Ear

Question 1

Endolymph and perilymph

Answer 1

Endolymph fills the the membranous labyrinth
and perilymph surrounds it.
• Endolymph is rich in K+
-Perilymph low in K+.

• Potential difference is crucial for hair cell
functioning.
• Volumes of perilymph and endolymph are tightly
controlled.
• Overproduction will lead to both vestibular and
auditory symptoms.

Question 2

The Labyrinthine (Inner Ear) Infarction

Answer 2

• Usually occurs with a thrombotic narrowing of AICA (which gives off the labyrinthine artery which supplies the ear)
or the basilar artery at AICA’s opening.

• Labyrinthine infarction is usually associated with
infarction of the brainstem and cerebellum within
AICA’s territory (pons).

• May present with primary vestibular dysfunction or
primary auditory dysfunction.

Question 3

Benign Paroxysmal Positional Vertigo (BPPV)

Answer 3

Cause: otoconia detaching from the otolithic membrane of
the utricle and getting stuck in a semicircular canal.
Head movements may cause the otoconia to move and stimulate the
cupula of the semicircular canal.

Question 4

What do each of these function as

Lateral vestibular nucleus
Medial and superior vestibular nucleus
Inferior vestibular nucleus

Answer 4

1. Lateral vestibular nucleus - control of posture, vestibulospinal reflexes
2. Medial and superior vestibular nuclei - vestibulo-ocular reflexes, vestibulo cervical reflexes (thalamus)
3. Inferior vestibular nucleus - integration of inputs from vestibular labyrinth and cerebellum

Question 5

Lateral Vestibulospinal Tract

Answer 5

Lateral Vestibulospinal
Tract
– Principal pathway by
which otolithic organs
can regulate bodies and 
extensor organs
– Ipsilateral projections 
– Major source: LVN 
– Minor contribution SupVN

Question 6

Medial vestibulospinal tract

Answer 6

Medial Vestibulospinal
Tract

• mainly cervical
• vestibulo-cervical reflexes
• bilateral : projects through MLF

Question 7

Ménière’s Disease

Answer 7

An overproduction of endolymph increases pressure and damages hair cells.

Severe tinnitus

Question 8

Explain the concept of a rightward nystagmus

Answer 8

If you have a horizontal nystagmus due to left ear damage, eyes will slowly move to the left (because it is perceived that your head is moving to the right) and then eyes will snap back. That snap back will give it the name. So we would call it a rightward nystagmus even though damage is on left side.

Question 9

Elaborate and Rinne and Weber results

tbd..

Answer 9

Weber: midline

-tells you if bone conduction is equal on both sides because you are bypassing air.

Question 10

Waardenberg Syndrome:

Answer 10

Waardenberg Syndrome:
(neural crest migration disorder)
characterized by deafness and pigment cell deficiencies.

Pigment cell loss also leads to the absence of hair cells. There is a lack of intermediate cells in the stria vascularis of the inner ear. These cells are neural crest derived melanocytes that produce endolymph. Without them, the endolymph channel collapses and hair cell degeneration occurs.

Question 11

Inner vs outer hair cells

Answer 11

• Inner Hair Cells: Detection of sound.
-inner hair cells are stimulated by fluid movements.
-mostly ipsilateral innervation; lateral
olivocochlear bundle; axo-axonic contacts with
bipolar cells.

• Outer Hair Cells: Participate in the
amplifying and dampening of the
sound stimulus.
– Outer hair cells contract and elongate in synchrony with sound-evoked receptor potentials—due to the actions of the motor protein prestin.
-so outer hair cells have a MOTOR aspect: they can change the gain by contracting, moving the tectorial membrane to move the inner hair cells
-Stereocilia of outer hair cells are embedded in the tectorial membrane; inner hair cells’cilia are not. • As basilar membrane vibrates, the stereocilia are
bent: outer hair cells by shearing action
-mostly contralateral innervation;
medial olivocochlear bundle; direct synaptic contacts.

Question 12

Describe the basillar membrane

Answer 12

• the base is closest to the oval window
• the base is stiff and for high frequencies
• the apex is floppy for low frequencies,

Question 13

“Too Much Sensitive INfo LArry

Answer 13

Time differences: Since the ears occupy different points in space, sound coming from the right arrives at the right ear before the left ear (Medial
Superior Olivary nucleus). Low
frequency best.

• Intensity differences: The head
acts as a baffle.  Sound coming
from the right is more intense
on the right than on the left
(Lateral Superior Olivary
Nucleus).  High frequency
sound best. (low frequency waves are so large it just wraps around)

Question 14

How are the hemispheres different when it comes to listening?

Answer 14

left and right auditory cortex are different

the LEFT auditory tends to be larger , most right handed individuals, speech is localized on the left cortex.
The left primary auditory cortex is larger because of this.

Recognition of music tends to be on right side, lesions on either can affect music or speech perception

Question 15

What is the efferent innervation of inner and outer hair cells

Answer 15

Origin: Superior Olivary Nucleus

Inner hair cells: efferent come from lateral olivocochlear bundle, ipsilateral, axo-axo connections

outer hair cells: efferents come from the medial olivocochlear bundle, contralateral, direct

Question 16

scarpa’s ganglion

Answer 16

Scarpa’s reports sensory information from the vestibular system (spiral ganglion for the cochlear system).

Afferents from scarpa’s ganglion will synapse on the medial vestibular nucleus (vestibulo-ocular reflexes) which will then go either stimulate or inhibit an abducens nucleus so eye turns in the opposite direction of perceived head turning.