auditory system Flashcards
What is the range of human hearing
20Hz-20KhZ
Key components of the auditory system
- ) Outer ear
- ) Middle ear
- ) Inner ear
- ) Central auditory pathways
Outer ear structure: what is the pinna
It is a cartilaginous structure
What is the pinna formed from
Formed from pharyngeal arches 1 & 2 (6x Hillocks of His)
When is the pinna formed in gestation
Formed between 10th and 18th week in utero
What is the function of the pinna
It directs soundwaves towards ear canal
What is the ear canal made up of
1/3 cartilage and 2/3 bone
What is the middle ear made of
Bones/muscles/tubes
What are the bones (ossicles) of the middle ear
Malleus/Incus/Stapes
What are the muscles of the middle ear
Tensor tympani and stapedius
What are the tubes of the middle ear
Eustachian tube
What are the size of the bones
- ) Malleus: 23mg
- ) Incus: 27mg
- ) Stapes: 2.5mg
What is the role of the middle ear
- Acoustic impedance match between air and fluid-filled inner ear
- Amplification of the airborne sound vibration
What takes place when energy transfers energy from outer ear to inner ear?
- There is a 200 fold increase boost in pressure from TM to inner ear
- This is the ossicular chain
What is the role of muscles in the middle ear?
- Protects the inner ear from acoustic trauma
- Stiffens the ossicular chain
- Stapedius stimulated acoustically
- Tensor tympani is for voluntary and involuntary control and chewing
What is the role of the eustachian tube
- ) Ventilation of the middle ear space
2. ) Drainage of secretions
Key facts about the cochlea
- ) It has 2 openings: round and oval window
- ) A fluid filled bony tube
- ) 3 compartments: scala tympani/scala media/scala vestibuli
- ) Has two ionic fluids
What are the ionic fluids in the cochlear
- ) Endolympth: high K+
2. ) Perilympth: Na+ rich
How are gradients maintained
- ) Na+ & K+ ATPase pump
- ) NKCCI and CIC-K chlorine channels
- If you have ion channel abnormalities: get deafness
Cochlear components: the basilar membrane features
- ) Narrow at base
- ) Wide at apex
- ) Stiff at base
- ) Floppy at base
- ) High frequencies detected at base
- ) Low frequencies at apex
What happens when the basilar membrane
Causes movements of specialised mechanical transducing cells
What are the two types of hair cells
- ) Inner hair cells: mechanical transduction
2. ) Outer hair cells: fine tuning
Inner ear: how it goes from waves to sparks
- ) Sterocilia moves and a rapid response is required
2. ) Mechanically gates K+ channels open which causese depolarisation
Inner ear: how it goes from waves to sparks
- ) Sterocilia moves and a rapid response is required
- ) Mechanically gates K+ channels open which causes depolarisation
- ) The depolarisation will result in voltage gated Ca2+ channels being opened
- ) Releases neurotransmitter: Glutamate
- ) Repolarisation through K+ efflux (Into K+ poor perilympth)
Tonopothy and the role of the outer hair cells
- each nerve responds maximally at a specific frequency
- outer hair cells can alter the stiffness of the basilar membrane to ensure max stimulation at one site and dampened response at another
- increase resolution
How is sound information encoded?
- encoded in formation for neural transmission
- Frequency (pitch): encoded in nerves by location along the basilar membrane
- Intensity (loudness): enoded in nerves by numbers responding and by firing rate
- Sound transduction: inner hair cells
- Amplification: outer hair cells
How do the signals travel from neuron to brain
- ) Auditory fibres: spiral ganglion
- ) Spiral ganglion to cochlear nerve (VIII)
- ) Central auditory pathway
What are MSO neurons
They are coincident detectors. They respond only when excitatory signals arrive simultaneously
- Anatomical differences in conncectivity allow each MSO neuron to be sensitive to sound source from location
What is the central auditory pathway
Eight nerve-> cochlear nucleus-> olive-> lateral leminiscus-> inferior colliculus
Types of hearing loss
- ) Conductive hearing loss
2. ) Sensorineural hearing loss
Conductive hearing loss
Defective outer/middle ear
Sensorineural hearing loss
Defective inner ear
