L16 Acoustic and Vestibular System Flashcards
What is sound?
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
What is the division of the auditory system
Peripheral Auditory System - outer, middle and inner ear
Central Auditory System - Pathways and auditory cortex
What does the periphery auditory system consist of
Outer ear
Middle ear
Inner earF
Function of Periphery auditory system
receive and process all sounds, extends from the auricle to the cochlea
Outer Ear
Auricle
external auditory canal
Function of the auricle
- 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)
What is the middle ear made of
ear drum
3 ossicles
Eustachian tube
Three ossicles
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)
Eardrum (middle ear)
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
Eustachian Tube (middle ear)
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
»_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
»_space; increase and pressure, pain, hearing difficulties
Inner ear made of
Cochlea
Organ of Corti
Function of inner ear
- convert mechanical signals from the middle ear into electrical signals.
- to maintain balance by detecting position and motion (vestibular system)
Cochlea (Inner ear)
shaped as a spiral
* inside the cochlea is the cochlear duct.
* duct contains a fluid called endolymph, as well as the organ of Corti.
Organ of Corti (Inner ear).
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.
Pathway of Organ of Corti
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.
How does the brain know the intensity of the sound (strong/weak)?
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)
»_space; greater frequency of pulses of hair cells
(closer pulses)
weak sound:
»_space; small bend of the hair cells (stereocilia)
»_space; smaller frequency of pulses of hair cells
How does the brain know the frequency of the sound?(low /high pitch)
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”
Explain Auditory Pathway
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Location of Auditory cortex
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
Function of the Auditory Cortex
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.
Central Auditory Processing Disorder
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
Conduction Deafness
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.
Nerve Deafness Causes
Causes:
* Diseases of the cochlea
* Damage of cochlear nerve
* Defects in the central auditory pathway
Presbycusis (Nerve Deafness)
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
Acoustic Neuroma (schwannoma)
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)
Tuning Fork Test
Used to distinguish between conduction deafness and nerve deafness
Weber Test :
Rinne Test:
Hyperacusis
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
Function of the Vestibulocochlear Nerve
Transits sound and equilibrium from inner ear to brain
This nerve arises between the medulla and pons
Where does the vestibulocochlear nerve enter the brain
Internal Auditory Meatus
Where does the vestibulocochlear nerve divide
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
peripheral Vestibular System
Consist of:
* vestibular labyrinth (inner ear: semicircular canals, urticle, saccule)
* vestibular ganglion
* vestibulochochlear nerve (CN
VIII)
Vestibular Labyrinth
three fluid-filled loops = semi-circular canals: sense head movement
(rotational movement)
utricle and saccule: sense head position (linear acceleration)
Linear Acceleration
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
How does gravity impact linear acceleration
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
Rotational Movement of the Head
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
»_space; movements of the endolymphatic fluid
Process of Head Movement
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
Describe the Vestibular Pathway
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Benign Paocysmal Positional Vertigo
Common form of vertigo
Symptoms of Benign paroxysmal positional vertigo (BPPV)
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
Cause of BPPV
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
Treatment of BPPV
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
