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Auditory System Flashcards

1
Q

What is hearing range and what is most sensitive

A

20 to 20,000Hz

1000-4000Hz

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2
Q

Function of Outer ear

A

collect sound

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3
Q

Function of Middle ear

A

transmission of sound

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4
Q

Function of inner ear

A

conversion of sound into neural impulses

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5
Q

1) where does sound enter

A

First enters the ear via the pinna (or auricle) which is the exterior part of the ear

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6
Q

2) what happens after sound enters the ear via the pinna (or auricle)

A

then enters the ear via the external auditory canal/meatus

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7
Q

3) what happens after the sound enters the ear via the external auditory canal/meatus

A

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

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8
Q

4) what happens to sound after the tympanic membrane vibrates

A

The vibrations are transmitted to the inner ear (for processing) through a moveable chain of three bones - the OSSICLES (smallest bones in the body )

Firstly through the MALLEUS
then the INCUS then STAPES

(MIS)

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9
Q

Tympanic membrane slow vibrations=

Tympanic membrane fast vibration =

A

low freq sounds

high frequency sound

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10
Q

Whys is the shape of both the pinna and external auditory canal/Meatus important

A

Help to amplify and direct the sound

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11
Q

What marks the end of external ear and beginning of middle

A

tympanic membrane

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12
Q

What cranial nerve provides sensation to middle ear

A

Glossopharyngeal CNIX

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13
Q

What is the middle ear

A

an air filled cavity in the temporal bone of the skull

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14
Q

What are the pressures in the external auditory canal/meatus and middle ear cavity

A

normally equal to atmospheric

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15
Q

How is middle ear exposed to atmospheric pressure

A

via Eustachian tube (or auditory tube) which connects middle ear to pharynx

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16
Q

How does the eustachian tube open into pharynx

A

through a slit-like opening which is normally closed, EXCept when muscle movements result in the opening of the tube e.g. during swallowing, yawing or sneezing

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17
Q

What can changes in altitude do to ear

A

Cause difference in pressure between middle ear and external ear

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18
Q

When the pressure outside the ear and in the external auditory meatus change what happens to the middle ear initially then what

A

middle ear initially remains constant due to the fact that the Eustachian tube is closed

This constant pressure can stretch the tympanic membrane = pain which can be relieved by yawning/swallowing with in turn results in the opening of the eustachian tube = allowing the pressure in the middle ear to equilibrate with the external atmospheric pressure

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19
Q

What joints do the ossicles have in-between them

A

synovial joints

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20
Q

5) what happens after the ossicles transmit the sound into the inner ear

A

They 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)

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21
Q

Whats the oval window

A

a membrane covered opening between the middle and inner ear

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22
Q

6) the total force of a sound wave applied to the tympanic membrane is completely transferred to the oval window

but the oval window is much smaller than the tympanic membrane. What does this mean?

A

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

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23
Q

How can the amount of energy transmitted into the inner ear be lessoned?

A

By the contraction of two small muscles in middle ear

TENSOR TYMPANI (V3 mandibular branch of trigeminal)

STAPEDIUS (CNVII facial)

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24
Q

What does the tensor tympani attach to and whats its function

A

Attaches to the MALLEUS and its contraction dampens the bones movement

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25
what innervates the tensor tympani
MANDIBULAR DIVISION (V3) OF THE TRIGEMINAL (CNV)
26
What does the stapedius attach to and how does it control sound
Attaches to the stapes and also dampens the sound
27
What innervates the stapedius
FACIAL NERVE CN VII
28
what do the tensor tympani and the stapedius do
Act reflexively to CONTINUOUS loud noise to protect the delicate receptor apparatus in the inner ear thes muscles cannot protect the ear from SUDDEN intermittent out sounds
29
What is the inner ear
called the COCHLEA (organ of hearing)
30
What is the cochlea
Spiral shaped (coiled around 2.5-2.75 times) fluid filled space in the temporal bone
31
How is the cochlea divided and what does this contain
almost divided completely lengthwise by a membranous tube called the cochlea duct - which contains the sensory receptors of the auditory system
32
What does the cochlea duct contain
filled with a fluid called ENDOLYMPH - a compartment if extracellular fluid containing a high conc of K+ and low conc of Na+ (this arrangement of concs is normally seen in intracellular fluid)
33
On the other side of the cochlear duct what is there
Compartments filled with PERILYMPH | similar composition to CSF
34
Where is the SCALA VESTIBULI
Above the cochlear duct and begin at the oval window remember since vestibule is like an entrance so it from the entrance to the inner ear from the oval window
35
Where is the SCALA TYMPANI
Below the cochlear duct and connects to the middle ear via a second membrane covered opening - the ROUND WINDOW
36
The scala vestibuli and tympani are continuous ate the far end of the cochlear duct the..
helicotrema look at pic
37
1a) What do sound waves from the external acoustic meatus cause
cause the tympanic membrane to move in and out which is transmitted to the ossicles which in turn transmit this movement to the oval window
38
2a) tympanic membrane move in and out which is transmitted to the ossicles which in turn transmit this movement to the oval window what happens then
results in the oval window moving in and out of the scala vestibuli this movement causes waves of pressure in the scala vestibuli That majority of these waves of pressure 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
39
Where does the ORGAN OF CORTI sit
The side of the cochlear duct closest to the scala tympani is formed by the basilar membrane, upon which sits the organ of court
40
What does the organ of corti contain
ears sensitive receptor cells, pressure difference across the duct causes basilar membrane to vibrate
41
what part of the basilar is sensitive to which frequencies
The base of basilar membrane is narrow and stiff = sensitive to HIGH frequencies The Apex of the basilar membrane is wider and less stiff = sensitive to low frequencies
42
Receptor cells of the organ of corti are called
Hair cells
43
What are the hair cells in the organ of corti
They are mechanoreceptors that have hair like STEREO-CILIA protruding from one end
44
What can some antibiotics damage in the organ of corti
can damage the stereocilai of the hair cells
45
There are two anatomically separate groups of hair cells;
SINGLE ROW of inner hair cells 4-5 ROWS of outer hair cells
46
How do the stereo cilia of the inner hair cells convert pressure waves
The stereo cilia of the 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
47
How to stereo cilia of outer hair cells work
the stereo cilia 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 look at a pic
48
1b )How is the tectorial membrane involved in sound conversion
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 = bending of the stereo cilia
49
2b) What happens after the stereo cilia bend
when the stereo cilia bend toward the tallest member of the bundle, fibrous connections called TIP LINKS, stretch and pull open mechanically gated K+ channels, = influx of K+ from the surrounding endolymph (K+rich) = depolarising membranes
50
3b) what happens when influx of K+ from the surrounding endolymph (K+rich) depolarises membranes
This change in village triggers the opening of Ca2+ channels near the base of the cell, = influx of Ca2+ = vesicles containing neurotransmitter migrate to presynaptic membrane = triggers neurotranmitter release
51
what happens if you bend the stereo cilia of hair cell in opposite direction
slackens the tip links = closing the K+ channels = cells rapidly repolarises
52
4b) what happens when neurotranmitter releases into cleft
(neurotransmitter released from hair cells is glutamate) Glutamate binds and activates protein-binding sites on the terminals of the afferent neurones.
53
5b) as sound waves vibrate the basilar membrane the stereocila are bent back and forth, the membrane potential of the hair cells rapidly oscillates and bursts of glutamte are released onto afferent neurones. what happens what Glutamate binds and activates protein-binding sites on the terminals of the afferent neurones.
This results in the generation of action potentials in the neurones, the axons of which join to own the COCHLEAR BRANCH of the vestibulocochlear nerve CN VIII
54
A v loud sound means what
The great the loudness = greater the energy of the sound wave, = the greater the frequency of action potentials generated in the afferent nerve fibres
55
How does the position of the hair cell on the basilar membrane mean for the hair cell
Due to its position on the basilar membrane, each hair cell respond to a limited range of sound frequencies, with one particular frequency stimulating most strongly.
56
What is the spiral ganglion
Cochlear nerve fibres make dendritic contact with hair cells of the organ of corti within the cochlear duct the cell bodies of these fibres lie within he cochlea-- are collectively called the spiral ganglion
57
c1 At what level does the cochlear nerve join the brainstem c2 and where does it end c3 then where?
rostral medulla its fibres bifurcate and end in the DORSAL and VENTRAL cochlear nuclei, which lie close to the inferior cerebellar peduncle From cochlear nuclei the second order neurones ascend into the pons where the fibres travel to the superior olivary nucleus
58
c4 Where do fibres from superior olivary nucleus go
fibres travel to the INFERIOR COLLICULUS of the midbrain
59
What other kind of fibres does the superior olivary gland have
superior olivary nucleus has fibres that leaves the brainstem in the vestibulocochlear nerve, and end in the organ of corti, these serve an inhibitory function and adjust transmission of auditory info through the cochlear nerve by mediating contractions of the tensor tympani and stapedius in response to loud noises
60
c5 what happens after fibres travel to the INFERIOR COLLICULUS of the midbrain
from here the inferior brachium (nerve fibre) carries the auditory info to the medial geniculate body of the thalamus
61
c6 what happens after the inferior brachium (nerve fibre) carries the auditory info to the medial geniculate body
from the medial geniculate body, fibres travel through the internal capsule to the primary auditory cortex of the temporal lobe - situated on the dorsal surface of the superior temporal gyrus
62
Where is the primary auditory cortex situated
on the dorsal surface of the superior temporal gyrus
63
whats the region of the temporal lobe surrounding the primary auditory cortex called and what happens here
WERNICKE'S AREA (auditory association cortex) and it is here where auditory info is interpreted and understood
64
Where is wernicke's area located
superior temporal lobe
65
What happens if wernicke's area is damaged
Patient will not be able to understand questions and there speech will be incomprehensible
66
Summary of path of cochlear branch of vestibulocochlear nerve (CN VIII) (5)
1 cochlear nuclei 2 superior olivary nurcleus 3 Inferior colliculus 4 medial geniculate body via inferior brachium 5 Primary auditory cortex in wernicke's area
67
I'MAuditory
Inferior colliculus, Medial geniculate body, for AUDITORY info THEREFORE BY DEFAULT Superior colliculus and lateral geniculate body Must be for vision
68
What is Bell's Palsy
Acute uni lateral inflammation of the facial nerve, results in pain behind the ear (do to the chords tympani and also the facial nerve in the interior auditory meatus), = Paralysis of facial muscles and failure to close eye
69
what is the CHORDA TYMPANI and where does it run
Its a branch of the Facial nerve CN VII | Carries taste messages from the tongue and runs through the middle ear to brain
70
Why is there pain behind the ear in bells palsy
Bc facial nerve CN VII exists cranial cavity into the internal acoustic meatus which is behind the cochlea
71
What is the vestibular apparatus and what does it consist of
Connected series of Endolymph filled, membranous tubes that also connect with the cochlear duct. Also have hair cells 3 membranous semicircular canals and 2 saclike swellings; UTRICLE & SACCULE all of which lie in the temporal bone on either side of the head
72
what do the hair cells in the vestibular apparatus do?
detect changes in motion and position of the head by a stereo cilia transaction mechanism
73
What do the semicircular canals detect and how are they activated?
Detect angular acceleration during rotation of the head alone three perpendicular axes - activated when nodding the head up and down, shaking he head from side to side and tipping the head so that the ear touches the shoulder.
74
What are the receptor cells of the semicircular canals like?
contain stereo cilia like the receptor cells of the organ of corti These stereo cilia are encapsulated within a gelatinous mass, the CAPULA which extends across the lumen of each semicircular at the ampulla (a slight bulge in the wall of each duct)
75
Whenever the head moves the semicircular canal within its bony enclosure and the attached bodies of the hair cells all move with it but endolymph filled duct ..
is not attached to the skull and due to inertia, remains in its original position = the moving ampulla is pushed against the stationary fluid which in turn causes bending of the stereo cilia and the alteration in the rate of glutamate release from hair cells ... glutamate crosses synapse and activates neurones associated with the hair cells, initiating the propagation of action potential towards the brain
76
How does speed and magnitude of rotational movements determine the direction in which the stereo cilia are bent and which hair cells are stimulated
Glutamate is released from hair cells at rest and the release increases and decreases from resting rate according to the direction in which hairs are bent
77
Each hair cell receptor has how many directions of maximum neurotransmitter release?
Each hair cell receptor has one direction of maximum neurotransmitter release so when the stereo cilia are bent in this direction the receptor cell depolarises when the stereo cilia are bent in the opposite direction the cell hyper polarises
78
How are hair cells only stimulated during acceleration or declaration
When the head continuously rotates at a steady velocity the duct fluid begins to move at the same rate as the rest of the head and the stereo cilia slowly return to resting position
79
What is NYSTAGMUS and what causes it
rapid jerky back and forth movement of the eyes damage to canals of one side slow phase towards the damaged side and rapid reset away from damaged side
80
What can pouring ice cold water into the external auditory meatus cause
NYSTAGMUS bc causes convection currents in semicircular canals
81
What are the otolothic organs
utricle and saccule
82
What do the otolithic organs do
Provide info about linear acceleration of the head and about changes in head position in relation to gravity
83
when do the hair cells in the utricle respond
Point nearly straight up when standing respond when head is tipped away from horizontal plane or to linear accelerations in the horizontal plane
84
When do the hair cells in the saccule respond
They project at right angles to those of the utricle respond when you move from lying to standing position or to vertical accelerations like those produced when jumping on trampoline
85
what are Otoliths
Tiny stones (tiny calcium carbonate crystals) embedded in the gelatinous substance which covers the stereocilia projecting from the hair cells in the utricle and saccule they make the gelatinous substance heavier than the surrounding endolymph
86
function of gelatinous otolithic material
In response to a change in position the gelatinous otolithic material moves in response to forces of gravity and pulls again the hair cells = stereocilia on the hair cells bend and the receptor cells are stimulated and the action potential is propagated via the vestibular nerve (branch of the vestibulocochlear nerve CNVIII)
87
3 uses of vestibular info
1 CONTROL OF EYE MOVEMENTS so that in spite of changes to head position the eyes can remain fixed the same point nystagmus can occur as a result of unusual vestibular inout in health people 2 REFLEX Mechanisms of maintaining upright posture &balance Vestibular apparatus plays a role in support of the head during movement and orientation of the head in space 3 PROPRIOCEPTION conscious awareness of the position & acceleration of the body, perception of space surrounding the body and memory spatial info
88
Where do the central processes of vestibular fibres end
mostly end in the vestibular nuclei of rostral medulla

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