Hearing and Balance

Question 1

Hearing and balance are both innervated by which cranial nerve ?

Answer 1

Both housed in the ear, innervated by CN CIII:

Chchlea branch convey sound

Vestiular branch conveys head position/motion

Question 2

In the temporal bone : ___ (outside) and ___ (inside)

Answer 2

In the temporal bone : bony labyrinth (outside) and membranous labyrinth (inside)

Question 3

_________ ; semicircular duct inside canal

Answer 3

Cochlear duct; semicircular duct inside canal

Question 4

Cochlear duct attaches to the ____, semicircular ducts attach to the ___, ___ connected to utricle

Answer 4

Cochlear duct attaches to the saccule, semicircular ducts attach to the utricle, saccule connected to utricle

Question 5

____ in bony labyrinth - like csf and continuous with subarachnoid

Answer 5

Perilymph in bony labyrinth - like csf and continuous with subarachnoid

Question 6

Blockage of fluid causes ?

Answer 6

Blockage of fluid (like hydrocephalus) causes Meniere’s disease , vertigo , nausice, hearing loss

Question 7

Describe receptrors (Hair cells), and cranial nerve attached, their location

Answer 7

hair cells (purple) with microvilli extending from top:

Tallest is kinocilium (f?) others are stopped in height - stereocilia

Two tallest microvilli enter gelatinous mass

Each microvilli attached to the next tallest by tip links. : each tip link has ion channel

Microvilli are in endolymph but base of hair cells is in perilymph where synapses to CN VIII

Endolymph and perilymph separated by barrier of tight junctions of cells.

location

6 discrete locations (1 on each base of semicircular disc , 1 on utricle , 1 in saccule 1 stripe that winds cochlear duct.)

Question 8

What are the components of ear, location ? what are they filled with ?

Answer 8

Outer ear (up to eardrum)

Middle ear (inner eardrum and ossicles)

inner ear (cochlea)

outer eat and middle ear are filled with air

inner ear filled with fluid

air (sounds) have to pass through both to detected.

Question 9

Describe flow of sound from ear canal to organ of Corti

Answer 9

Sound enter ear canal, vibrates tympanic membrane (eardrum) , vibrates ossicles (alleus -> incus -> stapes) goes through oval window to vestibular to cochlea to organ of Corti

Question 10

what muscles attached to ossicles ?

Answer 10

Sound transformed though ossicles

2 muscles attache to ossicles:

tensor tympani - innervated by trigeminal

stapedius - innervated by facial

Question 11

Describe organ of Corti.

Answer 11

Once inside the cochlea the sound waves travel to the organ of Corti (the auditory receptor organ)

Which sits on the basilar membrane

Organ of Corti is a strip of hair cells and support ells . Hair cells are arranged in 2 groups:

3500 inner hair cells : single file

15000 outer hair cells 2-5 wide

Question 12

what properties of sound must be encoded ?

Answer 12

3 properties of sound must be encoded

intensity - coded by rate of AP firing

location - requires comparison of both ears so happens in CNS

frequency - determined by which part of organ of Corti is most active:

progressively higher frequencies as move from apex to base of cochlea

provide mechanical tuning system that end up .. etc

Question 13

Hair cells

Inner hair cells are the ____ cells

Outer hair cells are ____ (of basilar membrane travelling waves)

Answer 13

Hair cells

Inner hair cells are the sensory cells

Outer hair cells are amplifiers (of basilar membrane travelling waves)

Question 14

describe pathway from brainstem to cortex.

Answer 14

CN VIII enters at pontomedullary junction, branches to dorsal cochlear nucleus and central cochlear nucleus

Ascend the lateral lemniscus , the major auditory pathway of brainstem (some cross midline some don’t so get intro from both ways) to the inferior colliculi

From inferior colliculi to the medial geniculate nucleus of the thalamus

From thalamus to primary auditory cortex in a tonotopical fashion

primary auditory cortex is transitive temporal gyrus (Heschel’s gyrus) in the lateral fissure.

Other fibers leave the cochlear nucleus and end in superior olivary nucleus crossing at trapezoid body

use info from both ears to localise sound by measuring tie of arrival of sound.

Question 15

Tonotopic mapping of pitch in primary auditory cortex (Heschel’s) : Low freq tones are __ and move __ for the high fern tones.

Answer 15

Tonotopic mapping of pitch in primary auditory cortex (Heschel’s)

Low freq tones are lateral and move medially for the high fern tones.

Question 16

what kinds of hearing damage

Answer 16

Hearing Damage

Conduction - sound doesn’t reach the labyrinth

Sensorineural - damage to hair cells or cochlear nerve fibers of the cochlear nuclei

Audiograms from tests of air conduction and bone conduction of sound can be used to dx which type of loss

bone conduction problem would indicate sensorineural loss

impaired air but preserved bone conduction would indicate conduction loss

Question 17

Each semicircular canal ends with a bulge - ______

Answer 17

Each semicircular canal ends with a bulge - ampulla

Question 18

describe how vestibular function work

Answer 18

1 semicircular duct receptors detect angular acceleration of the head

one end semicircular duct has an ampulla

Inside ampulla is a ridge if tissue covers hair cells receptors allied crista

Attached to crista is CN VIII

Gelantinous mass above crista in which stereo cilia project - c u p u l a and extends to the top of the amuplla (spilling in half )

Question 19

no crista in utricle and saccule , instead have _____

Also embedded in gelantinous mass but this one has crystals in it (______)

Answer 19

no crista in utricle and saccule , instead have macula

Also embedded in gelantinous mass but this one has crystals in it (otoliths)

Question 20

how Utricle and saccule detect linear acceleration and head position ?

Answer 20

Makes the membrane denser than fluid to when head moves membrane globs to one side and stays there and hair cells are moved and send signal to CN VIII fivers to report new head position

Question 21

utricle detects acceleration in ____

saccule detects acceleration in ______

Answer 21

Detect linear acceleration

utricle (acceleration in horizontal plane: car ride)

saccule - (acceleration in vertical plane: elevator)

Question 22

describe the path from ear to cortex

Answer 22

auditory canals to vestibular nuclei on brainstem and to the Cb

Vestibular nuclei to lots of places

Vestibular sense enables us to regulate our posture and coordinate eye and head movement:

so sends projections to spinal cord , Cb

brainstem nuclei of CN III IV VI (eye movement)

visceral autonomic response (sick from roller coaster)

thalamus (VPL) to cortex for propioceptive movement through space

mostly parietal (btw intraparietal and postcentral gyri) which is near body position potion of sensory strip

posterior insula( near auditoy cortex)

Question 23

Eye movement compensate for changes in head movements.

__________ comes from CN ______ nuclei (eye movement)

Answer 23

Eye movement compensate for changes in head movements.

Vestiblulo-occular reflex (VOR) comes from CN III IV VI nuclei (eye movement)

Question 24

________ illusions of movement in response to certain orientations of the head.

Answer 24

Vertigo illusions

illusions of movement in response to certain orientations of the head (vertigo)

Question 25

combined at level of ____ where ___ , ___, and ___ input coverage

if 1 of the 3 sense is impaired , the other two can compensate.

Answer 25

combined at level of vestibular nuclei where visual , somatosensory, and vestibular input coverage

if 1 of the 3 sense is impaired , the other two can compensate.

Question 26

________ - can balance fine with eye open but when close eyes there is swaying and loss of balance.

Answer 26

Rombeg’s sign- can balance fine with eye open but when close eyes there is swaying and loss of balance.