Auditory System

Question 1

Three compartments of the ear

Answer 1

Outer: external auditory meatus which magnifies sound by passive resistance. Pinna which is for localizing sound in vertical plane.

Middle: Malleus Incus Stapes, tensor typani (which improves high frequency hearing), stapedius (which pulls stapes off oval window

Inner: Cochlea, semicircular canals, otolith organs

Question 2

Structure of cochlea

Answer 2

Bony cochlea: filled with perilymph (high Na, low K)

Membranous cochlea: filled with endolymph, more aqueous (high K, low Na)

Question 3

Input/output of waves at cochlea

Answer 3

Input at scala vestibuli, output at scala tympani. Scala media in middle filled with endolymph

Question 4

Organ of corti

Answer 4

One row of inner hair cells at basal membrane (95% of auditory nerve), three rows of outer hair cells.

Question 5

Inner vs outer hair cells

Answer 5

Inner, actual hearing. Outer hair cells receive input from the superior olive via olivocochlear bundle, sharpen the sound frequency resolution by modulating the position of the tectorial membrane.

Question 6

Outer hair cells receive input from?

Answer 6

Superior olive

Question 7

Hair bundle displacement towards kinocilium? Away?

Answer 7

Towards = depolarization. Away = hyperpolarization

Question 8

Structure of the basilar membrane

Answer 8

Wider and thinner as it winds in cochlea. Lower frequencies at end (helicotrema).

Question 9

Where do aminoglycosides act?

Answer 9

Poison outer hair cells

Question 10

Otoacoustic emissions

Answer 10

Vibration of outer hair cells

Question 11

Cell bodies for auditory nerve located where?

Answer 11

In the modialus in spiral ganglia.

Question 12

Do hair cells make synaptic contact with auditory nerve?

Answer 12

Yes

Question 13

Auditory pathway

Answer 13

Cochlea inputs to cochlear nucleus, which projects bilaterally to two superior olives. Which project up to inferior colliculus via the lateral lemniscus, which project to MGN, which project to A1 in the temporal lobe (Heschel’s Gyri).

Question 14

Is hearing binaural?

Answer 14

Yes of course, once you get past the cochlear nucleus. This serves to ensure that sound can be localized temporally and by intensity

Question 15

Two ways to localize sound in superior olive

Answer 15

By intensity (high freq) and by timing (low freq).

Question 16

Olivocochlear bundle

Answer 16

Projections from superior olive to outer hair cells to control auditory attention and noise masking

Question 17

Lateral lemniscus

Answer 17

Projections from superior olive to inferior colliculus

Question 18

heschel’s gyri

Answer 18

Receive input from MGN, projections duck under internal capsule. Also tonotopically encoded.

Question 19

Semicircular canals sense…?

Answer 19

Where am I going?

Question 20

Otolith organs sense…?

Answer 20

Which way is up?

Question 21

Vestibulothalamocortical projections

Answer 21

Conscious perception of equilibrium

Question 22

Vestibuloocular reflex

Answer 22

Maintains stable gaze

Question 23

Vestibulospinal projections

Answer 23

Maintains postural equilibrium, head stability during body movements. Includes vestibulocolic.

Question 24

Vestibuloautonomic reflex

Answer 24

Compensatory changes in BP, respiration, and digestion with changes.

Question 25

Peripheral sensory apparatus

Answer 25

Semicircular canals and otolith organs, project to four vestibular nuclei

Question 26

Three semicircular canals

Two otolith organs

Answer 26

Anterior, posterior, lateral. Utricle, saccule

Question 27

Structure of semicircular canals

Answer 27

Bony structures that are filled with perilymph. Contain membranous sacs that are filled with endolymph.

Question 28

Crista ampullaris

Answer 28

Sensory sheet within the ampulla that contains hair cells and supporting cells. These hair cells are lodged in a gelatinous cupula.

Question 29

Bilateral coupling of semicircular canals

Answer 29

LARP
RALP
Horizontals together

Question 30

Saccule detection

Answer 30

Vertical plane (which way is up?)

Question 31

Utricle detection

Answer 31

Translation

Question 32

Maculae

Answer 32

Sensory sheets of otolith organs that are covered in otoconia, which make the membrane heavier.

Question 33

Scarpa’s Ganglion

Answer 33

Where the cell bodies of the vestibular nerve are located.

Question 34

The names of the four vestibular nuclei?

Answer 34

Superior
Inferior
Medial
Lateral

Question 35

Vestibulothalamocortical projections

Answer 35

Vestibular nerve projects to superior and lateral vestibular nuclei. This projects to VP of thalamus, which projects to the vestibular cortex located in the posterior parietal lobe.

Question 36

Vestibuloocular Reflex

Answer 36

More to come on this!

Question 37

Vestibulospinal tract

Answer 37

Vestibular nerve projects to lateral vestibular nucleus, which projects to all levels of the ipsilateral spinal cord via lateral vestibulospinal tract.

Question 38

What uses medial vestibulospinal tract?

Answer 38

Vestibulocolic pathway, which maintains head stability during body movement. Medial vestibular nuclei project BILATERALLY to the cervical spinal cord (via MLF)

Question 39

Vestibular system connections with the cerebellum

Answer 39

Very important.

Question 40

Weber and Rinne

Answer 40

W: tuning fork on top of head. Lateralizes towards a conductive hearing loss, away from a sensorineural hearing loss.

R: Tuning fork behind the ear, AC>BC, normal or sensorineural. BC>AC, conductive hearing loss.

Question 41

Noise induced hearing loss

Answer 41

audiogram shows sharp decline at 4K HZ

Question 42

Meniere’s Syndrome

Answer 42

Episodic vertigo, lasts hours at a time. Created by too much fluid in semicircular canals, also causes hearing loss

Question 43

Benign Paroxysmal Positional Vertigo

Answer 43

otoconia dislodge and drift into posterior semicircular canal. Diagnose with Dix Hallpike maneuver, correct with epley.