Audio conduction and transduction Flashcards
How does audio waves arrive to the inner ear?
From outside, enter the ear and vibrate the tympanic membrane-the ossicles on the other side match the impedence (measure of reluctance if the system) to reduce loss of energy as air goes into cochlea, then hair cells
What is conductive hearing loss?
Loss of hearing caused by effects before the tympanim-such as fluid accumuation, perforation of tympanum
What is the cochlea and how does it function?
Snail shape organ filled with fluid
What is the basilar membrane of the cochlear? function?
Elastic structure with heterogenous mechanical propertes that vibrate at DIFFERENT parts along its length depending on the different frequency
->breaks down sounds and distribute them around
Receptors along the whole membrane - these are in the hair cells
How do hair cells function in hearing?
Movements of basilar membrane deflects the hair bundles-and the TIP of each (Tip links), ion channels that open when they connect to other hair. (Tip touching next hair relaxes tip link, opening ion channel)–this reduces stiffness of the hair-and ACTIVELY moves in the direction (amplification mechanism)
the bending of the stereocilia is what transforms audio into electical signal
What are the active process to explain how the cochlea can act?
Cochlea cannot be explained by passive mechanical
Active-amplification (by the hair), Frequency tuning (focus on the peak), Compression non linearity (Amplification, but reduced as becomes louder), Spontanous otoacoustic emission (work perfomed by hair cells tp isolate
What iare the two types of hair cells?
Inner hair cells, under the main hairs
Smaller numbers
Outerhair cells origin of amplification and otoacoustic emission-cell body shortens/elongates when voltage changes
How do nerve fibres transmit the signal from the inner ear?
Hair cells synapse with sensory neurons in cochlear ganglion-each ganglion cell responds best to a particular frequency-mapping
What is sensorineural hearing loss?
Hearing loss when the issue is in the cochlea, nerves, hair cells (Loud sounds can cause that, genetic mutations, some Abx, ageing, demyelination of axons
hair cells do not regenerate
what is the best solution to sensorineural hearing loss?
Cochlear implants-elongated could in the cochlea with electroes corresponding to single frequencies
Need about 20 channels to understand speech, but early models have about 4
Where is the first stop of hearing information in the brainstem?
In medulla, posterior tip of the -two chochlear nuclear- ventrocochlear is more low pitch, dorsal higher pitch
Dorsal pitch also locates sound in the vertical sounds–and once again, each cell reacts best at a specific frequency
spectral cues also come from the ear shape
What is the second step-where does hearing go after medulla?
Superior olivary complex (near center of pons)-it compares the bilateral activity of the cochlear nuclei–interaural time difference is computed and corrected (uses a delay map-delay ines)
After that, lateral superior olive detects the difference in intensities-interaural level difference
THE OLIVES are EXCITED IPSILATERALLY (from cochlear nucleus) but inhbited CONTRALATERALLY (carried by fast, large axons, while ipsi is smaller and slower)
Olives also send ipsi and contralateral feedback to the cochlear (efferent fibres to outer hairs)
How can things go wrong in sensorineural hearing loss in the brain?
Demylination, unbalance between inhbitory and excitatory actions
Where does hearing go to after the pons olives - in the midbrain
In the midbrain-inferior Colliculus
All ascending auditory pathways converge here (each side, away from mickey ears)-is formed of discrete nucleus
IC has part in determining where the sound has come from, adding up all the different sounds-and filter OUT the echo (same sounds but took a longer path)
Then to Superior colliculus
Visual and audiotory maps merge-neurons tuned to respons to stimuli with specific sound direction–this “map” is fundamental for reflexes
What is the final destination of auditory information
Primary auditory cortex-top of temporal lobe
central area of the AC and Tonotopically mapped (which frequency, tonality, etc)-important in gaze control and complex tasks
Can be trained, even remodelles (even in adult)
Finally-superior auditory cortex-
