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NE Exam 3 > Physiology Of The Auditory System > Flashcards

Physiology Of The Auditory System Flashcards

1
Q

Describe the basilar membrane near the oval/round windows (the base)

A

Fibers near the oval/round winds are narrow and stiff
Higher frequency sounds cause greater deflection at this location (at its base)
Ex. Bird singing, whistle

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2
Q

Describe the basilar membrane at its apex (near the helicotrema)

A

Fibers are wider and more flexible
Lower frequency sounds produce greater deflection in this region where the membrane is loose and flexible
Ex. Thunder, tuba

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3
Q

The frequency of sound (pitch) is coded by what?

A

Where along the basilar membrane there is the greatest deflection

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4
Q

Describe hair cells

A

Receive afferent and efferent input but are not neuronal
Are mechanoreceptors (covert mechanical signal into electrical signals)
Polarized epithelial cells
Have basal and apical ends
Stiff, graded in size and rich in actin

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5
Q

What exists on the apical surface of a hair cell?

A

Stereocilia

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6
Q

What exists on the basal side of the hair cell?

A

Neural synapses

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7
Q

What is endolymph?

A

The K+ rich fluid filling the cochlear duct and the membranous labyrinth
Bathes the apical end of the hair cells
Similar to ICF (high in K and low in Na)
Found in scala media and produced by stria vascularis

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8
Q

What is perilymph?

A

The K+ poor fluid that bathes the basal end of the cochlear hair cells
Similar to ECF (high in Na and low in K)
Found in scala vestibuli and scala tympani

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9
Q

What is the role of stereocilia during sound transmission?

A

Following deflection of the stereocilia toward the tall stereocilia, K ions enter the hair cell and depolarize it
Depolarization occurs when cation channels open at the apex of the stereocilia
Release of NT (glutamate) and generation of APs occur in the 8th CN fibers

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10
Q

What connects stereocilia in a hair cell?

A

Connected to each other via tip links that transmit force to an elastic gating spring (protein bridge) which in turn opens the TRPA1 channels
Even small vibrations of 0.3nm (size of an atom) can cause channel opening

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11
Q

What occurs if stereocilia deflection in the direction opposite of the tallest one?

A

Hyperpolarization of the hair cell
Occurs bc K channels close -> no positive charge flow into the cell -> TRPA1 closes and Ca doesnt flow into the cell -> no release of NT -> no activity in the afferent neuron -> no sound is heard

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12
Q

What is the stria vascularis?

A

A highly vascularized area located in the lateral wall of the cochlear duct (scala media)
Maintains electrochemical properties of the endolymph (by keeping it concentrated with K+)
A common source of ototoxic drug secretion into the cochlea (crosses the BLB)

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13
Q

What is the blood-labyrinth barrier (BLB)?

A

The high endocochlear potential of +80mV maintained by the stria vascularis drives positively charged ions into the hair cell down their concentration gradient
This forms the BLB which is one of the main sites of drug entry to access the inner hair cells (sometimes to its detriment)

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14
Q

Any substance (medication, CO, drugs, etc) that disrupts the function of the stria vascularis will do what?

A

Dismiss the endocochlear potential of the endolymph and thus impact hearing

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15
Q

What is the primary function of inner hair cells?

A

Primary source of auditory information

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16
Q

What is the primary function of outer hair cells?

A

Amplify sound waves
Also contractile which makes them a specialized type of epithelial cell
Their contractile properties boost the mechanical vibrations of the basilar membrane which makes them act like an amplifier

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17
Q

How are inner hair cells arranged?

A

In a single layer

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18
Q

How are outer hair cells arranged?

A

Arranged into three rows

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19
Q

What do inner hair cells synapse with?

A

Synapse with the peripheral terminal of a primary afferent sensory neuron

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20
Q

What do outer hair cells synapse with?

A

Also form a synapse with sensory afferent peripheral terminals from the spiral ganglion

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21
Q

What is the efferent activity of inner hair cells?

A

An efferent neuron modulates activity

22
Q

What is the efferent activity of an outer hair cell?

A

Also form a synapse with terminals from efferent neurons

23
Q

What are the olivocochlear efferents that are associated with outer hair cells?

A

Bc the motility of the outer hair cells cause the basilar membrane to move it is conceivable that this movement could be retrograde/backward toward the oval window and through the middle ear via the ossicles to cause displacement of the TM
This process would result in the ear itself producing sound
Impulses originate in the superior olivary complex (hence the name)

24
Q

What innervates inner hair cells?

A

Lateral olivary complex neurons

25
Q

What are outer hair cells innervated by?

A

Medial olivary complex neurons

26
Q

What are otoacoustic emissions (OAE)?

A 
The sounds that the ear produces itself can be measured in the EAM as otoacoustic emissions 
Such measurements are routinely done in infants to assess the function of the inner and middle ears 
Usually inaudible (low intensity) 
Clinical importance: newborn screenings, tinnitus and ototoxicity
27
Q

What are the two types of otoacoustic emissions?

A
  1. Spontaneous: occurs in 1/3 of normal people, usually pure tones or clicks and probably generated from the motile outer hair cells
  2. Evoked emissions are used to test for hearing loss (no emissions evoked if damage present)
28
Q

What is the pathway for auditory processing?

A

Cochlear nuclei -> superior olivary complex -> inferior colliculus -> medial geniculate nucleus -> auditory cortices

29
Q

The central portion of the cochlear nerve branches to reach what?

A

The cochlear nuclear complex which comprises of the ventral and dorsal cochlear nuclei

30
Q

What is the function of the dorsal (posterior) cochlear nuclei?

A

Integrates the acoustic information with somatosensory information

31
Q

What is the function of ventral (anterior) cochlear nuclei?

A

Begins processing the temporal and spectral features of sound
(Nature of the sound - high, low)

32
Q

Describe the superior olivary complex

A

First site in the brainstem where info from both ears converges
This binaural processing is essential to accurately localize sound
Receives excitatory input from glutamate/aspartate
Includes the medial and lateral superior olivary nucleus

33
Q

What is the function of the medial superior olivary nucleus (MSO)?

A

Generates a map of the interaural time differences which helps localize the location of sound
(Localizes sound due to differences in time of arrival to ears)

34
Q

What is the function of the lateral superior olivary nucleus (LSO)?

A

Generates a map of the interaural intensity differences which help localize the source of sound
(Localizes sound due to differences in intensity of sounds b/w ears)

35
Q

What is the function of the inferior colliculus?

A

Suppresses information related to echoes which would interfere with localization and arrives at a final estimation of localization of sound along the horizon
Info about time and intensity differences converge into the IC that together with echo suppression helps crate a precise origin of sound location

36
Q

What is the function of the medial geniculate nucleus?

A

Relay station in the auditory pathway
Lots of convergence from distinct spectral and temporal pathways allowing for processing features of speech inflections
Precise info regarding intensity, frequency and binaural properties of sound are integrated and relayed onward

37
Q

What is the function of the primary auditory cortex?

A

Essential in conscious perception of sound
Higher order processing of sound (loudness, modulations in volume, rate of frequency modulation)
More rostral areas are activated by low frequencies and more caudal areas respond to higher frequencies

38
Q

What is the function of the auditory (secondary) association cortex?

A

Composed of multiple areas (Broca’s, Wernicke’s, etc)
Less specifically organized in the tonotopic arrangement than the primary auditory cortex
Thought to respond to more complex sounds like musics, ID (naming) a sound, and speech

39
Q

What are the three types of efferent input to the auditory system?

A

Olivocochlear efferents, middle ear muscle motoneurons, autonomic innervation of the inner ear (comprised of sympathetic adrenergic fibers)

40
Q

Describe olivocochlear efferents

A

Originate in the superior olivary complex
Describes basilar membrane motion
Reduces responses of inner hair cells and auditory nerve fibers + reduces response to (loud) noises
May protect hair cells from damage due to intense sounds

41
Q

Describe middle ear muscle motoneurons

A

Includes motor innervation to the tensor tympani to the malleus and TM + the stapedius to the stapes
Bilateral response to high sound levels
Act at low frequencies
May prevent damage, low frequency masking (improving speech discrimination) and hair cells from damage due to intense sounds
Implicated in tinnitus

42
Q

Autonomic efferent innervation of the inner ear may arise from what?

A

CN VIII
Caroticotympanic nerve off superior cervical ganglion: innervates the mucous glands of the tympanum and the blood vessels of the TM + all its contents
Acoustic nerve supplies blood vessel sympathetics - regulates vascular tone in blood supply to the cochlea

43
Q

What is sensorineural hearing loss?

A

Caused by damage to hair cells, nerve fibers or both
Noise damage, ototoxic drugs, age related, loss of unknown etiology
Some hearing may be restored with a cochlear prosthesis

44
Q

Are inner or outer hair cells more susceptible to damage?

A

Outer hair cells

45
Q

Injury to outer hair cells causes what?

A

Decrease in sensitivity (higher thresholds) and broader tuning

46
Q

Injury to inner hair cells causes what?

A

Cuts off auditory inputs to the CNS

47
Q

Which area of the basilar membrane/cochlea is more susceptible to injury?

A

The base (high frequency) end of the cochlea is more susceptible than the apical (lower frequency) end

48
Q

What is the anterior semicircular canal activated by?

A

Rotation in the vertical plane forwards maximally

Ex. Tripping while walking

49
Q

What activates the horizontal semicircular canal?

A

Rotation in the horizontal plane

Ex. Twirling on ice skates

50
Q

What activates the posterior semicircular canal?

A

Rotation in the vertical plane backwards

Ex. Falling backwards like during a trust exercise

51
Q

What does the utricle detect?

A

Linear acceleration forward and backward

Ex. Running

52
Q

What does the saccule detect?

A

Linear acceleration up and down

Ex. Slam dunking a basketball

NE Exam 3 (16 decks)

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