Auditory Pathways Flashcards
What does frequency affect
The distance along the basilar membrane travelled by the wave
Where do high frequency sounds finish on the basiliar membrane
At a peak near the base
Where do low frequency sounds finish on the basilar membrane
At a peak near the apex
What does tonopy mean
The brain is able to distinguish a cord with lots of notes as they have distinctive peaks which the brain then has to be able to distinguish somewhere
What are cochlear implants used for
To restore some hearing
Who can cochlear implants be used in
People who have lost cochlear hair cell function, but in whom the sensory neurones of the spinal ganglion are still functional. Hair cells are damaged but the apical cells underneath are still intact
How do cochlear implants work
- A processor breaks down sound into its frequency components. 2. The different frequency channels are transmitted to the implant receiver. 3. The signal is conducted along wires that end up in electrodes in the cochlea. 4. The electrodes stimulate the nerve cells underneath the appropriate region of the basilar membrane
Where is the tonopic relationship of frequencies to position seen
Not only on the basilar membrane but at all levels within the auditory pathways- it is the principle on which cochlear implants work
What need to happen to axons when travelling to the brain
They need to be kept in order
What do axons descend in
Tracts called lateral lemniscus
What happens at the superior olivary nucleus in the medulla
There is an exchange of information from the left and right side of the brain which provides spatial sound awareness and judgment made on time and intensity of sound- stereophonics
What happens in the inferior colliculi in the midbrain
Controls visual and auditory reflexes e.g. hear a bang and turn to look where it came from. The reflex in the midbrain happens fast to rotate muscles in the neck, this occurs via the tip-toe spinal tract. The optic part of the brain occurs in the same part of the midbrain result in the reflex of turning to look at something that you see in your peripheral vision
What happens in the medial geniculate nucleus in the thalamus
Important in communication and control of information going to the cortex
Where is the primary auditory cortex
(Heschl’s gyrus) is tucked into the superior-medial surface of the temporal lobe. It has a tonotopic map of frequency
What do the auditory components of the brain do
Analyse pitch and language
What do the motor aspects of the brain do
Analyse rhythm
What areas are involved in language processing
Wernicke’s and Broca’s area
Describe Wernicke’s aphasia
Language fluent and grammatical but often meaningless including some nonsense words that sound similar to real ones
Describe Broca’s aphasia
Language halting and non-grammatical (lack of pronouns, articles, conjunctions)
What is Wernicke’s area important in
Decoding language when it is coming in
What is Broca’s area important in
In the motor cortex and is involved in fluency and linking words. Contains neurones with auditory roots
What is occupational deafness
Hearing loss due to industrial noise
What is the role of the stapedius muscle
Limits the movement of the stapes to protect the cochlea from loud noise
What is the stapedius muscle supplied by
The facial nerve (CN VII)
What may Bell’s palsy (facial nerve palsy) result in
Increased sensitivity to noise, hyperacusis
What is the stapedius muscle activated by
Loud sound
Why do our own voices when recorded sound different
Sound has been transmitted through air. . Before we start to speak, the stapedius muscle activates so that low frequency sound from our own voice (transmitted via soft tissue and bone) is attenuated
What is noise legislation
You are only allowed to expose someone to 87dB for an 8 hour shift for 5 days a week.
What happens to safe exposure time with each 3dB increase
It halves 9-dB is 4 hour limit, 105dB is a 7 minute limit, 120dB is 12 second limit
Describe noise-induced hearing loss
Ttemporary changes in hearing sensitivity after exposure to loud music- temporary deafness may be experienced after exposure to high intensity sound e.g. after a period of time at a rock concert, or in a loud industrial environment
What are the symptoms of noise induced hearing loss
Ear discomfort after exposure, sounds appear muffled, difficulty in interpreting speech particularly if there is a background noise, ringing or buzzing sensation in the ears
Describe tinnitus
. A symptom not a specific condition - may be described as a ringing, whistling or buzzing. This sensation is virtual (not real) sound and originates within the brain
What are possible causes of tinnitus
Conditions that reduce the perception of external sounds e.g. ear wax build up, ear infections, glue ear, otosclerosis. Hair cell damage due to high intensity noise exposure, or drug side effects (e.g. aspirin, quinine, antibiotics). Lesions of the auditory nerve e.g. acoustic neuroma (benign tumour)
What is pulsatile tinnitus
Real sounds from blood flow in the ear, muscle activity or grinding of the temporo-mandiblar (jaw) joint
Describe the treatment of tinnitus
Masking (using white noise or music), Tinnitus Retraining Therapy (helping the patient to habituation to, and therefore ignore, the tinnitus)
What effects whether drugs have an ototoxic effect
Depends on the genetic background of the patient
What are NSAIDs toxic to and what effect may this have
NSAIDs are toxic to hair cells therefore may affect hearing and balance.
What may be toxic to hair cells
NSAIDs. Amniglycoside antibiotics, antineoplastics
Describe the mechanisms of temporary and permanent threshold shifts
a. Metabolic overactivity leading to an increase in free radical production from mitochondria. b. Blood supply may be associated with an excessive increase in intracellular calcium. c. Blood supply may not provide sufficient nutrients.
d. Apoptosis may result- mammalian hair cells do not regenerate. e. An older hypothesis that hair cells are physically damaged is losing ground
What does noise induced hearing loss typically first appear as
A reduction in sensitivity at about 4Hz- speech becomes harder to interpret because consonants produce sound in this band
Why is the 4Hz band lost
Because it is close to the resonance frequency of the external auditory canal so that it is transmitted most efficiently to the eardrum
