3x more).
-As the basilar membrane moves up and down, the cilia bend back and forth against the rigid tectorial membrane. (where chem –> electrical transduction)
