NEUR 0010 - Chapter 11

Question 1

What is the outer ear?

Answer 1

Pinna and auditory canal

Question 2

What is the middle ear?

Answer 2

TM and ossicles

Question 3

What is the inner ear?

Answer 3

Oval window and structures medial to it; cochlea

Question 4

What is the thalamic relay center for audition (like the LGN)?

Answer 4

MGN

Question 5

Where is the primary auditory cortex located?

Answer 5

Temporal lobe

Question 6

What is the Eustachian tube?

Answer 6

Usually closed; descends from the ossicles in the middle ear; continuous with nasal cavity

Question 7

Why is it a “problem” that the cochlea is fluid-filled?

Answer 7

Fluid is harder to move by sound waves; needs the ossicles to amplify things

Question 8

What is the attenuation reflex of the ear?

Answer 8

At the onset of loud sound, muscles attached to ossicles make their movement more rigid, diminishing sound conduction and preventing damage

Question 9

What frequencies is sound attenuation greatest at?

Answer 9

Low frequencies; not high frequencies

Question 10

Why is attenuation good for speech recognition?

Answer 10

“picks out” the high-frequencies speech out of low-frequency noise

Question 11

What happens when auditory spiral ganglion enter the brainstem?

Answer 11

Enter the brainstem via auditory-vestibular nerve; enter the medulla’s dorsal and ventral cochlear nuclei, ipsilateral to where they originated (branches to reach both), then goes through multiple parallel pathways

Question 12

What happens when cells in the ventral cochlear nucleus project their axons to the superior olive of the brainstem?

Answer 12

Axons of superior olivary neurons project to the lateral lemniscus, then to the inferior colliculus in the midbrain

Question 13

How does the dorsal cochlear nucleus’s projections to the inferior colliculus differ from the ventral cochlear nucleus’s?

Answer 13

Bypasses the superior olive

Question 14

Where do all ascending auditory pathways converge?

Answer 14

Inferior colliculus

Question 15

Where do auditory neurons in the inferior colliculus project their axons to?

Answer 15

The MGN in the temporal lobe, and then to auditory cortex

Question 16

What is different about cochlear nucleus input from the rest of the other auditory nuclei in the brain stem?

Answer 16

Cochlear nuclei receive input from ipsilateral ear only; other brain stem auditory nuclei receive input from both ears

Question 17

What is the only way brain stem damage can produce deafness in one ear only?

Answer 17

Damage to the cochlear nuclei

Question 18

Why do most spiral ganglion cells respond to sound in a limited frequency range?

Answer 18

Because they receive input from only one inner hair cell and so fire APs only when that specific portion of the basilar membrane vibrates

Question 19

What is characteristic frequency?

Answer 19

The one frequency at which an auditory neuron is most sensitive

Question 20

What are the two ways sound intensity is encoded?

Answer 20

Firing rates of neurons, number of active neurons

Question 21

What happens to the basilar membrane vibrations as sound intensity increases?

Answer 21

Greater amplitude of vibrations: causes membrane potential to be more de/hyper polarized, greater rate of AP firing; Greater distance of vibrations: activation of more hair cells, so broader frequency range for responses

Question 22

What is tonotopy?

Answer 22

Systematic organization of characteristic frequency within an auditory structure

Question 23

What part of the basilar membrane is more sensitive to high frequency vs low?

Answer 23

High at base, low at apex

Question 24

What is phase locking?

Answer 24

The consistent firing of a cell at the same phase of a sound wave; fires APs at either peaks/troughs/etc. of the wave

Question 25

What is the volley principle?

Answer 25

When intermediate sound frequencies are represented by the pooled activity of a number of neurons, each of which fires in phase-locked manner

Question 26

Why are frequencies above 4Hz represented to tonotopy alone?

Answer 26

Too fast for APs to accurately represent timing; phase locking can't occur; APs must fire at random phases

Question 27

What are the two mechanisms used to localize horizontal sound?

Answer 27

Interaural time delay and interaural intensity difference

Question 28

What causes interaural intensity difference?

Answer 28

Sound shadowing by your head

Question 29

Which stages of the auditory pathway are monaural vs binaural?

Answer 29

Only the neurons in the cochlear nuclei are monaural; everything else is binaural

Question 30

Where is the first structure that has binaural hearing?

Answer 30

Superior olive

Question 31

What is the main contributor for vertical sound localization?

Answer 31

The reflections of the pinna; angles back in due to the little nub in the ear :)

Question 32

How do neurons in the MGN reach the cortex?

Answer 32

By extending axons through the auditory radiation

Question 33

What is the laminal cell layout of the auditory cortex?

Answer 33

From Layer 1 to 6: few cells bodies -- small pyramidal -- small pyramidal -- granule -- large pyramidal-- large pyramidal

Question 34

What columns are present in auditory cortex?

Answer 34

Frequency-dominant columns

Question 35

What are isofrequency bands?

Answer 35

Run across A1, with similar characteristic frequencies

Question 36

What are the two main organizational principles of the auditory cortex?

Answer 36

Tonotopic organization; columns with similar binaural interaction

Question 37

Mammalian organs of balance/hearing evolved from what structure?

Answer 37

Lateral line organs

Question 38

How are all hair structures connected in mammals?

Answer 38

By the vestibular labyrinth!

Question 39

What are the two main structures of the non-auditory vestibular labyrinth?

Answer 39

Otolith organs and semicircular canals

Question 40

What are otolith organs?

Answer 40

Detect force of gravity, head tilt

Question 41

What are semicircular canals?

Answer 41

Sensitive to head rotation

Question 42

What are the otolith organs?

Answer 42

Saccule and utricle

Question 43

What is Scarpa's ganglion?

Answer 43

Location of cell bodies from vestibular nerve axons

Question 44

What is the otolith organ's macula?

Answer 44

Sensory epithelium, vertically oriented in the saccule, horizontally oriented in the utricle

Question 45

What are otoliths?

Answer 45

Little calcium carbonate crystals on top of the gelatinous cap of the orolith organs; exert pressure with movement, creating a force on the gelatinous cap and moving the hair bundles

Question 46

What a kinocilium?

Answer 46

In otolith organs: one especially tall cilia that cause depolarizing excitatory receptor potential when bent

Question 47

What is the ampulla?

Answer 47

Bulge in the semicircular canal; location of clusters of hair cells within a sheet of crista

Question 48

What is the cupula?

Answer 48

Gelatinous area in the middle of the ampulla

Question 49

What is the vestibulo-ocular reflex?

Answer 49

Keeps your eyes pointed in a particular direction throughout other motion; automatically instructs extraocular muscles to keep the eye in place

Question 50

What is the predominant ionic composition of perilymph?

Answer 50

Low K+, high Na+

Question 51

What is the predominant ionic composition of endolymph?

Answer 51

High K+, low Na+

Question 52

What is the endocochlear potential?

Answer 52

80 mV

Question 53

What causes the endocochlear potential?

Answer 53

Stria vascularis pumps in K+ and pumps out Na+

Question 54

What do the rods of Corti do?

Answer 54

Span the distance between basilar membrane and reticular lamina: provide structural support

Question 55

Where do hair cells synapse in the ear?

Answer 55

In neurons whose cell bodies are in the spiral ganglion in the modiolus

Question 56

What kind of neurons are spiral ganglion cells?

Answer 56

Bipolar

Question 57

How do TRPA1 channels make stereocilia very sensitive to soft sounds?

Answer 57

Connected to elastic filament tip links to adjacent cilium

Question 58

How does a tip link work?

Answer 58

When the cell is bent, the tip link is stretched/compressed, increasing or decreasing K+ influx and causing depolarization/hyperpolarization by activating Ca++ channels

Question 59

Why does K+ influx depolarize hair cells, unlike in most other cells?

Answer 59

Unusually high K+ concentration in endolymph, causing Ek to be 0, also high voltage gradient favoring it

Question 60

Which type of hair cell can share a single spiral ganglion cell?

Answer 60

Outer hair cells

Question 61

How many spiral ganglion cells does one inner hair cell feed?

Answer 61

Many!

Question 62

Why are outer hair cells cochlear amplifiers?

Answer 62

Motor proteins called proteins change the outer hair cell length; so outer hair cells respond with change in length and change in receptor potential, allowing sound signal amplification