Lectures 20-22: Auditory System Flashcards Preview

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Flashcards in Lectures 20-22: Auditory System Deck (78):
1

Audible range in Hz and dB. What frequency are we most sensitive?

20 - 20,000 Hz (1,000 - 3,000 we are most sensitive) and 1 - 120 dB

2

External ear: parts and functions

Pinna (reflects low frequencies for vertical sound localization) and external auditory meatus (magnifies 3,000 Hz sound by passive resonance)

3

Middle ear: parts

Ossicles (malleus, incus, stapes), muscles (tensor tympani, stapedius), eustachian tube

4

Where does the stapes foot plate insert?

Oval window

5

Tensor tympani muscle innervation and function. What bone does it attach to?

Innervated by CNV, improves transmission of high frequencies; malleus

6

Stapedius muscle innervation and function

Innervated by CNVII, stiffens chain of ossicles to dampen sound (stapedius reflex)

7

Cochlea: parts, fluid, and function. Describe why one of the fluids is special.

Bony cochlea (filled with perilymph) and membranous cochlea (filled with viscous endolymph [high K+, low Na+])

8

Three cochlear compartments

Scala vestibuli (in), scala media (membranous), scala tympani (out)

9

How is sound transmitted?

Stapes oscillates, pressure wave transmitted through oval window --> scala vestibuli --> scala tympani (base to apex) --> round window

10

Where does hearing happen? Two membranes flanking scala media? Third membrane? Where are the hair cells?

Scala media; vestibular and basilar membrane; tectorial membrane; sit on basilar membrane and extend to tectorial membrane

11

Organ of Corti consists of...

Basilar membrane, inner and outer hair cells, tectorial membrane

12

Stria vascularis

Highly vascular structure that produces endolymph on lateral wall of Organ of Corti

13

Inner hair cells

Single row, responsible for hearing, 95% of input to auditory nerve

14

Outer hair cells

Three rows, critical for audition: input from superior olive, sharpen sound frequency resolution, protect hair cells from loud noise, otoacoustic emissions

15

Hair cells "hairs"

Sterocilia (arranged like staircase) and kinocilium (taller)

16

Deflection toward kinocilium

Depolarization of hair cell membrane --> exocytosis --> excites distal process of auditory nerve

17

Deflection away from kinocilium

Hyperpolarization of hair cell membrane --> less signal --> inhibits

18

Basilar membrane is wider and more flexible at the _______ for which kind of tones? And the converse? What is this called?

Apex = low tones; narrower and more rigid at base = high tones; tonotopic organization of basilar membrane

19

What is a special function of the outer hair cells? What are they vulnerable to?

Amplify movement of basilar membrane in response to low intensity sounds; vulnerable to aminoglycoside antibiotics (ototoxic)

20

Steps of hearing after hair cells

1. Inner hair cells activate distal process of auditory nerve; 2. Cell bodies of auditory nerve fibers are located in Spiral Ganglion; 3. Proximal processes of auditory nerve enter brainstem and pontine-medullary junction

21

Projection pathway of auditory system

Cochlear nuclei (located lateral to inferior cerebellar peduncle) --> superior olive (some crossing here) --> inferior colliculus --> medial geniculate body (thalamus) --> auditory cortex

22

Superior olive is responsible for...how? Fibers from here ascend in what tract? What other fiber tract projects from here?

Horizontal localization of sound because it receives binaural input from cochlear nuclei; calculate interaural intensity (loudness) and timing differences; lateral lemniscus; also sends a projection back to outer hair cells via olivocochlear bundle

23

Input from olivocochlear bundle does what? (2)

Selective auditory attention when there is background noise, protection from loud noise

24

Where do we find the medial geniculate nuclei?

Hanging off the thalamus at the level of the midbrain

25

Were does the medial geniculate nucleus project?

NOT through internal capsule, but sneak behind posterior limb of IC through the auditory radiation and synapse at Heschl's gyri

26

Describe Heschl's gyri tonotopic organization

Anterior --> low, Posterior --> high frequency (corresponding apex --> base)

27

What else does the auditory cortex convey?

What and where sound information

28

Newborn hearing test looks for (2)

Otoacoustic emissions (haircell dance) and auditory brainstem responses

29

What two important pieces of information are conveyed by the peripheral vestibular system?

1. Angular acceleration of the head; 2. Linear acceleration of the head (up and down)

30

Vestibulo-thalamo-cortical pathway does what? What thalamic nucleus? To where in cortex?

Conscious perception of equilibrium; VP nucleus (contralateral); posterior parietal cortex (primary vestibular cortex)

31

Vestibulo-ocular reflex (VOR). Afferent and efferent limb?

Steady gaze during head movement; afferent limb = vestibular, efferent limb = oculomotor

32

Vestibulo-spinal tracts: what two functions and what are their pathways? Ipsi/bilateral?

Postural equilibrium: lateral tract, sends input down spinal cord to innervate motor neurons to extensor musculature (ipsilateral); head stability during body movement: medial tract (vestibulo-colic pathway) maintains head stability during body movement through MLF to cervical spinal cord (bilateral)

33

Vestibulo-autonomic reflex. Test? Describe.

Effects compensatory changes in BP, respiration and digestion with changes in posture; tilt table test, normal = increased BP when table titled 70 degrees vertically, orthostatic hypotension is a drop in BP when table is tilted

34

Components of peripheral sensory apparatus (labyrinth)

Semicircular canals, otolith organs

35

Components of the central pathways of the vestibular system

Four vestibular nuclei; projections to the thalamus, oculomotor neurons, spinal cord, brainstem; reciprocal connections with cerebellum

36

Semicircular canals: function and names

Detect angular head acceleration; anterior/superior, posterior/inferior, lateral/horizontal

37

Otolith organs: function and components

Detect linear acceleration of the head; utricle and saccule

38

Similar to the auditory system, the bony cavities of the vestibular system and filled with _________, while the membranous sacs are filled with __________

Perilymph, endolymph

39

Swelling at semicircular canals called. What is inside this? What is this made of?

Ampulla; Crista ampullaris = receptor sheet for semicircular canals; hair cells! with the same excitation/inhibition pattern as auditory system

40

What are hair cells sensitive to? (3)

Trauma, aminoglycoside toxicity, and aging

41

What is different about the hair cells in the semicircular canals, as compared to the those in the cochlea?

Lodged in the gelatinous cupula (not tectorial membrane)

42

Clinicians have defined how many planes of movement for the canals? Describe

Three: horizontal, RALP, LARP

43

Saccule detects...

Linear acceleration/displacement in vertical plane

44

Utricle detects...

Linear acceleration in horizontal plane

45

Sensory sheets in otolith organs are called...hairs protrude into...comprised of?

Macula; otolithic membrane; gelatinous structure and otoconia (calcium carbonate crystals)

46

How is tilt detected in otolithic membrane?

Shifting heaviness of otoconia

47

Hair cells of the vestibular system synapse on...cell bodies where? Synapses where? How many?

Distal processes of VIII; Scarpa's Ganglion; vestibular nuclei (4)

48

Vestibulo-colic reflex does what?

Maintains head stability during body movement (keeps head upright)

49

Vestibular evoked myogenic potentials (VEMPS) tests what? Describe.

Tests otolith function. Apply sound to patient --> vestibular nuclei --> medial/lateral vestibulospinal tract --> record myogenic potential on neck attributable to sound.

50

Two types of hearing loss and regions of the ear they affect

Conductive loss (outer --> middle ear) and sensorineural hearing loss (SNHL; inner ear --> CNS)

51

Weber test assesses which type of hearing loss? How? What if they have SNHL?

Conductive: sound lateralizes to ear with conductive hearing loss; lateralizes AWAY from SNHL

52

If someone has SNHL, what will happen in the Rinne test? What if they have conductive hearing loss?

SNHL = normal test, air louder than bone; Conductive = positive test, bone louder than air

53

What does an audiogram assess? (3)

Pure tone threshold for air and bone, and speech reception, speech discrimination

54

What does tympanometry assess?

Movement of ear drum: assesses middle ear pressure

55

How do you screen hearing in newborns? What's the next test?

Otoacoustic emissions; auditory brainstem response

56

Causes of conductive hearing loss (6)

Cerumen, eustachian tube swelling, tympanic membrane perforation, excess fluid, cholesteatoma, or an ossicular abnormality

57

Name and describe an ossicular abnormality and treatment

Otosclerosis: fixation of stapes bone; staepectomy

58

Causes of sensorineural hearing loss (6)

Noise, age, genetics, toxins, virus and acoustic neuroma

59

T/F: SNHL is usually bilateral

True! (except for Meniere's or acoustic neuroma)

60

Hearing loss of age

Presbycusis

61

What is an acoustic neuroma?

Benign tumor of the schwann cells of the vestsibulochoclear nerve

62

Who would get a cochlear implant?

Severe bilateral SNHL in an adult or child who has had no benefit from hearing aid

63

Four-step approach to the dizzy patient

1. Understand vestibular physiology; 2. Classify the complaint using history; 3. Peripheral (ENT, labyrinth) or central (neurological); 4. Know the common vestibular syndromes

64

Classifying dizziness and common causes (3)

1. Vertigo = false sense of motion (vestibular); 2. Imbalance/disequilibrium (vestibular, visual, proprioceptive, CNS [cerebellar, etc.]); 3. Lightheadedness (cardiovascular/metabolic)

65

What test measures eye movement?

VNG Videonystagmography

66

In a peripheral vestibular lesion, nystagmus is seen away/toward lesion

Away

67

Five common vestibular syndromes

Acute, unilateral vestibular loss, Meniere, BPPV, bilateral vestibular loss, migraine-associated dizziness

68

Acute unilateral vestibular loss presents with (4)...prognosis? Common causes (4)

Sudden onset of vertigo, N/V, nystagmus, Romberg; good; infection, neuroma, injury, infarction

69

Meniere's syndrome presents with...

Episodic vertigo, N/V, unilateral hearing loss (w/ tinnitus)

70

What is the pathophysiology of benign positional paroxysmal vertigo (BPPV) and what does this cause? Treatment?

Dislodging of otoconia; acute vertigo brought on by positional change and rotary nystagmus elicited by Dix-Hallpike maneuver; particle repositioning

71

Four common causes of central vertigo

Cerebellopontine angle tumor, stroke, migraine, MS

72

T/F: Hearing loss is common with central vertigo

False!

73

In central vertigo, nystagmus is/is not inhibited by fixation of eyes onto an object

NOT

74

Bilateral vestibular loss can be caused centrally/peripherally/both

Both

75

What are some causes of bilateral vestibular loss (5)? Symptoms? Prognosis?

Aminoglycoside or other toxicity, age related factors, infections, trauma, inflammatory/autoimmune conditions; ataxia + oscillopsia (the illusion that the environment is moving when we move our heads) but NO VERTIGO; prognosis = poor

76

In bilateral vestibular vertigo, what happens with caloric response?

Absent in both ears

77

Unilateral deafness must be due to damage to what structures. Why?

Ear, auditory nerve, or cochlear nuclei (nothing higher); after the nuclei, all tracts carry bilateral information

78

All five functional pathways of the vestibular system are under control of this structure.

The cerebellum

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