auditory system Flashcards
1
Q
what is sound
A
the displacement of air particles following a sinusoidal pattern of compression and rarefaction
2
Q
what does amplitude refer to
A
loudness of sound
3
Q
what do low pitched sounds mean
A
repeat less frequently than high pitched sounds
4
Q
what is the range of human hearing
A
20Hz-20,000Hz
it changes during life
5
Q
at what frequency is the ear most sensitive
A
at 1000 - 4000Hz
6
Q
components of auditory system
A
outer ear - is just movement of air
middle ear - is just movement of air
inner ear - is now movement of fluid
central auditory pathways
7
Q
what does outer ear do
A
helps you collect sound
8
Q
what is the outer ear formed from
A
pinna - cartilaginous structyre
formed from pharyngeal arches 1 and 2
forms between 10th and 18th week in utero
ear canal
9
Q
role of pinna
A
directs sound waves toward ear canal
picks out high pitched sounds more than low pitched
10
Q
describe ear canal
A
1/3 cartilage and 2/3 bone
11
Q
what does middle ear contain
A
bones
muscles
tubes
12
Q
what does middle ear do
A
is for the transmission of sound
13
Q
which bones in middle ear
A
malleus
incus
stapes
14
Q
which muscles in middle ear
A
tensor tympani
stapedius
15
Q
what tube in middle ear
A
eustschian tube
16
Q
what does the middle ear house
A
the ossicular chain
17
Q
what does inner ear do
A
is for the conversion of sound into neural impulses
18
Q
what is the role of the middle ear
A
acoustic impedance match
between air and fluid filled inner ear
19
Q
how much energy loss from air to fluid
A
97%
20
Q
how does the middle ear reduce energy loss
A
it does amplification of the airborne sound vibration = makes it louder
so middle ear is sound amplifier
this increases energy by 200 fold
21
Q
roles of muscles in the middle ear
A
protection of inner ear from acoustic trauma
stiffens the ossicular chain
22
Q
stimulation of stapedius
A
stapedius stimulated acoustically
reflex arc : 3 or 4 neurones
6-7ms reaction time in cats
25ms in man
23
Q
role of tensor tympani
A
voluntary and involuntary control
chewing
24
Q
what is the the role of the eustachian tube
A
ventilation of the middle ear space
drainage of secretions
25
what is inner ear
a set of fluid filled sacs, encased in bone
26
what is cochlea responsible for
hearing
27
what is labyrinth responsible for
balance
28
in elevation of inner ear
vestibulochlear. erie
29
structure of cochlea
2.5 turns fluid filled bony tube
2 openings - round window and oval window
3 components (scala tympani, scala media & scala vestibuli)
2 ionic fluids
30
where does sound first enter the ear
through the pinna (or auricle) which is the exterior part of the ear
It then enters the ear via the external auditory canal/meatus
31
what does the shape of both the pinna (or auricle) & external auditory canal/meatus help with
helps to amplify and direct the sound
32
what happens to sound after entering the external ear
it makes its way through the canal, to the tympanic membrane
(eardrum)
as the air molecules push against the membrane, it causes the tympanic
membrane to vibrate at the same frequency as the sound wave
the membrane vibrates slowly to low frequency sounds and very rapidly to
high frequency sounds
33
what does the tympanic membrane mark
the end of the external ear and the start of the middle ear
34
what provides sensation to the middle ear
the glossopharyngeal nerve CNIX
35
what is pressure like in the external auditory canal/meatus and middle ear cavity
normally equal to atmospheric pressure
36
how is the middle ear exposed to atmospheric pressure
via the eustachian tube (or
auditory tube) which connects the middle ear to the pharynx
37
how does the eustachian tube open into the pharynx
through a slit-like opening which is
normally closed, EXCEPT when muscle movements result in the opening of
the tube during swallowing, yawning or sneezing
38
what causes a difference in pressure between the middle and external ear
changes in altitude
39
what happens to the middle ear when the pressure outside the ear and in the external auditory meatus change
the middle ear initially remains constant due to the fact that the eustachian tube is closed
this constant pressure can stretch the tympanic membrane resulting in pain -
which can be relieved by yawning/swallowing which in turn results in the opening of the eustachian tube thereby allowing the pressure in the middle ear to equilibrate with the external atmospheric pressure
40
what happens to the vibrations of the tympanic membrane
they are transmitted to the inner ear (for processing) through a moveable chain of three bones - the ossicles (the smallest bones in the body)
41
what are the ossicles
1. malleus
2. incus
3. stapes
(MIS)
vibrations to the inner ear are transmitted through these bones in this order
42
what is there between ossicles
synovial joints
43
what do synovial joints between ossicles do
act as a piston and couple the vibrations of the tympanic membrane to the OVAL WINDOW (a membrane covered opening between the middle and inner ear)
44
what happens to the total force of a sound wave applied to the tympanic membrane
it is completely transferred to the oval window
However, due to the fact that the oval window is much smaller than the tympanic membrane, the force per area is much greater which is required to adequately transmit the sound energy through the FLUID FILLED COCHLEA
45
how can the amount of energy transmitted to the inner ear be lessened
by the contraction of two small muscles in the middle ear - the tensor tympani
& stapedius
46
what innervates tensor tympani
V3 (mandibular branch trigeminal)
47
what innervates stapedius
CN7 (facial)
48
what does tensor tympani attach to
the malleus
49
what does contraction of tensor tympani do
dampens the bones movement - innervated by the mandibular division (V3) of the TRIGEMINAL NERVE CN5
50
what does the stapedius attach to
the stapes
51
what do tensor tympani and stapedius do as a reflex
they act reflexively to CONTINUOUS LOUD NOISE to protect the
delicate receptor apparatus in the inner ear
52
can tensor tympani and stapedius protect the inner ear from SUDDEN INTERMITTENT LOUND SOUNDS
no
53
what is the inner ear called
the cochlea (the organ of hearing)
54
describe cochlea
a spiral-shaped (coiled around 2.5 - 2.75 times), fluid filled space in the temporal bone
55
what is the cochlear duct
a membraneous tube that completely divides the cochlea lengthwise
56
what does the cochlear duct contain
the sensory receptors of the auditory
system
57
what is the cochlear duct filled with
a fluid called endolymph - a compartment of extracellular fluid containing a high concentration of K+ and a low concentration of Na+ (this arrangement of concentrations is normally seen in intracellular fluid)
On either side of the cochlear duct are compartments filled with perilymph, which is similar in composition to
cerebrospinal fluid (CSF)
58
where is the scala vestibuli
above the cochlear duct
begins at the oval window
it forms the entrance to the inner ear
from the oval window
59
where is the scala tympani
below the cochlear duct and
connects to the middle ear
via a second-membrane covered opening, the round window
60
where are the scala vestibuli and scala tympani continuous
at the far end of the cochlear duct
at the helicotrema
61
what movement creates waves of
pressure in the scala vestibuli
1. sounds waves from the external acoustic meatus cause the tympanic membrane to move in and out which in turn is transmitted to the ossicles
which in turn transmit this
movement to the oval window
2. this results in the oval window
moving in and out of the scala
vestibule
62
where are the waves of pressure from the scala vestibuli transmitted to
the majority are transmitted across the cochlear duct with some being transmitted toward the helicotrema and into the scala tympani where the pressure is relieved by the movements of the membrane of the round
window
63
what does the basilar membrane form
the side of the cochlear duct closest to
the scala tympani
64
what does the organ of corti contain
the ears sensitive receptor cells,
- pressure difference across the duct causes the basilar membrane to vibrate
65
describe the base of the basilar membrane
narrow & stiff and thus sensitive to high
frequencies
66
describe the apex of the basilar membrane
wider & less stiff and thus is sensitive to
low frequencies
67
what are hair cells
the receptor cells of the
organ of corti
are mechanoreceptors that have hairlike stereo-cilia protruding
from one end
68
what can damage the stereocilia of the hair cells
some antibiotics
69
how many anatomically separate groups of hair cells are there an what are they
2
inner hair cells
outer hair cells
70
how many rows of inner hair cells are there
a single row
71
how many rows of outer hair cells are there
4-5 rows
72
describe the stereocilia of inner hair cells
extend into the endolymph fluid and
convert pressure waves caused by the movement of fluid in the cochlear duct
into receptor potentials
73
describe the stereocilia of outer hair cells
are embedded in the overlying
tectorial membrane and mechanically alter its movement to sharpen frequency tuning at each point along the basilar membrane
74
what causes bending of the stereocilia
- the tectorial membrane overlies the
organ of corti
- as the pressure waves displace the basilar membrane
- the hair cells move in relation to the
stationary tectorial membrane
- causing bending of the stereocilia
75
what happens when the stereocilia bend towards the tallest member of the bundle
- fibrous connections called TIP LINKS pull open mechanically gated K+ channels,
- resulting in an influx of K+ from the
surrounding endolymph (K+ rich)
thereby depolarising the membranes
- this change in voltage triggers the
opening of voltage-gated Ca2+
channels near the base of the cell,
- which in turn triggers neurotransmitter release (since Ca2+ causing neurotransmitter containing vesicles to migrate to the presynaptic membrane)
76
what happens when hair cells bend away from the tallest member of the bundle
- slackens the tip links
- thereby closing the channels and
allowing the cell to rapidly repolarize
- hair cells release glutamate
- which in turn binds to and activates protein binding sites on the terminals of the afferent neurones
77
what results in the generation of action potentials in neurones
as sound waves vibrate the basilar membrane, the stereocilia are bent back and forth, the membrane potential of the hair cells rapidly oscillates and bursts of glutamate are released onto afferent neurones
the axons join to form the COCHLEAR BRANCH of the VESTIBULOCOCHLEAR NERVE (CN VIII)
78
what does greater energy of the sound wave (loudness) mean
the greater the energy (loudness) of the sound wave, the greater the
frequency of action potentials generated in the afferent nerve fibres
79
why does each hair cell respond to a
limited range of sound frequencies
due to its position on the basilar membrane
one particular frequency will stimulate it most strongly
