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Anatomy (Neuro) > The Ear > Flashcards

The Ear Flashcards

1
Q

which germ layers do the external, middle, and inner ear develop from?

A

external and internal ear- ectoderm

middle ear- endoderm (outgrowth of gut tube- pharyngeal pouch)

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2
Q

the Eustachian tube of the ear connects which part of the ear to the nasopharynx (both outgrowths of gut tube/ pharyngeal pouch of endoderm)?

A

middle ear

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3
Q

which part of the ear contains the ossicles

A

middle ear- air-filled space containing malleus, incus, stapes
(these bones pinch off from pharyngeal arches that give rise to bones of lower face- mandible and hyoid)

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4
Q

which part of the ear contains vestibular labyrinth, which contains two fluid filled bags called saccule and utricle and the 3 semicircular ducts?

A

inner ear

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5
Q

where are the saccule and utricle found in the ear

A

fluid filled bags, found in vestibular labyrinth of inner ear

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6
Q

what is different about the fluid that fills both the vestibular labyrinth and the auditory labyrinth of the cochlear duct?

A

endolymph ECM has high K+ and low Na+ (opposite of normal)

bathes hair cells

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7
Q

is the endolymph of the vestibular and auditory labyrinths of the cochlear duct connected?

A

yes, through reunien duct

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8
Q

the external auditory meatus/ canal is decorated on the lateral skull by what? where does it end within the skull?

A

oracle/ pinna

ends at tympanic membrane

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9
Q

which ossicle is attached to the interior surface of the tympanic membrane

A

malleus

malleus articulates at a synovial joint with the incus, which articulates at a synovial joint with the stapes

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10
Q

what allows the ossicles in the middle ear to vibrate

A

series of synovial joints in between (malleus, to incus, to stapes)

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11
Q

which ossicle is situated at the oval window

A

stapes (in middle ear)

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12
Q

how does sound amplification occur in the middle ear

A

concentrating force per unit area that’s hitting large surface of tympanic membrane to much smaller area of the stapedial footplate (on oval window)

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13
Q

conductive hearing loss

A

problem in external or middle ear, results from interference of sound transmission
usually middle ear infections in kids, otosclerosis in adults (edges of stapedial footplate stuck to oval window)

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14
Q

otosclerosis

A

edges of stapedial footplate in middle ear stuck to oval window, results in conductive hearing loss

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15
Q

when stapedial footplate in middle ear presses against incompressible fluid of inner ear, a max displacement of the ____ occurs at the organ of Corti

A

basilar membrane

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16
Q

typical frequency range of hearing in a child? how does this change with age

A

child- 20-20,000 Hz

decreases 200-300Hz per year after 20years

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17
Q

within the coils of the cochlea in the inner ear is a tube of endolymph known as ____

A

scala media

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18
Q

the major functional component of the Organ of Corti in the inner ear

A

the basal membrane along the length of the scala media in the cochlea
home to the hair cells

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19
Q

the base of the basilar membrane (in the organ of Corti of the cochlea) is closest to ____, while its apex is closest to ____

A

basilar membrane base- close to middle ear

apex- close to coiled cochlear duct

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20
Q

compare the base and apex of the basilar membrane of the cochlea in terms of size, hair cells, and frequency

A

base- narrower/stiffer, shorter hair cells, higher frequency

apex- wider/flexible, taller hair cells, lower frequency

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21
Q

the auditory hair cells have what kind of apical specialization

A

stereocilia

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22
Q

the scala media is interposed between the scala vestibuli and the scala tympani, with both of these spaces being filled by ___

A

perilymph

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23
Q

endolymph, which bathes hair cells in the cochlea, is produced and secreted by what epithelium on the adjacent wall of the scala media?

A

stria vascularis

24
Q

the organ of Corti contains two populations of hair cells- a single row from base to apex of ____, and 3 parallel rows of ____

A

single row of inner hair cells
3 parallel rows of outer hair cells

all lying on the basilar membrane, and in a graduation of short to tall hair cells

25
Q

deflections of the stereocilia of the hair cells within the organ of Corti in which direction propagates an action potential? how is the action potential propagated?

A

deflections of stereocilia towards tallest hair cells (short –> tall) mechanically opens K+ channels, and influx (from endolymph with high K+ concentration) causes depolarization
depolarization causes Ca2+ influx at base of hair cells that causes NT release

26
Q

T/F: both inner and outer hair cells of Organ of Corti receive both afferent and efferent innervation

A

TRUE: via vestibulocochlear nerve (VIII)

afferent mainly contacts inner cells, efferent mainly contacts outer cells

27
Q

which type of hair cells are mainly responsible for initial processing and transduction of airborne sound

A

inner hair cells- 95% of afferent axons contact bases of these cells
even though there’s 3x more outer hair cells

28
Q

which hair cells are similar to muscle spindles (muscle stretch receptors) in that they contract when stimulated by efferent axons?

A

outer hair cells (in organ of corti)

29
Q

major difference in function of inner vs outer hair cells (both in organ of corti)

A

inner hair cells- sound processing

outer hair cells- amplification

30
Q

cell bodies of the vestibulocochlear nerve (VIII) are found in array of ____ ganglia positioned along the length of the cochlear duct as it spirals inside cochlea

A

cell bodies of the vestibulocochlear nerve (VIII) are found in array of SPIRAL ganglia positioned along the length of the cochlear duct as it spirals inside cochlea

31
Q

what are the two types of sensation input coming from the vestibular labyrinth and hair cells?

A

vestibular hair cells- linear acceleration (gravity)

labyrinth- angular acceleration (turn of head)

32
Q

where does sound localization processing begin?

A

rostral pons in superior olivary nuclei- compares the difference in arrival time and intensity from each ear

33
Q

after receiving input from vestibulocochlear nerve (CN VIII), the superior olivary nuclei projects to fiber bundle known as ____ to the midbrain to bilaterally activate neurons in the ____. These then use the inferior brachium to project to the ___ in the thalamus

A

CN VIII –> superior olivary nuclei (rostral pons) –> lateral lemniscus –> inferior colliculi –> inferior brachium –> medial geniculate nucleus (thalamus) –> auditory cortex

34
Q

CN VIII enters at the ____ junction of the brainstem

A

vestibulocochlear enters at pons-medulla junction

nerve fibers bifurcate upon entry to synapse on pair of cochlear nuclei- dorsal and ventral (spiral ganglion contains cell bodies of afferent cochlear nerve fibers)

35
Q

the auditory cortex receives (uni/bilateral) auditory information indirectly from (each/both) ears

A

indirect bilateral auditory info form both ears

36
Q

consequence of lesioning just one cochlear nerve/ nucleus vs any point above that in the auditory pathway

A

lesion cochlear nucleus- ipsilateral sensorineural hearing loss

lesion involving superior olive, lateral lemniscus, inferior colliculus, or higher levels- slight bilateral hearing loss because all of these process sound indirectly from both ears

37
Q

presbycusis

A

“old ear”- natural hearing loss, preferentially of higher-frequency (short) hair cells

38
Q

these otolith organs detect linear and angular acceleration in the vestibular labyrinth of the inner ear. what are?

A

saccular and utricular macula

39
Q

where is angular acceleration detected in the inner ear? and by what?

A

hair cells in the semicircular canals (of which there are 3 in each ear, all mutually perpendicular) in the vestibular labyrinth

40
Q

what is the ampulla in the inner ear?

A

enlargement situated at each end of each semicircular duct (3 in each ear) which contains hair cells positioned in the ampullary crest- stereocilia of these cells project into extracellular cupula that deflects in response to fluid displacement

41
Q

hair cells in the utricular macula are oriented ____ to sense ____ while the hair cells of the saccular macula are oriented ___ to sense ____

A

utricular macula- hair cells oriented horizontally to sense movement horizontal to plane of gravity

saccular macula- hair cells oriented vertically to sense vertical movements

42
Q

which otolith, the utricular or saccular macula, has its hair cells polarized towards the reversal line?

A

utricular hair cells polarized towards reversal line
saccular hair cells polarized away from reversal line

(stimulating stereocilia towards tallest hair cells results in depolarization- so essentially they depolarize in opposite directions–> any movement of head/body will result in some kind of depolarization)

43
Q

how does hair cell depolarization of the otolith organs compare to the hair cells in the ampullary crest?

A

otolith hair cells are polarized (utricular towards reversal line, saccular away from reversal line) so that any movement causes some kind of depolarization

all hair cells of ampullary crest polarized in same direction- means depolarization will be all or nothing

44
Q

the utricular and saccular macula (otolith organs in inner ear) project via CN VIII (vestibulocochlear) to vestibular nuclei, which activates this tract to maintain/coordinate head/ limb position relative to changes in gravity. what is this activated tract?

A

vestibulospinal tract

45
Q

lesions in the vestibulospinal tract typically do not cause weakness why?

A

vestibulospinal tract receives input from CN VIII to maintain body positions relative to change in gravity

innervates motor neurons bilaterally

46
Q

why is it important that the 3 semicircular ducts in each ear are mutually perpendicular?

A

any change in head position will stimulate hair cells in at least one of these

47
Q

what is the difference in activity of the vestibular nerves when you go from looking straight ahead to turning your head (what happens?)

A

straight ahead- no angular acceleration, resting levels of activity in pair of vestibular nerves in L/R ampullary crests

turn head horizontally- generate depolarization in side we are turning to, inhibit depolarization in side we are turning away from

48
Q

the vestibulo-ocular reflex generates conjugate eye movement that allows you to focus on object while your head moves. it uses the same tract to generate horizontal conjugate gaze- which is the (lateral/medial) longitudinal fasciculus

A

vestibulo-ocular reflex uses medial longitudinal fasciculus

also needs to use neurons in abducens and ocular motor nuclei

49
Q

if you turn your head to the right, the vestibulo-ocular reflex will cause conjugate eye movement in what direction?

A

left- vestibulo-ocular reflex helps maintain focus on object as our head turns
it’s a right side reflex though because you activate vestibulocochlear nerves on the side you turn towards (by causing hair cell depolarization)

50
Q

to maintain conjugate gaze on something while you turn your head to the right, the vestibulo-ocular reflex must move your eyes left. but neurons are activated on the side you turn towards (via depolarization in semicircular canals). how does this work then?

A 
turn to right: right vestibulocochlear (CN VIII) sends axons across midline to LEFT abducens (look lateral) nucleus next to caudal pons.
heavily myelinated (read: fast) medial longitudinal fasciculus leave abducens, cross midline and up to midbrain to get to CN III (oculomotor)

(reminder: this is same fast pathway of horizontal conjugate gaze, because that’s pretty much what you’re doing)

51
Q

vertigo is abnormal perception of rotation/motion. given this, someone with vertigo might have a lesion where?

A

vestibular nerve/ nuclei (of vestibulocochlear nerve, CN VIII)
vertigo is worse in peripheral lesions than central lesions

52
Q

Meniere’s disease and cause

A

circulation problem of endolymph, causes abrupt vertigo attacks and sometimes tinnitus and ipsilateral sensorineural hearing loss (if cochlea hair cells involved)
occurs from distension of endolymph-filled spaces in cochlear and vestibular prats of labyrinth

53
Q

vestibular-evoked nystagmus

A

nystagmus- slow, rhythmic oscillation of eye to one side followed by fast corrective reflex in opposite direction (usually horizontal)- so reflex is away from side of lesion

can occur form lesion in labyrinth, vestibular nerve/nuclei (among other causes)

54
Q

the fast reflex of vestibular-evoked nystagmus is towards or away side of lesion?

A

away from side of lesion

direction of nystagmus defined by direction of fast reflex because it’s easier to see

55
Q

how does the caloric test evaluate vestibular ocular relfex?

A

put cold water in external auditory meatus- works like an inhibitor (mimics lesion), should see slow drift of eyes towards the ear followed by fast reflex away (like vestibular-evoked nystagmus)
warm water- stimulates, so eye drift will be away from ear followed by fast reflex towards ear

COWS: cool, opposite/ warm, same

Anatomy (Neuro) (13 decks)

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