Hearing Flashcards
how are sound waves produced?
periodic variation in air pressure
what is the speed of sound?
343m/s
767mi/h
how is sound characterized?
by its frequency and intensity
what determines pitch?
frequency
how is frequency measured?
cycles per second or Hertz (Hz)
what is the audible range of frequencies for humans?
20Hz - 20k Hz
what is the frequency of ultrasound and what can it be heard by?
> 20k Hz
dogs, cats, mice, dolphins, etc
what is the frequency of infrasound and what can it be heard by?
<20Hz
elephants, whales
what are low frequency sounds implicated in?
car sickness
what determines loudness?
intensity
how is intensity measured?
decibels (dB)
what is the loudest tolerable sound?
120dB
what are the 3 functional divisions of the ear?
- external ear
- middle ear
- inner ear
what is the external ear composed of?
- pinna (auricle or tragus)
- external acoustic meatus (auditory canal)
what is the pinna?
cartilaginous sound capturing convoluted funnel of the external ear
what is the external acoustic meatus?
2.5cm long tunnel of the external ear that ends at the eardrum
the middle ear is an ____ chamber composed of…
air-filled
1. tympanic membrane
2. ossicles
3. tensor tympani & stapedius mm
what is the tympanic membrane?
9mm diameter conical membrane of the middle ear
name the 3 ossicles
malleus
incus
stapes
the inner ear (labyrinth) is a ____ filled membrane composed of…
fluid-filled
1. cochlea
2. vestibule
3. semicircular canals
what is the cochlea?
(auditory system)
tube of the inner ear that is spiraling 2.5x around the conical bony modiolus
sound waves cause displacement of the ____ membrane which is transmitted to the ____
tympanic
ossicles
the convex portion of the tympanic membrane extends into the cavity of the ____ ear and is attached to the ____
middle
malleus
how are the malleus, incus and stapes held together?
tiny synovial joints
how is tympanic membrane displacement transferred to the inner ear?
stape’s footplate pistons in & out onto the oval window
the middle ear cavity connects to the nasopharynx via the ____, and to the mastoid air space (antrum) via the ____
Eustachian tube (auditory tube)
aditus
tensor tympani is innervated by ____ and attaches to the ____, while the stapedius is innervated by ____ and attaches to ____
V - malleus
VII stapes
function of tensor tympani & stapedius mm
attenuation reflex:
make ossicles more rigid in order to dampen very loud sounds (decreases by 10dB)
why doesn’t the attenuation reflex protect from sudden loud sounds?
has a 50-150ms delay
what is the function of the middle ear?
enhance pressure so that signal is not lost in translation from air (external & middle ear) to fluid (inner ear)
if the middle ear did not function, what would happen to the energy from sound?
only 2% of energy would be transferred from external to inner ear as compared to 67% that normally does
how does the middle ear amplify pressure?
- surface area of oval window is 17x smaller than tympanic membrane
- ossicles act as levers to increase force output on oval window
what are the 2 membrane covered holes at the base of the cochlea?
oval window
round window
what happens when the oval window is displaced by stapes?
- causes fluid movement, most of which is absorbed by fluid in cochlea
- any “unabsorbed” energy distorts the round window
what are the 3 fluid filled chambers of the cochlea?
- scala vestibuli
- scala media
- scala tympani
what are the 2 membranes between the fluid filled chambers of the cochlea and where are they located?
scala vestibuli
- Reissner’s membrane
scala media
- basilar membrane
scala tympani
scalas vestibuli and tympani contain ____ and connect at the…
perilymph (Na rich)
helicotrema at apex of cochlea
scala media (cochlear duct) contains ____
endolymph (K rich)
how does stria vascularis distribute ions in the endolymph?
secreting K while absorbing Na against their concentration gradients
(endolymph has ^K)
the Organ of Corti is located on the ____, and is covered by the ____
basilar membrane
tectorial membrane
what is the Organ of Corti?
auditory sensory receptor
describe the structure of the basilar membrane
base = narrow + rigid
apex = wide + floppy
the base of the basilar membrane codes ____ frequency sounds, while the apex codes ____ frequency sounds
high
low
(tonotopic map)
the Organ of Corti is composed of…
- inner & outer hair cells
- rods of Corti (pillar cells)
- supporting cells
what ultimately produces a receptor potential on a hair cell?
bending of stereocilia on hair cell (converts mechanical energy to receptor potential)
describe the location & stereocilia of inner hair cells
- arranged in a row between pillar cells & bony modiolus
- stereocilia extend in endolymph inferior to tectorial membrane
describe the location & stereocilia of outer hair cells
- arranged in 3-4 rows distal to pillar cells
- stereocilia extend in endolymph ending in tectorial membrane
hair cells synapse with dendrites of ____ located in the _____
bipolar spiral ganglion cells
modiolus
what causes the bending of stereocilia ?
when basilar membrane is affected by scalas’ fluid movement, all other structures in Organ of Corti move up or down, causing stereocilia to bend sideways
upward movement of the basilar membrane causes…
- stereocilia bend so that K channels on tips open and depolarize hair cells
- causes Ca channels to open
- release of NT
- synapse between hair cells & dendrites of spiral ganglion cells
downward movement of the basilar membrane causes ____
hyperpolarization
most spiral ganglion cells receive synapses from ____
inner hair cells
why are outer hair cells implicated with sound amplification in the inner ear?
ototoxic antibiotics selectively destroy them
axons of the spiral ganglion cells form the ____ n
cochlear
the cochlear nerve follows the ____ organization of the basilar membrane so that…
tonotopic
each fiber is most responsive at a specific frequency
the cochlear nerve travels to the ____ to synapse with the ____
medulla
cochlear nuclei
how many ventral and dorsal cochlear nuclei are there?
2 ventral
1 dorsal
name and describe the cell types of the ventral cochlear nuclei
- stellate cells: encode variety of frequencies
- bushy cells: fire at onset of sound & aid in localization of sound in horizontal axis
name and describe the cell types of the dorsal cochlear nucleus
- fusiform cells: excited or inhibited by wide variety of frequencies & aid in sound localization in vertical axis
- tuberculoventral cells: respond with a delay & inhibit echo interference
cochlear nuclei synapse bilaterally with the ____
superior olivary nuclei
where do fibers of the cochlear nuclei cross?
trapezoid body
function of medial superior olivary nucleus
sound localization in horizontal axis by processing info about auditory time delay between the 2 ears
when is interaural time delay most striking?
low frequencies
function of lateral superior olivary nucleus
sound localization by processing intensity difference between the 2 ears
when are intensity interaural differences most striking?
high frequencies
what forms the lateral lemniscus?
fibers from the superior olivary nucleus
some fibers from the lateral lemniscus will synapse with the ____, but most synapse with the ____
nucleus of the lateral lemniscus
inferior colliculus
describe the nuclei of the inferior colliculus and their functions
- 4 layered dorsal nucleus: gathers auditory & somatosensory info
- multilayered central nucleus has a complete tonotopic map
the medial geniculate nucleus receives input from the ____ via the ____
inferior colliculus
inferior brachium
the medial geniculate nucleus holds a complete ____ map
somatotopic
fibers from the medial geniculate nucleus form the ____ and end in the ____
auditory radiation
primary auditory cortex
transverse temporal gyri of heschl constitute areas ____ and ____ of Brodmann and are located…
41 & 42
near superior temporal gyrus
transverse temporal gyri are ____ organized
tonotopically
function of transverse temporal gyri of heschl
2nd point of sound localization: columns that are responsive to every audible frequency and interaural relationship
conductive hearing loss results from…
insult to middle ear
- otitis media (middle ear infection): may cause scar tissue that hinders movement of tympanic membrane or ossicles
- otosclerosis (no known cause): ossification between ossicles
sensorineural hearing loss results from…
loss of cochlear hair cells
Weber’s Test
- place tuning fork on vertex or nasion (midline of skull)
- sound lateralizes to the ear with conductive deafness or away from the ear with sensorineural deafness
Rinne’s Test
- place tuning fork on mastoid process
- when pt can no longer hear it, place tuning fork near ear and patient should be able to hear it
- if not = conductive hearing loss
