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Neurobiology II > Vestibular and Auditory System > Flashcards

Vestibular and Auditory System Flashcards

1
Q

Anatomy of the outer ear.

A

Pinna (external ear)
Auditory canal, ends at the tympanic membrane
Tympanic membrane: boundary between outer and middle ear

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2
Q

Anatomy of the middle ear.

A

Ossicles: malleus, incus, and stapes

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3
Q

Anatomy of the inner ear.

A

Cochlea
Labyrinth
Vestibule: utricle and saccule

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4
Q

Function of the auricle and auditory canal.

A

Direct sound inward toward the tympanic membrane. The auricle filters the sound waves as it directs them into the auditory canal.

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5
Q

When the sound waves press on the tympanic membrane, what occurs afterward?

A

It will move the malleus first, which will then move the incus, which will then move the stapes.

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6
Q

The stapes is attached to what structure?

A

Attached to cochlear entrance at oval window.

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7
Q

The vibration of the ossicles does what?

A

Amplifies sound waves by the stapes pushing in and out of the oval window, causing the vibrations to reach the inner ear.

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8
Q

The middle ear contains what two muscles? What are their functions?

A

Tensor tampani muscle: dampens movements of malleus.
Stapedius muscle: dampens movements of stapes.

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9
Q

What three structures are also part of the cochlea?

A

Cochlear duct in the center
Vestibular duct and tympanic duct
Semicircular canals

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10
Q

Describe the cochlear duct.

A

It is a spiral organ (organ of Corti) with an area of thick epithelium. It contains hair cells within the spiral organ with stereocilia projecting into the tectorial membrane.

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11
Q

Describe the row of inner hair cells of the cochlea.

A

One row of inner hair cells along the central rim of the cochlea. They are responsible for sound transduction; higher-frequency sounds activate hair cells near the oval window and lower frequency sounds activate hair cells near apex of the cochlea. Excitatory synapses on terminals of primary sensory neurons (cell bodies in spiral ganglion).

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12
Q

Describe the row of outer hair cells of the cochlea.

A

Three rows of outer hair cells, they modulate stiffness of the tectorial membrane and emit sound. These hair cells are more modulatory and do motor function.

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13
Q

How does the transmission of vibration go from the oval window to the cochlea?

A

The vibrations will go through the vestibular duct to the tympanic duct via movement of endolymph. This will generate movement of the basilar membrane and hair cells within the cochlear duct.

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14
Q

Since the stereocilia are rigid within the tectorial membrane, what will occur if they are displaced?

A

The displacement will cause a sheering force between the stereocilia and their respective hair cell. The sheering activates the hair cell, inducing transduction of vibration to a neural impulse.

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15
Q

The primary sensory neurons are found where? They send axons to what? Then that nerve goes to where?

A

They are housed within the spiral ganglion where they send axons to the cochlear division of CN VIII; CN VIII will then synapse with dorsal and ventral cochlear nuclei.

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16
Q

Hearing pathways ascend through the brainstem bilaterally to…

A

Inferior colliculi (midbrain)
Medial geniculate nuclei (nucleus)
Auditory cortex (cerebrum)

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17
Q

Describe the pathway of the dorsal cochlear nucleus.

A

The fibers ascend in the contralateral lateral lemniscus within the auditory pathway. They are within the pons and lower midbrain where they project dorsally to the inferior cerebellar peduncle and cross at the pontine tegmentum. The fibers will then terminate within the inferior colliculus.

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18
Q

Describe the pathway of the ventral cochlear nucleus.

A

Fibers project ventrally to the inferior cerebellar peduncles to synapse BILATERALLY in the superior olivary nuclear complex of the pons. The fibers cross from trapezoid body (white matter). They then ascend bilaterally in lateral lemniscus to reach inferior colliculi.

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19
Q

The ventral cochlear nucleus synapses bilaterally at the superior olivary nucleus because…

A

It has to localize sounds horizontally in space.

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20
Q

From the inferior colliculus, the auditory pathway projects to…

A

Medial geniculate nuclei of the thalamus, project in auditory radiations to the primary auditory cortex.

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21
Q

Job of the efferent pathways (there are 2).

A

Modulate sensitivity of hair cells in response to sounds of varying intensities. Or, they can go through the reflexive pathway that goes from the ventral cochlear nuclei to the facial and trigeminal motor nuclei to contract stapedius and tensor tympani muscles to dampen the response of middle ear to loud sounds.

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22
Q

Three overarching functions of the vestibular system.

A

Adjustment of posture, muscle tone, and eye position in response to movement/head in space.

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23
Q

Name the structures from the vestibular system that is correlated with the function:
Sensory input
Central processor
Motor output

A

Sensory input: vestibular, somatosensation, vision
Central processor: cerebellum, vestibular nuclei
Motor output: postural reflexes, eye movement

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24
Q

Describe the bony vs membranous labyrinth.

A

Bony: compact bone filled with perilymphatic fluid (similar to CSF); it communicates via cochlear aqueduct with CSF.
Membranous: suspended within bony labyrinth by perilymphatic fluid and supportive connective tissue; it is filled with endolymphatic fluid (similar to intracellular fluid).

25
Q

True or False: under normal circumstances, the perilymph and endolymph directly communicate with each other.

A

False!

26
Q

The semicircular canals detect which type of acceleration?

A

Angular acceleration in 3 axes.

27
Q

Describe the structure of the semicircular canals.

A

There are 3 canals: anterior, posterior, and horizontal; each canal is paired with a canal on the opposite side. The canals also have an ampulla, a widened end of one side of the semicircular canal.

28
Q

Further describe the ampulla, found within the semicircular canals.

A

It contains a gelatinous cupula, which is a flexible membrane; the cupula also contains mechanoreceptors that are going to be responsible for detecting angular acceleration. There is also a crista ampullaris which contains a tuft of blood vessels, nerve fibers, and supporting tissue. Hair cells rest on the crista ampullaris and are embedded within the cupula.

29
Q

Otoliths detect which type of acceleration?

A

Linear acceleration and head tilt, specifically how gravity acts on the head.

30
Q

What are the otolith organs?

A

Saccule and utricle

31
Q

What do otoliths contain that resemble the crista ampullaris found in the semicircular canals?

A

Maculae

32
Q

Maculae, which are found within the otoliths, contain what? Where do they sit?

A

Contain otoconia, calcium carbonate crystals within otolith membrane, which sit on gelatinous layer.

33
Q

Hair cells of the otoliths are embedded within?

A

Within the gelatinous layer: medial wall of the saccule and floor of utricle.

34
Q

In terms of an x and y-axis, the medial wall of the saccule will detect which axis of gravity? Floor of utricle?

A

Medial wall of saccule will detect the y-axis, and the floor of the utricle will detect the x-axis.

35
Q

Hair cells of the semicircular canals and otoliths convert the _____ energy generated by _____ motion into _____ _______ directed to specific areas of brainstem and cerebellum.

A

Mechanical
Head
Neural discharges

36
Q

What does push-pull-change mean regarding the semicircular canals?

A

With head rotation, perilymph moves in the same direction as angular movement, and endolymph moves in the opposite direction, displacing hair cells in cupula. The displacement of the hair cells activate terminals of bipolar primary sensory neurons, sending axons to cell bodies in vestibular ganglia of Scarpa.

37
Q

With movement, hair cells of the semicircular canals will be bent towards or away from the longest process of hair cell. When it is bent away, will we see inhibition or excitation occur? What if it is bent towards?

A

Bent away will cause inhibition and bent towards will cause excitation.

38
Q

If you turn your head to the left, you stimulate both horizontal semicircular canals, but the left will be _______ while the right is ________.

A

The left will be excitatory while the right is inhibitory.

39
Q

The otolith membrane has more mass than the cupula, so this causes increased sensitivity to…

A

Gravity and linear acceleration.

40
Q

With head tilt or acceleration, gravity/other acceleration pulls on the crystals in the otoliths. This will activate hair cells and cause?

A

Some hair cells to be maximally excited and some to be maximally inhibited.

41
Q

The superior vestibular ganglion receives input from? The inferior vestibular ganglion?

A

Superior: utricle, anterior saccule, anterior and lateral semicircular canals.
Inferior: posterior saccule and posterior semicircular canals.

42
Q

Describe the 4 major nuclei of the vestibular nuclei.

A

Superior: relay for VOR
Medial: largest of the nuclei; relay for VOR; vestibulospinal reflexes.
Lateral: principal nucleus for vestibulospinal reflex.
Descending: connected to all nuclei and cerebellum.

43
Q

Medial longitudinal fasciculus
Nucleus of origin
Projection
Function

A

Nucleus of origin: medial vestibular nucleus and superior vestibular nucleus.
Projection: ascends to motor nuclei of extrinsic muscles of the eye (III, IV, VI).
Function: vestibulo-occular reflex (VOR) - adjust eyes in response to head movements.

44
Q

Role of the cerebellum in vestibular connections/pathways.

A

It modulates vestibular reflexes; the flocculus adjusts/maintains gains of VOR; the nodulus adjusts duration of VOR and processes otolith information; anterior-superior vermis is involved with the vestibulo-spinal reflex.

45
Q

Cortex in the connections/pathways of vestibular nuclei:
Projects to
Function

A

Projects to ventral posterior nucleus of thalamus, which goes to the thalamus.
Functions to control neck and head position.

46
Q

What do each of the reflexes help to do:
VOR
VSR
VCR

A

VOR: stable vision during head motion
VSR: stable body during head motion
VCR: stable neck during head motion

47
Q

What is the pathway of relays with the VOR?

A

Vestibular nuclei to the ipsilateral abducens to the contralateral oculomotor nucleus.

48
Q

The peripheral system receives vascular supply from? The central system receives vascular supply from?

A

Peripheral: labyrinthine artery (branch of AICA) - common cochlear artery and anterior vestibular artery.
Central: PICA, basilar artery, and AICA

49
Q

Unilateral hearing loss can occur from damage to what structures?

A

External auditory canal, middle ear, cochlea, CN VIII, and cochlear nuclei.

50
Q

Conductive hearing loss can occur from damage to what structures?

A

Abnormalities of external auditory canal or middle hear.

51
Q

Sensorineural hearing loss can occur from damage to what structures?

A

Cochlea or CN VIII.

52
Q

Acoustic neuroma develops where? Signs/symptoms include?

A

Develops where C VIII enters internal acoustic meatus. A pt can have unilateral hearing loss, tinnitus (ringing in ear), and unsteadiness.

53
Q

Vertigo

A

True dizziness; spinning sensation of movement or room spinning.

54
Q

Most common causes of vertigo

A

Peripheral structures

55
Q

What are the three peripheral disorders?

A

Benign paroxysmal positional vertigo: brief episodes of vertigo lasting a few seconds and can occur with position changes.
Vestibular neuritis
Meniere’s disease

56
Q

Central vestibular disorders

A

Brainstem stroke or posterior fossa hemorrhage
MS

57
Q

Nystagmus occurring due to a peripheral lesion (inner ear).

A

The onset of symptoms are delayed, habituation does occur; horizontal or rotatory, not vertical; does NOT change directions; prominent nystagmus ONLY if vertigo is present as well.

58
Q

Nystagmus occurring due to a central lesions (brainstem or cerebellum).

A

The onset of symptoms are immediate or delayed, habituation does not occur; horizontal, rotatory, or vertical; may change directions; prominent nystagmus may occur in the absence of vertigo.

Neurobiology II (4 decks)

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