Flashcards in L25: Audition Deck (22):
Sound is _________; our perception is ______________.
Sound is frequency; our perception is pitch.
Conduction of sound from external ear into the fluid filled inner ear requires a 32 fold increase in pressure to compensate for the loss in sound from conduction into aqueous medium. How do our ears work to achieve this 32 fold increase?
-there's a 20 fold difference in surface area btw tympanic membrane (60) & oval window (3), so here we achieve a 20 fold increase in pressure
-lever action of ossicular chain in middle ear external to oval window contributes to increase in pressure by 1.3 = 26 fold increase
-virtue of how tympanic membrane vibrates increases to about 29 increase in pressure.
-the other 3 db is reflected.
What is tympanometry?
clinical technique that measures impedance of the middle ear to sound
What can cause conductive hearing loss?
-otitis media, otosclerosis & ear wax build up in external ear canal.
In conductive hearing loss, more than the 3 db of sound is reflected.
(normally air conduction >/- bone conduction)
What is basilar membrane? Explain how the basilar membrane responds to applied forces along its membrane from the oval window to the apex.
it is a membrane in cochlea that has certain properties that allow different frequencies to affect it differentially.
for equally applied forces along the membrane, the apex (wider & less stiff) will experience greatest displacement (bending). Basilar membrane at oval window is more stiff than at apex.
Explain what happens as sound waves enter oval window.
-the stapes moves into oval window as sound waves come in, creating downward bulge at basilar membrane.
-the bulge moves along membrane & gets bigger b/c same force applied creates bigger displacement as width increases and stiffness decreases from oval window to apex.
-stapes will move out of oval window, creating an upward bulge as well
as sound waves move down the basilar membrane, the waves will become more in-phase or more out-of-phase?
T/F: each sound wave has its unique wave form
True, b/c each frequency of sound will reach a maximum sound & then dissipates later. So maximum amplitude varies depending on frequency of stimulus
What is the effect of higher frequency stimulus on the distance the wave will travel along basilar membrane?
greater the frequency of stimulus, the shorter the wave will move along the basilar membrane. Thus, only the lowest frequency of sound can travel the full distance of the basilar membrane.
As the waves travel thru the basilar membrane to distances determined by the frequency of the stimulus, what is being stimulated?
there are auditory receptor cells along the basilar membrane that are mechanically stimulated by displacement of traveling waves.
What does the tuning curve indicate?
shows relationship btw intensity of sound needed to get a stimulus at a certain frequency.
How does the ear turn mechanical info (auditory receptor cells along the basilar membrane being mechanically stimulated via wave displacements) into sensory electrical information?
-cilia of outer hair cells make contact to tectorial membrane
-if basilar membrane bulges UP, so will the tectorial membrane, which will move hair cells in one direction
-if basilar membrane & tectorial membrane go down, will move hair cells in opposite direction.
Are hair cells along the basilar membrane all the same?
No, the hair cells have different properties responding to different frequencies of stimuli. For instance, hair cells at oval window = stiff & short while hair cells at apex = long, and not stuff.
What is the role of the central auditory system
-interpret discharge patterns of auditory nerve fibers to lead to perception of sound
Each CN 8 fiber terminates within cochlear nuclei by branching to each of the cochlear 3 divisions, which are?
***full range of frequency transduced by cochlear is represented in each of the nuclei.
Is there tonotopy associated with the cochlear nuclei?
Yes, dorsal cochlear nuclei = high frequency while ventral cochlear nuclei = low frequency
From cochlear nuclei, the auditory info will terminate at the auditory cortex aka heschel's gyrus. Explain how this cortex is organized.
From 1-D spatial representation w/in cochlea to 3-D spatial representation in auditory cortex. The auditory cortex has a high to low frequency tonotopy. Neurons of similar frequencies are arrayed in a strip that runs perpendicular to tonotopy axis. It is organized from cortical surface to the white matter in COLUMNS.
Based on expts on cats, is the auditory cortex more involved in analyzing pitch patterns or pitch itself?
Auditory cortex is MORE involved w/ analysis of pitch patterns than pitch itself.
Patients with lesions of auditory cortex may have impaired ability to understand speech, but it's not b/c they're deaf. What does this imply?
That the auditory cortex is involved in analyzing pitch patterns more so than just pitch itself. The patient can hear but b/c of lesions in auditory cortex, the patient has impaired ability to analyze the patterns of pitch, leading to impaired ability to understand speech.
In order to increase the decibel measurement of a sound, one would have to alter its wave
Are cochlear implants designed to induce electromechanical pressure waves within the cochlear fluid?