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BMS1052 > SOMATOSENSATION: HEARING > Flashcards

SOMATOSENSATION: HEARING Flashcards

1
Q

What does the pinna do?

A
  • Sound filter and funnel
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2
Q

What are the ossicles?

A
  • Middle Ear bones
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3
Q

What is the cochlear?

A
  • Fluid filled bony structure containing receptor neurons
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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
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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
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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
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7
Q

Where is the oval window located?

A
  • membrane covering hole in bone of skull
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8
Q

Where is the cochlear located?

A
  • Behind the oval window
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9
Q

What are the general steps in auditroy pathway?

A
  1. Sound wave move tympanic membrane
  2. Tympanic membrane moves ossicles
  3. Ossicles move membrane at oval window
  4. Motion at oval window moves fluid in cochlea
  5. Movement of fluid in cochlea causes response in sensory neurons
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10
Q

What structures make up the outer ear?

A
  • From pinna to tympanic membrane
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11
Q

What structures make up the middle ear?

A
  • Tympanic membrane and ossicles
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12
Q

What constitutes the inner ear?

A
  • The apparatus medial to oval window (cochlear etc) 1
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13
Q

What is A1?

A
  • Primary auditory cortex that Medial Geniculate Nucleus projects to
  • Located in temporal lobe
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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
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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
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16
Q

Which two membrane covered holes are at the base of the cochlea?

A
  • The oval window and the reound window
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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
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18
Q

What does the Organ of Corti contain?

A
  • Contains the auditory receptor neurons
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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.
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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.
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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
Q

What does sound cause in terms of the footplate of teh stapes?

A
  • 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
Q

What does the distance the wave travels up the basilar membrane depend on ?

A
  • the frequency of the sound
27
Q

What does the basilar membrane do if the sound frequency is high?

A
  • Stiffer base of membrane will vibrate and wave won’t propagate very far
28
Q

What does the basilar membrane do if the sound frequency is low?

A
  • Sound waves will travel all the way up to the floppy apex of membrane BEFORE most of the energy is dissipated.
29
Q

What is tonotopy?

A
  • Systematic organisation of sound frequency within auditory structure (different locations of basilar q membrane are maximally deformed at different sound frequencies)
30
Q

In which structures do tonotopic maps exist?

A
  • Basilar membrane
  • Each auditory relay nuclei
  • MGN
  • Auditory cortex
31
Q

What does the Organ of Corti consist of?

A
  • Hair cells (containing stereocilia)- specialised epithelial cells (NOT NEURONS)
  • rods of Corti
  • various supporting cells
32
Q

Which action of the cilia allows for the transduction of sound into neural signal?

A
  • The BENDING of cilia (flexing of basilar membrane leads to bending of stereocilia)
33
Q

What does the tectorial membrane do?

A
  • Holds the tips of the outer hair cell stereocilia
34
Q

What filaments make stereocilia ‘rigid rods’ in sond transduction?

A
  • Actin Filaments which make them only bend at the base (where they attach to top of hair cell)
35
Q

What causes all the stereocilia to move as a whole unit?

A
  • the crosslink filaments
36
Q

How are stereocilia in a hair cell arranged?

A
  • In height order
37
Q

What is the structure called that is believed to connect the protein channel to the upper wall of adjacent cilia?

A
  • Tip Links
38
Q

Where are the cell bodies of axons (of neurons) for the vestibulocochlear nerve?

A
  • Spiral ganglion
39
Q

Which structure is the first in the auditory pathway to fire APs?

A
  • 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
Q

How many inputs from inner hair cells does one spiral ganglion fiber receive?

A
  • Only one inner hair cell (each inner hair cell feeds onto 10 spiral ganglion neurites)
41
Q

Does one spinal ganglion fibre synapse with multiple outer hair cells?

A
  • YES!
42
Q

Where does most of the information from the cochlear come from?

A
  • The INNER HAIR CELLS (not outer)
43
Q

Are spiral ganglion cells frequency tuned?

A
  • YES!
44
Q

What 2 ways is the information about sound intensity coded?

A
  • Firing rates of neurons

- Number of active neurons

45
Q

What characteristic frequencies do auditory nerve fibres connected to hair cells near the apical basilar membrane have?

A
  • Low characteristic frequencies
46
Q

What is phase locking?

A
  • 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
Q

How are different sound frequencies represented at low frequencies?

A
  • Phase locking
48
Q

How are different sound frequencies represented at intermediate frequencies?

A
  • BOTH phase locking AND tonotophy
49
Q

How are different sound frequencies represented at high frequencies?

A
  • Tonotopy (above 5HZ)
50
Q

What is ILD (InterAuralDifference)?

A
  • 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
Q

What is ITD?

A

(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
Q

What does AP rate in spiral ganglion cells depend on?

A
  • Sound frequency (pitch) and sound intensity (loudness)

BMS1052 (14 decks)

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