auditory system - obsolete Flashcards
What is the human hearing range?
20Hz - 20kHz
define pitch
perception of frequency
how is sound intensity defined?
amount of energy delivered per second - number of Joules per second passing through one square meter.
How is sound measured.
Decibel scale - logarithmic comparison of intensity as opposed to linear.
What is the sensory receptor of the internal ear?
hair cells.
What is a hair bundle?
cluster of modified microvilli called stereocilia
Define impedance.
the reluctance of a system in receiving energy from a source.
What is the frequency at which impedance of the system is minimal called?
resonant frequency.
What is the role of the ossicles?
match the impedance and reduce the loss in energy as the vibration goes from the air to the cochlea
What is conductive hearing loss?
when the ear is not capable of transmitting the vibration of sound waves onto the cochlea
What can cause conductive hearing loss?
fluid accumulation in children. perforated tympanic membrane. abnormal growth of bone obstructing ear canal. barotrauma.
Diabgram of ear including cochlea.
What is contained within the organ of corti?
basilar + tectorial membranes.
Hair cells.
Supporting cells.
How does the cochlea relay information to the basilar membrane?
Motion of stapes generates difference in pressure between the two liquid-filled chambers of the cochlea –> vibration of basilar membrane
What is the role of the basilar membrane?
frequency analyser.
How does the basillar membrane process vibrations?
elastic structure with heterogenous mechanical properties - vibrates at different positions along its length according to different frequencies.
What is the role of the basilar membrane?
breaks complex sounds down
How is information from the basilar membrane receives?
sensory recptors along its length detect the frequences of vibration - hair cells.
How do hair cells relay information to the brain?
motion of basilar membrane deflects the sterocilia.
This bending towards the tallest stereocilium changes internal cell voltage, producing an electric dignal towards the brain.
mechano-transduction (MT)
What is the role of tip links?
tip links connect sterocilia.
Their stretching as sterocilia bend opens ion channels which generate repsonse currents.
ion channel opening relaxes the tip link, relaxing the hair bundle.
Is hair bundle movement an active or passive process?
active due to capacity to do work.
Compare the sparsity of Inner and outer hair cells.
How do their roles differ?
IHCs - 3500 per human cochlea
OHCs - 110000 per human cochlea.
IHCs - afferent projections (to brain) - relay info.
OHCs - efferent projections (from brain to ear) - cochlear amplification.
How do OHCs aid cochlear amplification?
They stretch and elongate when internal voltage changed - electromotility.
Due to reorientation of prestin.
How is frequency specific information relayed from the hair cells to the cochlear nucleus?
hair cells synapse to the sensory neurons in the cochlear ganglion (spiral ganglion). Each ganglionc cells responds to stimulation at a particular frequency.
What is the pathology of senorineural hearing loss?
damage to sensory apparatus of Inner ear or to the vestibularcochlear nerve.
What can cause sensorineural hearing loss?
Loud noises
genetic mutations affecting Organ of Corti
aminoglycoside antibiotics = hair cell toxic
congenital diseases
acoustic neuroma
ageing.
How can cochlear implants compensate for hearing loss?
bypass dead hair cells and stimulate nerve fibres directly.
What is the role of the cochlear nucleus?
arrange neurons tonotopically (low frequencies = ventral)
What is the role of the doral cochlear nucleus?
processing high frequency sounds that produce interference wit the body due to the size of the sound wave.
What is the role of the superior olivary complex?
compare bilateral activity of cochlear nuclei
What is the role of the medial superior olive?
calculation of interaural time difference
What is the role of the lateral superior olive?
detect difference in intensity between two ears.
Interaural level difference compused to localise sounds in the horizontal plane.
How does the lateral superior olive detect differences in intensity between hears?
Comparing inhibitory and excitatory information from the contralateral and ipsilatreral sides respectively (how long they take)
How does the SOC protect against damage by loud sounds?
SOC sends feedback to hair cells - increased representation of signals in noise protects against damage.
How can sensorineural hearing loss occur (malfunctioning of auditory pathway to brain)
demyelination.
blast injuries upset excitation/inhibition balance.
What is the role of the inferior colloculus?
convergence of ascending auditory pathways.
Signal integration - precedence effect.
What is the role of the superior colliculus?
auditory and visual maps merge. Neurons are tuned to respond tostimuli with specific sound directions.
The auditory map here created is fundamental for reflexes
Where is the primary auditory cortex located?
superior bank of the temporal lobe
How is the AC mapped?
tonotopcially.
What is the role of the auditory complex?
response to complex sounds.
Diagram of route of ascending information.
