Chapter 16 – The abnormal auditory system
Noise induced hearing loss
- Inner ear - Hair cells and stereocilia convert hydrodynamic forces within cochlea into
neural impulses in auditory nerve
o Damage to these affect transduction process and hair cells are most vulnerable
to overstimulation (high levels)
o Low levels can lead to outer hair cell stereocilia swelling or fusing
o Severe damage won’t repair
organ of corti mechanical destruction, exceeding it’s elasticity causes
permenant loss of hair cells
o Mild damage can repair hearing to normal
May be due to physicochemical processes associated with metabolic
activity
- Middle ear – high levels can rupture tympanic membrane
Hearing loss due to noise exposure
- Change in threshold/sensitivity
- Noise induced threshold shift – increase in threshold
- Temporary threshold shift – if it returns to preexposure level
o Typically reaches a limit known as asymptotic threshold shift
o Factors in stimulus exposure affect amount of TTS e.g level, duration,
temporal pattern.
Generally, more TTS is produced at higher frequencies
Relationship between hearing loss and temporal pattern is complex but
intermittent exposure may aid recovery somewhat
- Permanent threshold shift – doesn’t return to preexposure level
- Compound threshold shift – combination of TTS and PTS
- Recovery of hearing after noise exposure
o Threshold shift builds up as duration of exposure increase then decreases after
cessation
Ototoxic drugs
- Chemicals poisonous to tissue of auditory system
- Several can lead to tinnitus
o Subjective, high frequency ‘ringing’ and sometimes the loudness can debilitate
individuals
o Can sometimes be accompanied by hearing loss e.g salicylate (in aspirin) in
large quantities can lead to T and HL, why those with arthritis can experience
them as they tend to have large aspirin doses
Aging
- HL due to aging = presbycusis
- Can start in 20s but isn’t noticeable till 50+
- The more noise exposure they’ve experienced, the greater the loss
Noise induced hearing loss
- Inner ear - Hair cells and stereocilia convert hydrodynamic forces within cochlea into
neural impulses in auditory nerve
o Damage to these affect transduction process and hair cells are most vulnerable
to overstimulation (high levels)
o Low levels can lead to outer hair cell stereocilia swelling or fusing
o Severe damage won’t repair
organ of corti mechanical destruction, exceeding it’s elasticity causes
permenant loss of hair cells
o Mild damage can repair hearing to normal
May be due to physicochemical processes associated with metabolic
activity
- Middle ear – high levels can rupture tympanic membrane
Hearing loss due to noise exposure
- Change in threshold/sensitivity
- Noise induced threshold shift – increase in threshold
- Temporary threshold shift – if it returns to preexposure level
o Typically reaches a limit known as asymptotic threshold shift
o Factors in stimulus exposure affect amount of TTS e.g level, duration,
temporal pattern.
Generally, more TTS is produced at higher frequencies
Relationship between hearing loss and temporal pattern is complex but
intermittent exposure may aid recovery somewhat
- Permanent threshold shift – doesn’t return to preexposure level
- Compound threshold shift – combination of TTS and PTS
- Recovery of hearing after noise exposure
o Threshold shift builds up as duration of exposure increase then decreases after
cessation
Ototoxic drugs
- Chemicals poisonous to tissue of auditory system
- Several can lead to tinnitus
o Subjective, high frequency ‘ringing’ and sometimes the loudness can debilitate
individuals
o Can sometimes be accompanied by hearing loss e.g salicylate (in aspirin) in
large quantities can lead to T and HL, why those with arthritis can experience
them as they tend to have large aspirin doses
Aging
- HL due to aging = presbycusis
- Can start in 20s but isn’t noticeable till 50+
- The more noise exposure they’ve experienced, the greater the loss
