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
LOOK AT PAGE
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
