Neuro 8: Sound Conduction And Transduction Flashcards
What are main causes of hearing loss?
- loud, traumatic sounds
- genetic
- ageing
What is the hearing range of humans?
20 - 20000 hz
bel scale of sound defines :
it defines sound level
define pitch
pitch = perception of frequency
define timbre
timbre = what distinguishes 2 sounds at the same frequency + intensity
what does the 3 ossicles do?
what is the significance of this?
3 ossicles transmit vibration of tympanic memb to the conchea
- and acts to match the impedance and to reduce loss of energy as vibration
define impedance
impedance = easier of reluctance of a system in receiving energy from a source
define resonant frequency
resonant frequency = frequency at which impedance of system is minimal
What might cause conductive hearing loss?
- cerumen
- infection
- tumors
- fluid accumulation
What is a cochlea
liquid filled snail shaped organ
What causes vibration of basilar membrane?
the motion of the stapes generates pressure difference between 2 chambers of the cochlea
what is a stapes?
3rd ossicle.
What are the main components of the organ of corti
basilar + tectorial memb + (inner and Outer) hair cells + supporting cells
what does the basilar memb motion do to hair bundles?
it deflects hair bundles of hair cells
What is a basilar membrane?
Basilar memb = elastic structure that vibrates at diff position along its length –> in response to different frequencies
Describe how mechano - transduction occurs.
bending of stereo cilia –> towards tallest causes change in the internal voltage of cell
- which produces an electrical signal that travels to the brain
What feature connects the stereo cilia?
tip links
note: acts like small springs –> stretched by stereo cilia’s sliding
why is mechano-transduction considered an active process?
- because hair bundles have the capacity to do work
- the hair bundles actively complies wit the direction of the stimulus
- -> and measured stimulus becomes -ve
what are the 4 aspects of the active process of mechano-transduction?
- amplification
- frequency tuning
- compressive non linearity
- spontaneous otoacoustic emission
there are more / less outer hair cells than inner hair cells
there are more outer hair cells than inner hair cells
most of the afferent projection projects from outer hair cell/ inner hair cell
most efferent projection connects to the outer hair cell / inner hair cell
most of the afferent projection projects from inner hair cell
most efferent projection connects to the outer hair cell
How does electromobility occur?
due to reorientation of protein pristine, cell body shortens + elongates when their internal voltage is changed
Inner hair cell synapses with sensory neuron in the ______ ______
Inner hair cell synapses with sensory neuron in the spiral (cochlear) ganglion
the change in response to change of presynaptic voltage is proportional to the rate of _______ ________
the change in response to change of presynaptic voltage is proportional to the rate of neurotransmitter release
How might you deal with sensorineural hearing loss?
- cochlear implants
What is special about the cochlear nucleus?
- its the region where different neurons are arranged tonotopically
low frequency = ventral
high frequency = dorsal
What are the 2 main neurons in cochlear nucleus ?
a) T- stellate cells
b) bushy cells
what does the T-stellate cells do?
- it encodes sound freq + intensity of narrow band stimuli
what do bushy cells do?
- it carries information on timing of the inputs at every cycle
–> it provides resolution for encoding relative time of arrival of inputs to the 2 ears
What are the 2 mechanisms at which you know where the sound is coming from?
- time difference
2. interneuronal level difference
The superior olivary complex consists of what 2 main areas?
- medial superior olive
2. lateral superior olive
What is the function of the medial superior olive in hearing?
- it computes the interneuronal time difference
What is the function of the lateral superior olive in hearing?
- allows detection of intensity difference between the 2 ears
neurons are EXCITED by ipsilateral sound
neurons are INHIBITED by contralateral sound
neurons are EXCITED/INHIBITED by ipsilateral sound
neurons are INHIBITED/ EXCITED by contralateral sound
neurons are EXCITED by ipsilateral sound
neurons are INHIBITED by contralateral sound
what does the interneuronal level difference do?
it computes localization of sounds in the horizontal plane
Neurons from the MSO feedback to the hair cells (ipsilaterally /bilaterally)
neurones from the LSO feedback to the hair cells (ipsilaterally / bilaterally)
Neurons from the MSO feedback to the hair cells (bilaterally)
neurones from the LSO feedback to the hair cells (ipsilaterally)
With regards to hearing, what happens at the inferior colliculus? What does it do?
inferior colliculus:
- site where responses from diff frequency merges
- closer to the cortex –> it is more responsive to complex sounds
With regards to hearing, what happens at the superior colliculus? What does it do?
superior colliculus:
- site where auditory + visual maps merge
- neurons turn to respond to stimuli with specific sound directions
–> so helps orientate head + eye reflex movements in response to acoustic stimuli
note:
at primary auditory cortex :
- loudness / rate / frequency modulation is mapped
- also TONOTOPICALLY mapped
-
what allows location of sound in the vertical plane?
dorsal cochlear nucleus
what allows location of sound in the horizontal plane?
interneuronal level difference
Describe how the cochlea functions.
how is sound conducted through the cochlea? (step by step)
- Tympanic membrane vibrates
- Vibration is conducted + amplified to oval window
- This vibration induces pressure wave in perilymph (in scala Vestibuli)
- Which in turn causes scala Media to vibrate
- Which causes basilar membrane to vibrate
- The round window then vibrates to equalise pressure in the cochlea
What is the function of organ of corti?
- Organ of Corti = sense organ of cochlea
- Converts sound signals into nerve impulse that are transmitted to the brain via cochlear nerve
What is the function of the inner hair cells
+
are they in contact with tectorial memb?
- Not in contact with tectorial memb
- Sends impulse to brain
- Has stereocilia –> which moves in response to movement of endolymph in scala media
Describe the features and function of outer hair cells.
+
are they in contact with tectorial memb?
- Found in groups of 3
- In contact with tectorial memb
- They receive input from the brain
- Can expand + contract to amplify amount of vibration
- Damage = sensorineuronal hearing loss.
- Describe what happens when the basilar membrane is displaced upwards.
- When basilar memb = displaced upwards
- Causes depolarisation
- Stereocilia moves away from modiolus
- K+ channels open
- K+ enters from endolymph
- Describe what happens when the basilar membrane is displaced downwards.
- When basilar memb = displaced downwards
- Hyperpolarisation occurs
- Sterocilia moves towards modiolus
- K+ channels close
- Describe the difference in K+ and Na+ concentration in the different compartments of the cochlea.
- Scala media = High K+ / Low Na+
- Scala Tympani = High Na+ / Low K+
- Describe the auditory pathway from the cochlea to the primary auditory cortex
Spiral ganglion --> cochlear nuclei --> superior olive --> inf colliculus --> medial geniculate nucleus --> primary auditory cortex
- What is the secondary auditory cortex responsible for?
- Responsible for sounds coming on/ off
- Responsible for duration of sound
How do you localise short sound burst?
Interneural time delay
How do you localise continuous sound?
Interneural intensity difference
What is conductive hearing loss?
- Disease of middle ear –> damages ossicles / stiffens joint
- Amplification system = affected
- Causing conductive hearing loss
What is sensorineural hearing loss and what can it be caused by?
- Sensorineural hearing loss = cochlea / cochlear nerve is damaged
- So signal transmitted to the primary auditory complex = reduced or lost
- Can occur due to acoustic schwannoma/ cerebellar tumours pressing on cochlear nerve
what is - Presbyacusis ?
loss of hearing due to the death of hair cells in normal ageing
