Lecture 9: Auditory system Flashcards
N.C
Which organ decomposes sound intto separate frequencies?
Cochlea (slakkenhuis)
What is a Fourier series
Sum of sines and cosines –> sound/waveform
What are the sensory receptors of the auditory system?
Hair cells in the organ of Corti
What is tonopy?
Spatial mapping of sounds frequencies in the auditory system.
How is the tonopy mapped in the basilar membrane?
- Base –> high frequencies
- Apex –> low frequencies
How does the cochlea create tonotopy?
The changing width and stiffness of the basilar membrane.
Where does transduction in the cochlea happen?
In the organ of Corti where hair cells are located. They convert acoustic stimuli into electrochemical signals
What is the difference between inner and outer hair cells?
- Inner hair cells can only transduce mechanical stimuli to electrochemcial, making them the real sensory transducers
- Outer hair cells can transduce from mechanical to electrochemical and the other way around
What happends when a travelling wave hits the basilar membrane?
The basilar membrane will move. This will cause relative movement between basilar membrane and tectorial membrane, causing stereocilia to bend. Bending of the stereocilia triggers an electrical response in the hair cells
What happens when there is deflection towards the shortest stereocilia and if towards the longest stereocilia?
Towards shortest stereocilia: hyperpolarization
Towards longest stereocilia:
depolarization
What is the AC and DC component of a (stimulus) signal?
AC component is the part that fluctuates/changes over time
DC component is the part that stay steady/constant that remains unchanged over time
Which claim about sensory transduction of hair cells is incorrect?
- The AC component of hair cells is small at high stimulus frequencies
- Deflection of the cilia towards the longest cilium produces depolarization
- The electrical activity initiated by the tip links is transferred to the vesicular release sites
- The firing frequency (number of actoin potentials) in hair cells depends on the frequency of the auditory stimulus
4
What is the cochlear amplifier?
Sharp peak in the cochlea - increase sensitivity to low-intensity sounds + improved frequency resolution
Which motor protein in the lateral membrane of outer hair cells cause mobility and what does it enhance?
Prestin, enhances vibration of basilar membrane
How does the cochlear amplifier work in OHC?
It is a positive feedback mechanism:
Voltage dependent prestin contract, making the distance between the basilar membrane and the reticular lamina smaller. This amplifies the amplitude of the travelling wave across the basilar membrane, sharpening the sound.
What type of ganglion cells synapse with hair cells and what do their axons form?
Spiral ganglion cells, axons form the VIII cranial nerve/auditory nerve
They are bipolar neurons
What should be encoded in de auditory system?
Intensity, location, frequency = submodality
What is the characteristic frequency?
Frequency with lowest input required
Why can the cochlea and nerve be considered as a filter bank?
each inner hair cell + coupled nerve fibers analyzes narrow band of frequencies; the entire auditory nerve convers the entire audible frequency range
How is intensity encoded?
Firing frequency & number of neurons
1. Number of APs per second, that increases with the intensity of the input.
2. The number of neurons firing, that increases with the intensity of the input
NOTE: increase intensity –> increases number of spikes
How is frequency encoded?
Place (tonotopy)
Frequency (phase-locking)
Which of the following sttements about the auditory nerve fibers is false?
- Afferent fibers receive input from inner hair cells.
- High frequency fibers can respond well to stimuli at frequencies in the rang of 10 to 20 kHz in humans.
- The characteristics frequency of the hair cells systematicaly varies along the length of the cochlear axis.
- One ganglion cell makes contact with one outer hair cell.
4
What is the anatomy of the superior olivary complex?
- Medial nucleus of the trapezoid body (MNTB)
- Lateral superior olive (LSO)
- Medial superior olive (MSO)
What is the function of the medial and lateral superior olive?
MSO: ITDs –> interaural time differences – MSO = for low frequencies
LSO: ILDs –> interaural level differences – LSO is for high frequencies
Is there a time/phase difference between the ears when..
- Distance from the sound source for both ears is equal
- Source is closer to one ear than the other
- no
- yes
What happens with the cells in the LSO when a speaker makes a sound at the left ear?
Cells in the LSO receive an excitatory activation from the left ear (ipsilateral ear).
Cells in the LSO receive an inhibitory activation from the right ear (contralateral)
It gives difference in sound intensity for the particular frequency
NOTE: LSO transmits result to contralateral hemisphere
What is the pathway from the superior olivary nucleus to the auditory cortex?
Cochlear nucleus (medulla) –> superior olivary nucleus –> medial geniculate nucleus (thalamus) –> auditory cortex
What is the first brain structure in the auditory system that receives information from both left and right ear?
Superior olive
