Auditory System Flashcards
What is sound
The displacement of air particles following a sinusoidal pattern of compression and rerefacation
What does a quieter sound wave look like
Shorter amplitude
Longer wave length
What does a loud sound wave look like
Higher amplitude
Shorter wave length
What does a lower pitch sound wave look like
Lower frequency
Longer wave length
What does a higher pitch sound wave look like
Higher frequency
Shorter wave length
What is the range of human hearing
20Hz to 20KhZ
What are the components of the auditory system
Outer ear- air
Middle ear-air
Inner ear- fluid
Central auditory pathways
What makes up the outer ear
Pinna and ear canal
What is the pinna
The pinna is the cartillagenous structure on the outside of the ear
What is the pinna formed of
It is formed of pharyngeal arches 1 and 2
6x hillocks of His
When does the pinna form
Between weeks 10 and 18 weeks in utero
What is the function of the pinna
Directed sound waves towards the ear canal
What is the ear canal made up of
1/3 cartilage (outer 1/3)
2/3 bone
What is the ear drum also known as
Tympanic membrane
What is the top 1/3 of the ear drum called
Pars flaccida
What are the bottom 2/3 of the ear drum called
Pars tensa
What are the bones of the middle ear
Malleus, incus and stapes
What are the muscles of the middle ear
Tensor tympani and the stapedius
What are the tubes in the middle ear
The Eustachian tube
What is the role of the middle ear
Acoustic impedance match between air and fluid filled inner ear
Amplification of the airborne sound vibration which will make it louder
How much energy is lost transferring air to fluid
97% loss of energy
What is the roles of the muscles of the middle ear
Protection of the inner ear from acoustic trauma
Stiffens the osciular chain
Stapedius is stimulated acoustically
Tensor tympani has voluntary and involuntary control- (chewing)
What is the role of the Eustachian tube
Ventilation of the middle ear space
Drainage of secretions
What is the inner ear
A set of fluid sacs
What is part of the inner ear
Cochlear
Labyrinth
How is the inner ear innervated
Vestibulochochlear nerve
What is the cochlear responsible for
Hearing
What is the labyrinth responsible for
Balance
What is the cochlea made up of
2.5 turns fluid filled bony tube
3 compartments
2 ionic fluids
2 openings
What are the 2 openings in the cochlea
Round window and oval window
What are the 3 compartments in the cochlear
Scala tympani
Scala media
Scala vestibuli
What are the 2 cochlear fluids
Endolymph
Perilymph
How are the gradients of the cochlear fluids maintained
Na, K-ATPase and NKCC1 CIC-K chloride channels
What sits on the basilar membrane
The organ of corti
What are the hair cells of the organ of corti attached to
Tectorial membrane
How are the Scala vestibuli and the Scala tympani connected
The helicotrema
What is tonotopy
The basilar membrane responding to different frequency sounds at different points along the membrane
Where on the basilar membrane are high frequency sound heard
The base
Where on the basilar membrane are low frequencies heard
At the apex
How does the organ of corti move
The basilar membrane is a mobile structure which causes the organ of corti to move
What is the role of the inner hair cells on the organ of corti
Mechanical transduction
What is the role of the outer hair cells of the organ of corti
Fine tuning
How are the stereocillia moved
They are moved in a rapid response.
They move when the mechanically gated potassium channels open which causes a wave or rapid depolarisation, this causes calcium ions to enter through voltage gated channels. This results in a release of neurotransmitters. Repolarisation then occurs through the influx of potassium ions into perilymph which is low on potassium
How is frequency encoded
It is encoded in nerves by location along the basilar membrane
How is intensity encoded
Intensity is encoded by numbers responding and by firing rate
How is sound transduction encoded
Inner hairs cells
How is amplification encoded
Outer hair cells
How does sound reach from the ear to the brain to be processed
Via the auditory fibre in the spiral ganglion
The spiral ganglion then transmits it via the cochlear nerve (8th nerve) to the central auditory pathway in the brain
How is sound localised
Sound is localised by the brain stem
What makes up the central auditory pathway
Eighth nerve
Cochlear nucleus
Olive
Lateral leminiscus
Inferior colliculus
