Auditory Flashcards
define audition
sense of hearing
describe general functions of audition
Mechanisms within the ear and brain that translate sound in our environment into meaningful neural signals
define sound
audible variations in air pressure
how is sound created?
molecules are displaced forward leaving a corresponding area of pressure
How do sound waves vary in two ways?
they either run in amplitude or frequency
define amplitude
intensity; peak to trough;
perceived as differences in loudness
define frequency
# of compressions per second pitch
name the 3 main divisions of the ear
Outer
Middle
Inner
What does the outer ear contain?
Pinna Auditory canal (external auditory meatus)
define Pinna
Funnel shaped outer ear made of skin and cartilage
what does the Pinna actually do?
the funnel shape of the pinna helps collect sound waves and direct them toward the external auditory meatus
define auditory canal
channel leading from the pinna to the tympanic membrane
what is the auditory canal lined with?
hairs and ceruminous glands
what do the ceruminous glands produce?
cerumen
define cerumen
its a modified sebum (earwax) which helps prevent foreign objects from reaching the tympanic membrane
what is the main function of the auditory canal?
it opens into pharynx and equalizes air pressure between outside ear and middle ear cavity
what does the middle ear consist of?
tympanic membrane
ossicles
the middle ear is a ______ chamber
air-filled
the tympanic membrane can also be called…
the eardrum
the tympanic membrane is ______ and _____ shape
semitransparent
oval
the tympanic membrane moves in response to what?
variations in air pressure
name the three layers of the tympanic membrane
simple cuboidal epithelium on the inner surface
a thin stratified squamous epithelium on the outer surface
a layer of CT between them
what is does the tympanic membrane separate?
the external ear from the middle ear
define ossicles
a series of bones in a small air filled chamber
what is the main function of the ossicles?
to transfer the movement of the tympanic membrane into the movement of a second membrane covering a hole in the bone of the skull
name this hole
oval window
name the bones of the middle ear
Malleus
Incus
Stapes
the stapes sits on top of what?
the oval window
more force is required to displace ___ than air
fluid
so then what do the bones do?
they amplify the pressure
what is displaced in response to the movement of the tympanic membrane?
malleus
what does this lead to?
the top of the incus is pushed towards the outer ear and pushes the bottom towards the inner ear
what happens next?
the stapes is consequently pushed forward against the oval window which is compressed inward
the eustachian tube connects what?
the air-filled middle ear to the mouth
the inner ear is ____ filled.
fluid
what happens in the inner ear?
this is where physical movement of the oval window is converted into neural signal.
where does this “conversion” exactly take place?
cochlea
the cochlea also contains this structure which is not part of the auditory system but is involved in balance.
vestibular apparatus and the semicircular canals
what does the cochlea do?
is transduces the mechanical displacement of the oval window into a neural signal
name the main components of the cochlea
scala vestibuli scala tympani scala media organ of corti basilar membrane fluid
the organ of corti contains…
auditory receptor cells
where is the organ of corti located?
in the scala media
what does the basilar membrane do?
it separates scala media and scala tympani
fluid is continuous between what?
scala vestibuli and scala tympani
the organ of corti contains this membrane
tectorial membrane
the tectorial membrane has…
both thick and thin sides
what can be found under the tectorial membrane?
stereocilia
what are the 2 types of hair cells found under the tectorial membrane?
outer hair cells
inner hair cells
mechanical force pushes on…
the oval window
fluid within the cochlea is _______
incompressible
so this means…
the fluid is pushed forward
how does this conserve the wave properties of the sound
the movement of the fluid has frequency and amplitude
what does this cause?
causes the round window to bulge out
structures within the cochlea are….
not rigid
_______________ is flexible and bends inn response to sound
basilar membrane
the basilar membrane is ___ at apex than base
wider
stiffness of the membrane decreases from…
base to apex
this resembles a what?
a diving board
what doe high frequency sounds have?
higher energy and can displace the stiffer part of the basilar membrane (near base)
lower frequency sounds have..
lower energy and displace the apex end
____ responds to high frequency and the ___ responds to low frequency
base
apex
basilar membrane establishes a place code in which…
different locations are maximally deformed in response to different frequency sounds
name the structures found in the organ of corti
outer hair cell inner hair cell tectorial membrane reticular membrane basilar membrane stereocilia spiral ganglion
of all those structures, which are involved as auditory receptors?
hair cells
stereocilia
what is a critical event in the transduction of sound into neural signal
bending of these cilia
what does the hair do?
it extends above the reticular membrane and come in contact with the tectorial membrane
what happens when the basilar membrane moves in response to the motion of the stapes?
the whole complex moves as a unit either towards or away from the tectorial membrane and the lateral motion of the reticular membrane bends the sterocilia
if the hair gives a downward phase, what happens?
hyperpolarization (closed channel)
if the hair gives an upward phase, what happens?
depolarization (opened channel and K+ can enter)
changes in cell potential result in what?
the opening of K+ channels on the tips of the stereocilia
the response of the depolarization is…
Ca++ channel is activated
what does this influx of Ca++ lead to?
causes the release of synaptic vesicles from the end of the hair cell
describe the sequence of the displacement of basilar membrane.
- physical displacement of the basilar membrane bends the stereocilia
- bending of the cilia either opens or closes a K+ channel
- When K+ enters, the hair cell depolarizes
- Depolarization activates a Ca++ channel
- Ca++ influx causes NT release
where do the action potentials occur at?
the level of the output ganglion
multiple outer hair cells make…
synaptic contact with a single ganglion cell
what does the ganglion do next?
it makes a synaptic contact with a single inner hair cell
what is the most abundant hair cell?
the outer hair cell
what do these outer hair cells do?
it alters the stiffness of the tectorial membrane
there are two cochlea, each projecting to its…
cochlear nucleus
within the cochlear nucleus this process branches…
dorsal cochlear nucleus
posterior ventral cochlear nucleus
anterior ventral nucleus
what do the dorsal and posterior ventral cochlear nuclei do?
they send efferent projections to the contralateral inferior colliculus
how does it do this?
via the nucleus of the lateral leminiscus
what does the anterior ventral cochlear nucleus permit?
the detection of interaural time differences
the medial superior olive (MSO) has cells that…
receive coincident innervation from the right and left anteroventral cochlear nucleus
the length of the axonal connections determine…
which MSO cell receives coincident activation by action potential
the anteroventral cochlear nucleus projects directly…
to the ipsilateral lateral superior olive (LSO)
the anteroventral cochlear nucleus projects indirectly to the…
contralateral lateral superior olive
how does this occur?
via the inhibitory neuron originating in the medial nucleus of the trapezoid body
the anteroventral cochlear nuclear firing rate is greater for sound when…
the sound has higher intensity
when do LSO firing be the highest on that side?
when the sound arises directly lateral on the same side to the listener
____________ from the ipsilateral anteroventral cochlear nucleus will be maximal
excitation
__________ from the contralateral MNTB will be minimal
inhibition
where does the dorsal and posteroventral cochlear nuclei send projections?
to the inferior colliculus
the highly processed auditory information is then relayed to the…
medial geniculate nucleus of the thalamus
from the thalamus, this information ascends to the…
primary auditory cortex
where is the primary auditory cortex located?
in the temporal lobe
frequency is a consequence of what?
the mechanics of the basilar membrane
name the steps of basic auditory pathway
- sound waves move tympanic membrane
- tympanic membrane moves ossicles
- ossicles move membrane at the oval window
- motion at the oval window moves fluid in the cochlea
- movement of the fluid in the cochlea causes a response in sensory neurons
- signal is transferred and processed by a series of nuclei in the brain stem
- information is sent to a relay in the thalamus
- MGN projects to the primary auditory cortex in the temporal lobe
