Ch. 53 Hearing Flashcards
Conduction of sound pathway
tympanic membrane –>ossicles–>chochlea
tympanic membrane is attached to the
handle of the malleus
3 bones in middle ear:
- malleus
- incus
- stapes (connects to oval window –>inner ear)
Attenuation of sound:
after 40-80 seconds of intense sound:
1. stapedius uscle
2. tensor tympani mucles
are contracted with increased rigitidy in ossicles = reduces sound conduction
Attenuation of sound benefits (3)
- protect cohlea from damaging vibration
- masks low frequency sounds in environments
- decreases hearing sensitivity to own speech
Transmissin of sound through bone
Cochlea implanted in temporal bone. Vibration enter skull = fluid vibrations in chochlea
Cochlea is made of:
3 tubes coiled side by side:
1. scala vestibuli
2. scala media
3. scala tympani
Sound vibration pathway
vibrations–>scala vestibuli via faceplate at oval window –>faceplate moves inward to push fluid forward and outward to move fluid backward
Stiff, short fibers are near
oval window
stiff, short fibers beat at
very high frequency
long, limber fibers are near
tip of cochlea
long, limber fibers vibrate best at
low frequency
Fluid wave travels along
basilar membrane
fluid wave is strongest at
point of natural resonant frequency
at this point, membrane can vibrate back and forth with ease
fluid waves travel ____ initially then get _____
fast initally, then get progressively slower as it goes into chochlea
this allows high frequecy sounds to spread out and separate from one another
Pattern of sound wave
A - stapes is all the way in
B - Neutral
C - stapes all the way out
______ frequency waves are closest to stapes
higher
organ of corti role
generates nerve impulses in response to vibration of basilar membrane
Excitation of organ of Corti
- Stereocillia project upward from hair cells, which are embedded in gel coating of tectorial membrae
- bending of hairs in one direction depolarizes hair cells, bending in another direction hyperpolarizes them
- inward and outward movement of basialr fiber causes hairs to shear back and forth in tectorial membrane
____% of info comes from inner hair cells of organ of Corti
90-95%
what opens or closes mechanically gated ion channels in hair cells?
bending of sterocilia
pivoting of steriocillia
opens or closes mechanically gated ion channels
What is the electircle potential of hair cells at tips of sterocilia
+80
(creates extra sensitivity)
place principle
determining sound frequencies by poition along basilar membrane
How does loudness occur
as sound becomes louder, amplitude of vibration in basilar membrane and hair cells increases –>more hair cells become stimulated (spatial summation)
decibel unit
10-fold increase in sound energy = 1 decibel
logarithm of actual intensities
frequency of sound (age comparison)
young: 20-20,000 cycles per second
older: 50-8,000 cycles per second
young has broader range
Nerve fibers from spiral ganglion of Corti enter
dorsal and ventral cochlear nuclei in upper part of medulla–>2nd order neurons to opposite side of brain stem–>terminate in superior olivary nucleus
From superior olivary nucleus, auditory pathway
passes upward through lateral lemniscus where some fibers terminate and other –>colliculus where they synase
colliculus synapses to
medial geniculate nucleus –>synapse to auditory cortex
auditory synapse location
superior gyrus of temporal lobe
fibers pass through reticular activating system of brain stem, which:
activates nervous system in response to loud sounds
signals form both ears transmitted through the pathway of
both sides of the brain
Primary auditory cortex directly excited by
projections from medial geniculate body
Secondary association areas are excited secondarily by
impulses from primary auditory cortex
Sounds frequency perception
high frequency sounds excite nuerons at one side of tonotopic map, low frequency excite on other side
What “sharpens” frequency
lateral inhibition
Auditory cortex is important for
discrimination of tonal and sequential sound patterns
destruction of both primary auditory cortices would result in
reduced hearing
damage to only one primary auditory cortices results in
slightly reduced hearing and affects ability to localize sound
Lesions affecting auditory association area:
interfere with ability to interpret meaning of sound
How is direction of sound determined
time lag between entry of sound in one ear and entry into opposite ear
=
difference between intensities of the sounds in two ears
What determines if sound is front or behind, above of below?
Pinnae - changes quality of sound based on direction
Lateral superior olivary nucleus role
detecting direction from which sound is coming
medial superior olivary nucleus role
detects time lag between acoustic signals entering two ears
sounds from different areas around the head stimulate
different olivary neurons
Deafness can be caused by impairment of(3)
- Cochlea
- auditory nerve
- CNS circuits from ear
Main cause of deafness
impairment of physical structures of the ear that conduct sound to cochlea
Permanent deafness MOA:
damage to cochlea or auditory nerve
Method for measuring hearing
audiometer - emits tone with ranging frequencies
