The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM...
-
date post
21-Dec-2015 -
Category
Documents
-
view
228 -
download
0
Transcript of The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM...
![Page 1: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/1.jpg)
The auditory system
Structure and function
![Page 2: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/2.jpg)
Objective
• Recap – outer, middle and inner ear to BM response
• To continue the hearing process from the inner ear to the brain
• How the physical properties of sound, such as frequency and amplitude, are represented in the auditory system
![Page 3: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/3.jpg)
![Page 4: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/4.jpg)
Organ of Corti
• The organ of corti is the hearing sense organ and lies on the BM
• It consists of supporting cells and hair cells• 2 groups of hair cells: inner and outer hair cells• Protruding from each hair cell are hairs called
stereocilia• The tectorial membrane lies above the stereocilia –
shearing motion between BM and tectorial membrane – causes stereocilia to be displaced
![Page 5: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/5.jpg)
![Page 6: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/6.jpg)
![Page 7: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/7.jpg)
Inner hair cells
• Function is to convert BM mechanical movement into neural activity – achieved in the following way (Moore, 2004):
• The stereocilia are joined by fine links called ‘tip links’.
• Deflection of the stereocilia leads to the opening of “transduction channels”.
• Flow of potassium ions into the hair cell – voltage difference between the inside and outside of the hair cell.
![Page 8: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/8.jpg)
Inner hair cells
• Causes the release of neurotransmitter and the initiation of action potentials in the neurons of the audtiory nerve.
• Action potential – ‘firing’ of a neuron. Propagation is in one direction only down the length of the axon
• Most of the afferent neurons make contact with the inner hair cells
• Possibly all information about the input sound is conveyed via the inner hair cells
![Page 9: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/9.jpg)
Outer hair cells
• Have a role in achieving high sensitivity and sharp tuning
• Most of the efferent neurons synapse directly with the outer hair cells
• Efferent neurons carry information from higher auditory system to cochlea
• Afferent neurons carry information from the cochlea to the higher auditory system
![Page 10: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/10.jpg)
Auditory nerve
• Consists of vestibular and cochlear nerve
• Cochlear nerve – the axon fibres of neurons whose cell bodies are in the spiral ganglion of the cochlea
• dendrites of these neurons synapse with the hair cells – dendrites information receivers
![Page 11: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/11.jpg)
Afferent auditory nerve
• Transmits hearing information from cochlea to central nervous system
• Important findings from recording impulses in single auditory nerve fibres.
• Spontaneous firing, frequency selectivity of fibres, phase locking
![Page 12: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/12.jpg)
Spontaneous firing rates
• Firing in the absence of sound stimulation• Fibres divided into three groups based on their
spontaneous firing rates• High, medium and low spontaneous rate fibres • High spontaneous rate fibres generally have lower
thresholds and smaller dynamic ranges than medium or low spontaneous rate fibres
![Page 13: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/13.jpg)
Frequency selectivity
• Fibres show frequency selectivity – as fibres responding to activity at restricted regions of the BM
• Characteristic frequency (CF) – frequency at which the threshold of a fibre is lowest
• Fibres with high CF found in periphery of auditory nerve – orderly decrease in CF towards centre of the auditory nerve
• Tonotopic organisation – place representation of frequency on BM maintained in auditory nerve
![Page 14: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/14.jpg)
Phase locking
• The firing of a neuron at one distinct point (phase) in the period of a sound wave.
• temporal regularity in the firing pattern of a neuron in response to a periodic stimulus
• upper limit: 4-5 kHz• May not fire on every cycle, but will occur at
roughly the same phase of the waveform• Time intervals between spikes are approximately
integer multiples of the period of the waveform• an indicator of the period of the waveform
![Page 15: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/15.jpg)
![Page 16: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/16.jpg)
The brainstem and auditory cortex
• Binaural perceptions, such as our ability to localise sounds depends on the interaction of information from both ears
• The information from both auditory nerves is first combined in the brainstem
• Highly complex system, many of the neural pathways within and between the nuclei have yet to be investigated
• Brainstem nuclei: cochlear nucleus, superior olivary nucleus, inferior colliculus, medial geniculate body.
![Page 17: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/17.jpg)
![Page 18: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/18.jpg)
• Tonotopic organisation of frequency is preserved – neurons aligned respective to the frequencies to which they are most sensitive
• The responses of neurons at higher levels in the auditory system – not as well studied as responses in the auditory nerve
• Some neurons in the auditory cortex only respond to complex stimuli, or to stimuli with time varying characteristics
![Page 19: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/19.jpg)
Cochlear nucleus
• The auditory nerve carries signals from the cochlea to the cochlear nucleus in the brainstem.
• First brainstem nucleus at which afferent auditory nerve fibres synapse
• Monaural – input from same side ear only• 3 parts – anteroventral, posteroventral, dorsal• Not clear what its function in auditory processing
is. – tonotopic organisation of frequency
![Page 20: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/20.jpg)
Superior olivary complex
• Binaural - Here the inputs from both ears converge
• Important for sound localisation
• Use of timing and intensity differences
![Page 21: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/21.jpg)
Inferior colliculus
• Receives inputs from the olivary complex and the cochlear nucleus
• Some cells are monaural, some are binaural• Much (but not all) of the input to the inferior
colliculus comes from the opposite ear• May function in sound localisation, and in
combining information from lower areas in the brainstem
![Page 22: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/22.jpg)
Medial geniculate nucleus
• Last stop in the auditory pathway before the cerebral cortex.
• 2-way information flow between medial geniculate and the auditory cortex
• Feedback from the brain is tightly integrated with sensory information flowing up to the brain
![Page 23: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/23.jpg)
Auditory cortex
• Primary auditory cortex (A1) – the first area within the temporal lobes of the brain responsible for processing acoustic information
• Each cochlea has input to each auditory cortex• Tonotopic organisation of frequency is maintained
in the A1• 2-way information between cortex and brainstem
![Page 24: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/24.jpg)
• No response to steady, unchanging tones – pure tones
• Some cortical neurons respond to tones increasing or decreasing in frequency
• Some respond to amplitude variations
![Page 25: The auditory system Structure and function. Objective Recap – outer, middle and inner ear to BM response To continue the hearing process from the inner.](https://reader036.fdocuments.net/reader036/viewer/2022062421/56649d605503460f94a41aef/html5/thumbnails/25.jpg)
• Next: frequency resolution (selectivity) and pitch perception, reading material