The auditory system Flashcards
Tell me about the scale of hearing loss?
- 1:6 projected to reach 1:5
- 11 million people with hearing loss in the UK (900,000 with severs or profound loss) 2035 15.6 million
What are the aspirations for hearing loss?
What does this rely on?
Aspiration – preservation or maintenance of hearing across the lifecourse
This preservation relies on adequate function of the complete auditory system – implants also require adequate residual function.
What are hearing aids used for ?
Hearing aids – amplify, CIs – replace IHC function – no pharmacological intervention- mechanistic understanding needed
What is sound characterised by?
Sound is characterised by its pitch (tone) and intensity (loudness)
What are the two characteristics to sound?
Amplitude = loudness/volume
Frequency = Pitch/tone (human hearing range 20Hz – 20kHz, bats 20-200kHz)
Sound (or noises) scale in dB
whats considered good/ bad for hearing?
The human ear structure
Whats the role of the outer and middle ear?
- outer and middle: transmit sound to the inner ear, also help compensate for the loss in sound energy that naturally occurs when the sound waves pass from air into water by amplifying the sound energy during the process of sound transmission
- middle: The primary function of the middle ear is to offset the decrease in acoustic energy that would occur if the low impedance ear canal air directly contacted the high-impedance cochlear fluid
Whats the role of the inner ear?
inner: two jobs, changes sound waves to electrical waves (nerve impulses). Allows the brain to hear and understand sounds. Also important for balance
What are the 3 tiny bones in the middle ear called, and what is their function?
3 bones in middle ear called Ossicles. They transmit sounds from the air to the fluid filled cochlea
What are specialised sensory cells in the inner ear called?
Specialized sensory cells – hair cells - are located within the inner ear
What are the key nuclei of the auditory pathway and what is their role?
The cochlea nuclei
- Cochlea and hair cells role in hearing
- Every step involves processing of the particular sound signal
- Cochlea has an aqueous environment
When sound waves move from the air, tell me about the resistance?
The sound wave is moving from air, which has a low impedance (low resistance) to an aqueous environment in the inner ear which has a high impedance (high resistance)
Tell me about the cochlea amplifier and how it works?
- Cochlea amplifier is a positive feedback mechanism
- Causes the tip links of the OHC hair bundle to open allowing inflow of Na+ and K+ which depolarizes the OHC
- A lengthening of prestin lengthens the hair cell while prestin concentration leads to a decrease in OHC length
The cochlea structure
(has been unrolled in order for structure to be seen more clearly)
Tell me about the fluid filled cavities in the cochlea and what they are filled with?
- Fluid filled cannels running beside each other but filled with different fluid e.g., perilymph and endolymph
- In healthy ear the endolymph has a higher potassium level
- Basal end of cells bathed in perilymph
- Endocochlea potential created from balance between potassium levels
What are the layers of the hair cells
Where are Stereocilia found?
around the inner and outer hair cells
Tell me about the inner and outer hair cells
- Stereocilia are around the inner and outer hair cells
- Outer hair cells sit in little clusters or trios whereas the inner cells are the sensing cells and sit individually
- Inner cells sense the vibrations of sound and help you hear
How are action potentials induced in the sensorys in the hair cells?
Tell me about the basilar membrane of the hair cell?
- Basilar membrane: tapered structure – narrow at one end and gets progressively wider along its length (at base of cochlea at the bottom of the curl)
- Move towards top moves towards the low frequency end of the spectrum that we can perceive
- Topographical mapping of frequency allows us to distinguish between different frequencies/pitches
- Spectral analysis- distinguish between different frequencies
How does this vibrational energy in the basilar membrane get transduced into an electrical signal?
- The mechanical movement of specialized (mechanotransduction)
- sensory cells: hair cells
- stereocilia is deflected to right from its central position as sound wave passes
What in the hair cell structure is important for sound production?
- small Tip link proteins connect…
- outer hair cells involved in amplification process of the cell and control part of movement of membrane. Part of sound management system
Tell me about the tip link protein and what a mutation in this protein can cause
- mutation in tip link can make someone congenitally deaf- very important proteins
- tip links, when flexsion happens the mechanically gated channels open
Tell me aboutt he distortion open channels…
- respond to movement of potassium
- tip links move apart, depolarisation as a result activated
- relayed to cochlea nucleus
- interpreted into a sound
Ionic bases of mechanotransduction
What are the two types of hair cells?
2 types of hair cells (inner – outer)
- Inner = sensory receptors (transduction)
- oHC contract and expand in response to
The electrical currents (active process) in the outer hair cells (OHC)
- Electromotility
- Depolarisation = Contraction
- Hyperpolarisation = Relaxation
Whats the function of the outer hair cells?
Amplifies motion of basilar membrane enhances the responsiveness of inner hair cells
Whats the role of cochlea amplifiers?
Cochlear amplifiers: enhances amplitude and sharpness
Tell me how a cochlea implant works?
- The external speech processor captures sound and converts it into digital signals.
- The processor sends the digital signals to an internal receiver-stimulator package.
- The internal implant converts the signals into electrical energy, then sends the energy to an electrode array inside the cochlea.
- Electrodes stimulate the auditory nerve, bypassing damaged hair cells. User perceives the signals as sound.
What type of cochlea implants can you get and what age group tend to get what and why?
- there bilateral and unilateral
- Adults only given one implant because surgery is expensive and traumatic and have cost implications, some adults do have 2, evidence is, is that benefit the person gets between 1 and 2 implants isn’t enough to give someone 2 implants as there’s only a small difference
Bilateral implants
What is hearing loss described as?
Reduced ability to perceive sound (not hear sound) is hearing loss
Summary of the auditory system and hearing
- Describe the gross anatomy of the auditory system
- The specialized sensor is the HAIR CELL
- Describe how mechanical activation of the tip links opens K+ channels which depolarize the hair cell and trigger neurotransmitter release (Transduction)
- Specific movements of the stereocilia and the activation of different populations of hair cells can create different patterns of electrical activity and signaling (Encoding)
- Appreciate the differing roles of the auditory pathway nuclei (Processing)
- Consider hearing loss and cochlear implants
Sound processing (anatomy)
dont need to learn this table, just for information
What are some factors that contribute to hearing loss?
Noise is only one factor that contributes to hearing loss. Age can play a part and also other conditions you have e.g., type II diabetes, cardiovascular disease. More health conditions as you age contribute to hearing loss as you age and as people are living longer
