What is tonotopy?
Distance along basilar membrane travelled by wave is dependent on its frequency
What are cochlear implants used for?
To restore some hearing to people who have lost cochlear hair cell function but sensory neurones of spiral ganglion are still functional
How do cochlear implants work?
- Processor breaks sound into frequency components
- Diff frequency channels transmitted to implant receiver
- Signal conducted along wires that end in electrodes in cochlea
- Electrodes stimulate nerve cells underneath appropriate region of basilar membrane
High sound frequencies activate electrodes at base of cochlea, low frequencies at apex
Where is the superior olivary nucleus?
Medulla
Where is the medial geniculate nucleus?
Thalamus
Where is the primary auditory cortex?
- Heschl’s gyrus
- Superior medial surface of temporal lobe
- Has tonotopic map of frequency
Where are Wernicke’s and Broca’s area?
- Secondary auditory cortex
- Left hemisphere
- Involved in lang. processing
What is Wernicke’s aphasia?
- Lang fluent + grammatical but often meaningless
- Nonsense words
What is Broca’s aphasia?
- Language halting + non-grammatical
- Lack of pronouns, articles, conjunctions…
What is the role os the stapedius muscle?
Limits movement of stapes to protect cochlea from loud noise
What nerve supplies the stapedius muscle?
Facial nerve
What happens in Bells palsy?
= Facial nerve pasly
Increased sensitivity to noise = hyperacusis
What is tinnitus?
Virtual sound - ringing/buzzing sensation
Originates within brain
What causes tinnitus?
- Ear wax build up, ear infections, glue ear, osteosclerosis
- Hair cell damage from high intensity noise exposure or drug side effects
- Lesions of auditory nerve
What is pulsable tinnnitus?
Real sounds from blood flow in ear, muscle activity or grinding of jaw joint
What are the mechanisms for noise induced hearing loss?
- Metabolic overactivity = increased free radical production from mitochondria
- May be associated with excessive increase in IC [Ca]
- Blood supply may not provide sufficient nutrients = apoptosis
- Mammalian hair cells can’t regenerate
At what level does noise-induced hearing loss first occur?
Reduced sensitivity at 4kHz
What happens when the ear is exposed to damaging noise levels?
- First sign = disruption of hairs on hair cell
- Longer exposure to intense sound = rounding up + shortening of hairs
- Final stages = remaining parts of hairs fuse into single mass
