Vestibular and Auditory Systems

Question 1

Perilymph

Answer 1

Outside the labyrinth and in 2 canals of the cochlea
Fills the space between bony and membranous labyrinths
Composition similar to extracellular fluid and CSF (low K, high Na)
Ultrafiltrate of CSF or blood
Drains via venules and middle ear mucosa

Question 2

Endolymph

Answer 2

In the lumen of the semicircular canals, utricles, and saccules
Unique fluid similar to intracellular fluid (high K and low Na)
Produced by the dark cells of the sensory epithelium
Absorbed by the endolymphatic sac

Question 3

Vestibular system function

Answer 3

Detects body position relative to gravity and the motion of body in space
Equilibirum (balance and postural stability)
Motor output (reflex and controlled)
Vision (control of head and eye motion and stabilizing visual gaze)

Question 4

Semicircular canals detect…

Answer 4

Angular acceleration (= head rotations)
Each of the 3 canals is sensitive to head rotations in the plane of that canal
Together they can specify the direction and amplitude of any head rotation

Question 5

Otolithic organs (utricle and saccule) function

Answer 5

Sense body orientation and linear motion
Utricle: horizontal
Saccular: vertical

Question 6

Ductus reuniens

Answer 6

Connects the utricle and saccule to the cochlea

Question 7

Hair cells

Answer 7

Excitatory neurons that release glutamate
In the cochlea, utricle, saccule and semicircular canals
Each cell has several cilia projecting from its apical pole
Base of cell is surrounded by receptive terminals of CN 8

Question 8

Orientation of stereocilia on hair cells

Answer 8

Oriented in rows of ascending height
Tallest is nect to the single kinocilium
Cilia are linked together by filaments

Question 9

What happens to the hair cell when the stereocilia are bent

1. Towards to kinocilium
2. Away from the kinocilium

Answer 9

1. Depolarized

2. Hyperpolarized

Question 10

Parts of the semicircular canals

Answer 10

Ampulla (swellings at the ends)
Cristae (hair cell sensory epithelium in the ampulla)
Cupula (acellular, gelatinous mass

Question 11

What structures control the position of the eyes during the vestibulo-ocular reflex?

Answer 11

Semicircular canals

Question 12

Parts of the utricle and saccule

Answer 12

Contain a macula (= to crista of canals, so contain hair cells)
Hair cells project into the otolith membrane
Membrane contains the otoconia (rocks)
Respond to gravity and linear acceleration

Question 13

Main role of utricle and saccule

Answer 13

Cause reflex adjustments (head position via neck and trunk muscles, body position via limb muscles)

Question 14

4 vestibular nuclei (where from, what to)

Answer 14

Superior (from canals to MLF for eye movement coordination)
Medial (from utricle and saccule to neck and trunk)
Lateral (from U and S to limbs)
Inferior (receives input from all components and projects to cerebellum which coordinates all motor activities and modulates VOR)

Question 15

Benign Paroxysmal Positional Vertigo

Answer 15

Displaced otoconia lodged in the semicircular canals

Question 16

Meniere’s Disease (endolymphatic hydrops)

Answer 16

Increased endolymph in inner ear

Question 17

Vestibular neuritis

Answer 17

Viral infection of the vestibulo-cochlear nerve

Question 18

Perilymph fistula

Answer 18

Breach in the oval and/or round window

Question 19

Ototoxicity

Answer 19

Toxicity induced death of hair cells

Question 20

Mal de Debarquement

Answer 20

Failure of CNS plasticity to respond to prolonged movement

Like not being able to adjust after having sea legs

Question 21

How does aging impact the vestibular system?

Answer 21

Gradual loss of hair cells

Normally compensated by vision, but can be a problem in the dark or with eyes closed

Question 22

Is bilateral or unilateral vestibular dysfunction more severe?

Answer 22

Unilateral

Question 23

What does
1. Frequency
2. Amplitude
translate to?

Answer 23

1. Pitch

2. Loudness

Question 24

Auricle/Pinna function

Answer 24

Collects or amplifies sound

Particularly frequencies associated with human speech

Question 25

2 muscles that stabilize the middle ear

Answer 25

Tensor tympani

Stapedius

Question 26

3 functions of the middle ear

Answer 26

Air-to-liquid sound transduction
Amplification
Filtering sound (low frequencies, loud noises)

Question 27

3 cavities of the cochlea and what fluid they contain

Answer 27

Scala vestibuli and scala tympani contain perilymph

Scala media contains endolymph

Question 28

Tectorial membrane

Answer 28

Cilia of the hair cells project into this membrane

Doesn’t move - the movement of the basilar membrane pushes the hair cells into this membrane

Question 29

Helicotrema

Answer 29

Apex of the cochlea

Question 30

How many rows of auditory hair cells are there in the organ of corti?

Answer 30

4 rows

1 row of inner, 3 rows of outer

Question 31

The basilar membrane at the base of the cochlea is more easily displaced by [low/high] frequency sounds

Answer 31

High

At the apex, low frequencies are more effective