Hearing Smell Taste Lecture- Hearing

Question 1

Soundwaves

Amplitude

Answer 1

• measured as sound pressure
• =loudness
• Height of a wave as measured from the peak to the trough

Question 2

Sound waves

Frequency

Answer 2

• measured in Hertz (Hz)
• frequency = pitch
• most peoplel detect 20-20,000 Hz
• increases amount of waves per unit time

Question 3

How does the brain interpret sound?

Answer 3

Mechanical energy of sound waves transducted into neuronal electrical activity

Question 4

What is sensory transduction?

Answer 4

the conversion of energy from a stimulus into a change in membrane potential

Question 5

Outer ear

What is the pinna’s function?

Answer 5

The pinna funnels sound waves into the ear canal

Question 6

How does sound travel from air to ear?

Answer 6

• once the pinna funnels sound waves into the ear canal, sound waves progagate down the canal to the tympanic membrane (aka ear drum)

the tympanic membrane separates the outer ear from the middle ear

Question 7

middle ear

What happens after sound waves reach the tympanic membrane?

Answer 7

• vibrations in the tympanic membrane cause 3 ossicles (malleus, incus and stapes) to move

Question 8

middle ear

What are ossicles?

Answer 8

• tiny bones in the middle ear that serve to transmit sounds from air to cochlea
• absence would constitute a moderate to severe hearing loss

Question 9

middle ear

What do the Tympani and Stapedius muscle do?

Answer 9

• control contact between ossicles to protect from loud sounds
• also mute self-made sounds (ex. swallow)

Question 10

middle ear

Where is the stapedius muscle located?

Answer 10

• Stapedius muscle is caudal/inferior to the stapes bone

Question 11

inner ear

What does the stapes contact? What is the function of this?

Answer 11

• stapes contacts the oval window
• the oval window transfers vibrations to 3 fluid filled canals in cochlea

Question 12

inner ear

What does the cochlea look like?

Answer 12

small and coiled

Question 13

inner ear

What separates the cochlea’s canals?

Answer 13

the basilar membrane

Question 14

inner ear

Basilar membrane function

Answer 14

• Vibrates- Different areas are sensitive to specific frequencies
• high freq at narrow stiff base (when cochlea unrolled)
• low freq at wide, floppy apex (when cochlea unrolled)

Question 15

What is a tonotopic map?

Answer 15

an ordered map of frequencies created by the responding of neurons within structures in the auditory system

Question 16

inner ear/tuning curves of hair cells

Where are hair cells located?

Answer 16

on the thin basilar membrane in the cochlea of the inner ear

Question 17

What do hair cells have?

Answer 17

• distinctive receptive fields, or tuning curves
• a tuning curve provides a three dimensional plot of the firing rate of hair cells over a restricted range of stimulus frequencies and intensities

Question 18

The more sensitive the hair cell…?

Answer 18

the greater the response (as visualized on tonotopic map of frequency!)

Question 19

cochlea

What does the Organ of Corti contain and where is it found?

Answer 19

• located on basilar membrane (sits on top)
• contains inner and outer hair cells

Question 20

What do inner hair cells do? Where are they located?

Answer 20

• they detect sound
• part of organ of corti
• superior to nerve fibers
• to right of outer hair cell (closer to the brain)

Question 21

What do outer hair cells do?

Answer 21

• amplify low-level sounds to help discriminate between similar frequencies
• located more outside than inner hair cells in regards to brain location

Question 22

cochlea- organ of corti

Together, what do hair cells do?

Answer 22

• transduce sound waves into neuronal activity
• synapse with auditory nerve fibers
• have 50-200 stereocilia (hairs required for hearing and balance)

Question 23

What are tip links? Where are they located and what do they do?

Answer 23

• Tip links are extracellular tethers that link sterocilia
• They open ion channels when sterocilia are bent

Question 24

Transduction of sound into electrical transmission

Answer 24

• On the inner hair cells, vibrations bend/displace sterocilia
• tip links open ion channels
• Ca2+ and K+ depolarize inner hair cell
• Glutamate is released onto auditory nerve

Question 25

Pathway from hair cells to brain

Answer 25

1. Hair cells synapse onto vestibulocochlear nerve (8th)
2. 8th nerve synapses onto cochlear nucleus in brain stem
3. Info travels to both superior olivary nuclei (most info crosses midline)
4. Inferior colliculus (primary auditory centers of midbrain), then medial geniculate nucleus (thalamus), then auditory cortex

Question 26

inferior colliculus

Answer 26

• tonotopic map- critical for sound localization
• procsses intensity, frequency, and duration of sound

Question 27

auditory cortex function

Answer 27

• identifies complex sounds that have many sub-parts (eg vocalizations)
• tonotopic map (corresponds to apex to base of cochlea as you move caudally

Question 28

Where is the primary auditory cortex located?

Answer 28

temporal lobe

Question 29

conduction deafness

Answer 29

disorders of the outer/middle ear that prevent vibrations from reaching the cochlea

Question 30

sensorineural deafness

Answer 30

originates from cochlear or auditory nerve lesions; hereditary disease of hair cells

Question 31

What is central deafness?

Answer 31

hearing loss caused by brain lesions (such as stroke) with complex results

Question 32

Pathway to brain

What do hair cells synapse onto?

Answer 32

• the vestibulocochlear nerve (8th)
• located on the cochlea

Question 33

pathway to brain

What does the 8th nerve synapse onto?

Answer 33

• the cochlear nucleus in the brain stem

Question 34

pathway to brain

What happens after info travels to the cochlear nucleus?

Answer 34

• it travels to both superior olviary nuclei
• most info crosses the midline

Question 35

After reaching both superior olivary nuclei, where does info go?

Answer 35

• to the inferior colliculus (primary auditory centers of midbrain)
• then to the medial geniculate nucleus (thalamus)
• then to the auditory cortex (temporal lobe)

Question 36

where is the medial geniculate nucleus located?

Answer 36

the thalamus

Question 37

Where is the inferior colliculus located?

Answer 37

midbrain (is the primary auditory center of the midbrain)

Question 38

What are the three ossicles?

Answer 38

• malleus
• incus
• stapes