SOMATOSENSATION: HEARING Flashcards
1
Q
What does the pinna do?
A
- Sound filter and funnel
2
Q
What are the ossicles?
A
- Middle Ear bones
3
Q
What is the cochlear?
A
- Fluid filled bony structure containing receptor neurons
4
Q
What is the function of the outer ear?
A
- To funnel sound waves toward the tympanic membrane(ear drum) and filters sounds in direction dependent manner
5
Q
What occurs in bone conduction in terms of transferring of vibrations?
A
- Sound directly vibrates bones of the skull, transferring vibrations directly to the cochlear
6
Q
What is the function of the ossicles?
A
- Connected to medial surface of tympanic membrane
- Located in small air filled chamber
- Transfer movements of tympanic membrane into movements of the oval window
7
Q
Where is the oval window located?
A
- membrane covering hole in bone of skull
8
Q
Where is the cochlear located?
A
- Behind the oval window
9
Q
What are the general steps in auditroy pathway?
A
- Sound wave move tympanic membrane
- Tympanic membrane moves ossicles
- Ossicles move membrane at oval window
- Motion at oval window moves fluid in cochlea
- Movement of fluid in cochlea causes response in sensory neurons
10
Q
What structures make up the outer ear?
A
- From pinna to tympanic membrane
11
Q
What structures make up the middle ear?
A
- Tympanic membrane and ossicles
12
Q
What constitutes the inner ear?
A
- The apparatus medial to oval window (cochlear etc) 1
13
Q
What is A1?
A
- Primary auditory cortex that Medial Geniculate Nucleus projects to
- Located in temporal lobe
14
Q
What structure allows the middle ear to be continuous with the air in the nasal cavities?
A
- Eustachian tube
- But valve usually keeps it closed
- This helps keep ear at same pressure despite changing pressure around the ear
- Air pressure is higher inside middle air when ascending on aeroplane and opening tube will relieve pressure
15
Q
What is the attenuation reflex?
A
- When the muscles attached to ossicles (tensor tympani and stapedius muscle) CONTRACT to cause the ossicles to become rigid and not transmit any vibrations to oval window.
- This protects inner ear from damage and reflex is higher in low frequencies
- Also may adapt it to continuous sound at high intensities
16
Q
Which two membrane covered holes are at the base of the cochlea?
A
- The oval window and the reound window
17
Q
Which 3 fluid filled chambers is the cochlea divided into?
A
- Scala vestibuli
- Sala media
- Scala tympani
- Ressiners membrane separates the vestibuli from the media
- Basilar membrane separates the scala tympani from scala media
18
Q
What does the Organ of Corti contain?
A
- Contains the auditory receptor neurons
19
Q
What absorbs Na+ from and secretes K+ into the endolymph via active transport?
A
- The Stria Vascularis (endothelium lining one wall of scala media and contacting endolymph.
20
Q
What is the fluid called in the scala tympani and vestibuli?
A
- The perilymph
- Concentration similar to CSF
- Low K+ and high Na+ conc.
21
Q
What is the scala media filled with?
A
- Endolymph
- Unusual concentration as resembles intracellular fluid; High K+ conc. and low Na+ conc.
22
Q
What does inward motion at the oval window cause?
A
- Pushes perilymph into scala vestibuli
- This causes membrane at round window to bulge out
23
Q
What does the basilar membrane do in response to sound?
A
It is flexible so in repsonse to sound it bends!
24
Q
What is the base of the basilar membrane more sensitive to?
A
- Higher frequencies
- Stiffer and more narrow than apex of basilar membrane
25
What does sound cause in terms of the footplate of teh stapes?
- Continual push pull motion of footplate like tiny piston (pull- reverses pressure gradient) (push: perilymph displaced within scaa vestibuli and endolymph displaced within scala media)
26
What does the distance the wave travels up the basilar membrane depend on ?
- the frequency of the sound
27
What does the basilar membrane do if the sound frequency is high?
- Stiffer base of membrane will vibrate and wave won't propagate very far
28
What does the basilar membrane do if the sound frequency is low?
- Sound waves will travel all the way up to the floppy apex of membrane BEFORE most of the energy is dissipated.
29
What is tonotopy?
- Systematic organisation of sound frequency within auditory structure (different locations of basilar q membrane are maximally deformed at different sound frequencies)
30
In which structures do tonotopic maps exist?
- Basilar membrane
- Each auditory relay nuclei
- MGN
- Auditory cortex
31
What does the Organ of Corti consist of?
- Hair cells (containing stereocilia)- specialised epithelial cells (NOT NEURONS)
- rods of Corti
- various supporting cells
32
Which action of the cilia allows for the transduction of sound into neural signal?
- The BENDING of cilia (flexing of basilar membrane leads to bending of stereocilia)
33
What does the tectorial membrane do?
- Holds the tips of the outer hair cell stereocilia
34
What filaments make stereocilia 'rigid rods' in sond transduction?
- Actin Filaments which make them only bend at the base (where they attach to top of hair cell)
35
What causes all the stereocilia to move as a whole unit?
- the crosslink filaments
36
How are stereocilia in a hair cell arranged?
- In height order
37
What is the structure called that is believed to connect the protein channel to the upper wall of adjacent cilia?
- Tip Links
38
Where are the cell bodies of axons (of neurons) for the vestibulocochlear nerve?
- Spiral ganglion
39
Which structure is the first in the auditory pathway to fire APs?
- The spinal ganglion neurons (most communicate with inner hair cells even though there are less of them- so majority of information leaving cochlea comes from INNER HAIR CELLS )
40
How many inputs from inner hair cells does one spiral ganglion fiber receive?
- Only one inner hair cell (each inner hair cell feeds onto 10 spiral ganglion neurites)
41
Does one spinal ganglion fibre synapse with multiple outer hair cells?
- YES!
42
Where does most of the information from the cochlear come from?
- The INNER HAIR CELLS (not outer)
43
Are spiral ganglion cells frequency tuned?
- YES!
44
What 2 ways is the information about sound intensity coded?
- Firing rates of neurons
| - Number of active neurons
45
What characteristic frequencies do auditory nerve fibres connected to hair cells near the apical basilar membrane have?
- Low characteristic frequencies
46
What is phase locking?
- Consistent firing of a cell at the same phase of a sound wave (action potential would only fire at the same phase of the sound wave-peaks or troguhs- so frequency of sound is same as freq. of neuron's APs)
- BUT at high frequencies this doesn't occur
47
How are different sound frequencies represented at low frequencies?
- Phase locking
48
How are different sound frequencies represented at intermediate frequencies?
- BOTH phase locking AND tonotophy
49
How are different sound frequencies represented at high frequencies?
- Tonotopy (above 5HZ)
50
What is ILD (InterAuralDifference)?
- Relates to how the brain localizes sound at high frequencies
- Head casts a shadow to sound waves so if sound comes to right, then right ear will hear a higher intensity than left
- Neurons sensitive to the differences in intensity can use the info (above) to work out where sound is coming from
- 2000-20 000 Hz
ONLY HIGH FREQUENCIES
51
What is ITD?
(InterAural Time Delay)
- Interaural Time Delay
- If sound comes from one side, it will reach the ear on that side first with a small delay until it reaches other ear
- Detected by specialized neurons in brain stem, delay enables us to locate the source of the sound in horizontal plane
- Helps with locating source of sound
- If sound is coming in front, there will be no delay
LOW FREQUENCIES
52
What does AP rate in spiral ganglion cells depend on?
- Sound frequency (pitch) and sound intensity (loudness)
