L16 Acoustic and Vestibular System

Question 1

What is sound?

Answer 1

Sound is a pressure variation, caused by a vibrating object (vocal cords), that propegates in an elastic medium (air)

Sound wave is captured by the peripheral auditory system

Question 2

What is the division of the auditory system

Answer 2

Peripheral Auditory System - outer, middle and inner ear

Central Auditory System - Pathways and auditory cortex

Question 3

What does the periphery auditory system consist of

Answer 3

Outer ear
Middle ear
Inner earF

Question 4

Function of Periphery auditory system

Answer 4

receive and process all sounds, extends from the auricle to the cochlea

Question 5

Outer Ear

Answer 5

Auricle
external auditory canal

Question 6

Function of the auricle

Answer 6

• act as a funnel and captures the sounds of the environment
• shape helps locate the source of the sounds
• amplifies the sounds of human speech
• protective function (cerumen (ear wax) and the hairs of the external auditory canal
  make collect dust, bacteria)

Question 7

What is the middle ear made of

Answer 7

ear drum
3 ossicles
Eustachian tube

Question 8

Three ossicles

Answer 8

three ossicles = bones of the middle ear:
* Malleus: handle is embedded in the membrane of the eardrum
* Incus
* Stapes: attached to the oval window = membrane-covered opening of
the inner ear)

Question 9

Eardrum (middle ear)

Answer 9

Membrane

• in the presence of pressure variations in
  the air (sound), the eardrum vibrates
• induces a movement of the malleus,
  incus, stapes
• air pressure variations (sounds) are
  transformed into a sequence of
  movements

Question 10

Eustachian Tube (middle ear)

Answer 10

provides the middle ear with air and ensures that the pressure in the tympanic cavity is similar to the one in the external auditory canal
&raquo_space; equalize air pressure between the atmosphere
and the middle ear important in allowing drainage of fluid and secretions from the middle ear and thereby preventing middle ear infections (otitis media)

blockage: leads to accumulation of fluid in the middle ear space
&raquo_space; increase and pressure, pain, hearing difficulties

Question 11

Inner ear made of

Answer 11

Cochlea
Organ of Corti

Question 12

Function of inner ear

Answer 12

• convert mechanical signals from the middle ear into electrical signals.
• to maintain balance by detecting position and motion (vestibular system)

Question 13

Cochlea (Inner ear)

Answer 13

shaped as a spiral
* inside the cochlea is the cochlear duct.
* duct contains a fluid called endolymph, as well as the organ of Corti.

Question 14

Organ of Corti (Inner ear).

Answer 14

contains the sensory cells that allow us to hear
* these cells are called hair cells, because
they have small hairs = stereocilia
* there are two types of hair cells:
inner hair cells (IHC)
outer hair cells (OHC)
* inner hair cells are the actual sensory
receptors
* outer hair cells serve to amplify to
movement of the basilar membrane and
increase its resolution.

Question 15

Pathway of Organ of Corti

Answer 15

sound

eardrum vibrates

movement of the malleus, incus, stapes

stapes makes a piston movement

movement of the endolymph in the cochlear
duct

this movement causes the displacement of the membranes surrounding the cochlear duct and, in turn, the stereocilia are bent.

the hair cells then send an electrical
impulse, which is transferred from the
cochlear nerve to the brain.

Question 16

How does the brain know the intensity of the sound (strong/weak)?

Answer 16

Peripheral auditory system:
sound intensity is encoded by the frequency
of the pulses emitted by the hair cells.

strong sound:
» extensive bend of the hair cells(stereocilia)
&raquo_space; greater frequency of pulses of hair cells
(closer pulses)

weak sound:
&raquo_space; small bend of the hair cells (stereocilia)
&raquo_space; smaller frequency of pulses of hair cells

Question 17

How does the brain know the frequency of the sound?(low /high pitch)

Answer 17

the message sent to the brain depends on the
place of the cochlea that enters in vibration:

high-pitched sounds activate the base of the
cochlea

low-pitched sounds activate the top of the
cochlea.

this organization is called “tonotopy”

Question 18

Explain Auditory Pathway

Answer 18

LOOK AT PAGE

Question 19

Location of Auditory cortex

Answer 19

primary auditory cortex (A1) is located in
the superior temporal gyrus, right under
the lateral fissure.

primary auditory cortex is organized
tonotopically

> > posterior part responsive to high tones
anterior part responsive to low tones

Question 20

Function of the Auditory Cortex

Answer 20

analysis of sound characteristics
(frequency, duration, location,
intensity), initiated in the brainstem,
continues in the auditory cortex.

the auditory cortex integrate all
perceived sound information and form
a coherent “whole”: the auditory
scene.

Question 21

Central Auditory Processing Disorder

Answer 21

Caused: dysfunction in the auditory cortex

Symptoms:
patients have difficulty processing the
characteristics of sounds, although they are not deaf (i.e., their ear and peripheral auditory system are intact)

problems to follow conversations when there are multiple speakers, due to difficulty in determining the localization of sounds

> > have a negative impact on communication

Question 22

Conduction Deafness

Answer 22

caused by interruption of the passage of sound waves through the external or middle ear

Causes:
* Obstruction by wax (cerumen) or a foreign
body in the external auditory meatus
* Otosclerosis: abnormal formation of bone
within the middle ear, resulting in fixation of the stapes.

> > most frequent cause of progressive
conduction deafness.

• Otitis media: inflammation of the middle ear.

Question 23

Nerve Deafness Causes

Answer 23

Causes:
* Diseases of the cochlea
* Damage of cochlear nerve
* Defects in the central auditory pathway

Question 24

Presbycusis (Nerve Deafness)

Answer 24

Presbycusis
age related hearing loss (progressive, irreversible) affects both ears

Cause:
degenerative disease of the organ of corti:
loss of receptor hair cells at the basal aspect of the cochlea resulting in characteristic high
frequency hearing loss.

Treatment:
Hearing aids

Question 25

Acoustic Neuroma (schwannoma)

Answer 25

consists of a peripheral nerve tumor of the
vestibulocochlear nerve (CN VIII).

located in the internal auditory meatus or in the cerebellopontine angle of the posterior cranial fossa.

symptoms: unilateral deafness and tinnitus (ear ringing)

Question 26

Tuning Fork Test

Answer 26

Used to distinguish between conduction deafness and nerve deafness

Weber Test :

Rinne Test:

Question 27

Hyperacusis

Answer 27

disorder in loudness perception patients suffering from hyperacusis may appear overly sensitive to a range of sounds, finding many noises unbearable and painfully loud.

Causes:
* changes in hearing due to aging
* one-off exposure to loud noise, such as an explosion
* a slap on the ear
* chronic exposure to noise, such as working in a noisy environment
* head injury
* surgery to the ear
* Neurodevelopmental disorders (Autism)

Treatment:
hearing protection, sound therapy, cognitive behavioural therapy

Question 28

Function of the Vestibulocochlear Nerve

Answer 28

Transits sound and equilibrium from inner ear to brain

This nerve arises between the medulla and pons

Question 29

Where does the vestibulocochlear nerve enter the brain

Answer 29

Internal Auditory Meatus

Question 30

Where does the vestibulocochlear nerve divide

Answer 30

inside the temporal bone, at the distal end of the internal acoustic meatus, the vestibulocochlear nerve divides to form:

• cochlear nerve = conveys sound information
• vestibular nerve = conveys information about balance = equilibrium

Question 31

peripheral Vestibular System

Answer 31

Consist of:
* vestibular labyrinth (inner ear: semicircular canals, urticle, saccule)
* vestibular ganglion
* vestibulochochlear nerve (CN
VIII)

Question 32

Vestibular Labyrinth

Answer 32

three fluid-filled loops = semi-circular canals: sense head movement
(rotational movement)

utricle and saccule: sense head position (linear acceleration)

Question 33

Linear Acceleration

Answer 33

Utricle and saccule are both made of macula tissue (composed of hair cells)

Stereocilia hair cells extend into a gel known as the otolith

This contains calcium carbonate crystal, making it dense

Question 34

How does gravity impact linear acceleration

Answer 34

Gravity will cause the otolith to move seperately from macula in response to head movements

The exact tilt of the head is interpreted by the brain as the pattern of hair- cell depolarisation

Question 35

Rotational Movement of the Head

Answer 35

semicircular canals: are three ring-like extensions of the vestibule.
there are three semi-circular canals:

anterior: oriented in vertical plane
posterior: oriented in vertical plane
lateral: oriented in horizontal plane

each of the three semicircular canals has at its base a bulbous expansion called the ampulla

the ampulla contains the hair cells that respond to rotational movement
&raquo_space; movements of the endolymphatic fluid

Question 36

Process of Head Movement

Answer 36

head rotation: causes the fluid in the semicircular canal to move, but with a lag
which produces a deflection of the cupula in the direction opposite to the head
rotation which in turn causes the hair cells to depolarize.

semicircular canals contain several ampullae, with some oriented horizontally
and others oriented vertically

Question 37

Describe the Vestibular Pathway

Answer 37

Look at page

Question 38

Benign Paocysmal Positional Vertigo

Answer 38

Common form of vertigo

Question 39

Symptoms of Benign paroxysmal positional vertigo (BPPV)

Answer 39

Symptoms: appear suddenly, and in episodes of short duration
* Dizziness
* A sense that you or your surroundings are spinning or moving
(vertigo)
* A loss of balance or unsteadiness
* Nausea
* Vomiting

Question 40

Cause of BPPV

Answer 40

Cause:
within the labyrinth of the inner ear collections of calcium crystals = otoliths

otoliths become dislodged from their usual
position within the utricle

migrate into one of the three semi-circular
canals causes abnormal endolymph fluid
displacement and a resultant sensation of vertigo

Diagnosis:
Dix-hallpike test

Question 41

Treatment of BPPV

Answer 41

Reposition maneuvers:
* Semont maneuver
* Canalith repositioning procedure (CRP)

none of these maneuvers addresses the presence of the particles = otoconia, rather it changes their location.

aim to move these particles from some locations in the inner ear that cause symptoms such as vertigo and reposition them to where they do not cause these
problems

acute (anti-vertigo medication)
surgery