What is the energy picked up by the receptors involved in hearing?
-vibrations in the air
What are the receptors involved in hearing?
-inner hair cells
What is the range of the inner hair cells?
-20-20 000 Hz
What is the sensitivity and dynamic range of the hearing receptors?
picometers to 100dB (dB= log scale!) (picometers= changes in movement on that scale can lead to detection in auditory system)
What is the receptive field of the inner hair cells?
-certain frequency of sounds, quite large -peak of the wave
What are the 4 key concepts in sensory system detection?
1.Transduction(how is energy captured and transformed) 2.Receptive field (what stimuli can change neuronal activity) 3.Sensitivity and range 4. Resolution (spatial and temporal= what can a system do?)
What is the stimulus picked up by the hearing system?
-compressed and rarefied shells of air -something makes air move= vibrations -compressed= positive on the sine wave and rarefied= negative on the sine wave
-in reality we don't hear tone sine waves, most sounds are very complex, lot of frequencies together,
What is the perception of wavelength?
-distance between wave peaks -PITCH
What is the perception of amplitude?
-how high a wave is -LOUDNESS
What is the perception of waveform?
-the wave will not be a perfect sin wave -TONE/TIMBRE
Why are people attuned to music?
-music based on scale -speech too -similar to speech maybe that is why we can detect such nuances in sound= as understanding speech is important for social life and function
What is the functional significance of the pinna?
-pinna has functional significance= if sound from in front of you, and same sounding sound from behind you, how do you detect where each comes from?= part of that ambiguity is resolved by pinna= amplify high frequencies from high up -filtering of sounds pina and concha as well
What does the tympanic membrane do?
-ike a drum, vibrates with sympathy of the waves coming in
What are the parts of the outer ear?
-external auditory meatus
What are the parts of the middle ear?
-middle ear filled with air still
What is the function of the middle ear?
-the tympanic membrane and the malleus, incus and stapes translate the vibrations in the air to vibrations in fluid -it is very hard to transmit energy through water(like around lakes how you can hear from far= as the sound is not absorbed by the water!) -the middle ear= mechanical lever system= more energy over a smaller area= makes it easier for energy to get to the fluid
What is the major part of the inner ear?
-fluid filled cochlea and vestibular apparatus
What is the compartment structure of the cochlea?
-fluid filled 3 compartments
-(1.scala vestibuli, 2. scala media, 3. scala tympani)
-in the scala media= Organ of Corti,inner and outer hair cells
-the scala vestibuli and tympani are connected at the end
-in the middle is the scala media -the upper bit of scala tympani= basilar membrane
-in the scala media, tectorial membrane
What are the three compartments of the cochlea?
1.scala vestibuli 2. scala media 3. scala tympani
Do the hair cells have hair?
What converts the vibrations to a neural signal?
-inner hair cells -afferent function
What are outer hair cells for?
-role in maintaining and changing the stiffness of the basilar membrane -can contract, and therefore act as motor units that amplify the movement of the basilar membrane in response to a stimulus -have efferent function
How is the cochlea organised in terms of frequencies?
-different parts of the cochlea correspond to different frequencies, this is because the stiffness of the basilar membrane differs along the cochlea, so it will be moved depending on the frequency
-high frequencies resonate at the base
-low frequencies resonate at the apex
What is the ionic environment in the cochlear compartments?
-scala tympani and vestibuli= normal (lot of Na+) -scala media= very high K+ (potassium) concentration
Why does the scala media have such high K+ ECF concentration?
-has a special organ= stria vascularis -this has special pumps K+ into the extracellular medium -125mV difference!
How does the inner ear work?
-get vibrations from the middle ear, these are transferred along the basilar membrane and that makes it move, the hair cells that are close to the tectorial membrane move with the basilar membrane and this movement bends them in relation to the tectorial membrane= shearing force
-the basilar membrane bends= so it is movement up and down (the upwards and downwards phase)
-the bending of the inner hair cells opens mechanically gated K+ channels and K+ goes into the inner hair cell= DEPOLARISATION
-then voltage gated channels Ca2+ open (if the membrane is depolarised enough) that activates the vesicles in the inner hair cell and they fuse with the membrane and release the transmitter into the synaptic cleft with the neuron going to the brain (afferent nerve)
-also tip links= connect the hair cell tips
What is connected to the oval and round window?
-round= scala tympani -oval scala vestibuli
Up to what frequency do the hair cells faithfully follow the vibrations?
-up to 1000Hz
-over that get DC component
What is the mechanoelectrical transduction in hearing mediated by?
What are the response properties of the auditory nerve fibres?
frequency range= the receptive field
-what freq excite that hair cell? receptive field is quite large, respond over a range of freq but have prefernece -place code= when bit activated corresponds to sound
What does it mean that the auditory nerves are phase locked with the frequencies they respond to?
phase locked, the neuron activity
-not just the freq but also phase, when the freq is changing
What is the auditory pathway like?
-very complex -lot of crossovers -thalamic relay and cortical representation
How can we tell which direction is a sound coming from?
-the MSO (medial olivary complex= in the brain stem) computes the location of a sound by interaural differences(the difference of when the sound gets to one ear and the other ear)
-MSO gets maximal input when if both ears stimulated simultaneously (C)
-gets input at different times from the ears when sound closer to one
What is the other way of recognising where a sound is coming from (LSO)?
-LSO (lateral superior olive) encode sound location through interaural intensity differences
-uses intensity of sound, from one side to the other (the difference)
-each of the neurons of the LSO receives input from both of the ears, both excitatory and inhibitory = if the sound dead at front then the excitation will be equal to inhibition
-if sound in the right= then the inhibition and excitation is unequal= get more excitation from the right -mutual inhibition
-can tell from which side the sound is coming from
What is the organisation of the human auditory cortex?
-map of frequencies in the cortex, same as in the thalamus and the basilar membrane
What is Wernicke's area for?