Vestibular System B&B + Hearing

Question 1

what do the utricle and saccule contain that is vital for their function?

Answer 1

aka otolith organs, contain otoliths: calcium carbonate crystals which sit atop the hair cells and drag the hair cells in response to motion (as they roll)

utricle - horizontal motion
saccule - vertical motion

Question 2

where are the vestibular nuclei located?

Answer 2

beneath the floor of the 4th ventricle in the pons/medulla

receives input from vestibular nerve, many outputs

Question 3

nystagmus

Answer 3

rhythmic oscillations of eye

essentially, R and L CN VIII oppose each other, but when one is lesioned/weak, this can cause sort of wobbling back and forth due to repetitive weakness followed by correction

Question 4

for which direction are jerk nystagmus’ (slow towards, fast away) named?

Answer 4

named for the fast direction

so slow drifting towards L eye with fast correction towards right eye would be called rightward nystagmus

can be left, right, torsional/rotational (CW/CCW), upbeat, downbeat

Question 5

what is the origin of vestibular dysfunction causing left/right or torsional/rotational nystagmus vs upbeat/downbeat?

Answer 5

L/R, torsional/rotational nystagmus is seen with peripheral vestibular dysfunction (inner ear - often benign)

upbeat/downbeat (vertical) nystagmus is seen with central vestibular dysfunction (stroke, tumors - often bad)

Question 6

what type of nystagmus is caused by peripheral vs central vestibular dysfunction?

Answer 6

L/R, torsional/rotational nystagmus is seen with peripheral vestibular dysfunction (inner ear - often benign)

upbeat/downbeat (vertical) nystagmus is seen with central vestibular dysfunction (stroke, tumors - often bad)

Question 7

what are the features of central vertigo (caused by stroke, tumors, etc)? (5)

Answer 7

1. vertical (up/downbeat) nystagmus
2. nystagmus changes direction with gaze (may be down when looking to the left while up when looking to the right)
3. immediate nystagmus with positional testing
4. diplopia + dysmetria (fail finger to nose)
5. other CNS symptoms (this makes sense !)

Question 8

what are the features of peripheral vertigo (caused by problem within inner ear)? (4)

Answer 8

1. mixed horizontal/torsional nystagmus
2. delayed nystagmus with positional testing (maybe 10-15s)
3. nystagmus may fatigue with time (slows down after a few seconds)
4. normal proprioception, stable Romberg

Question 9

how is positional testing in a patient with vertigo performed?

Answer 9

Dix-Hallpike maneuver: reproduces vertigo to cause nystagmus

seated patient turns head to the side and rapidly lays down, letting head hang over end of table - look for nystagmus

Question 10

Dix-Hallpike maneuver

Answer 10

reproduces vertigo to cause nystagmus

seated patient turns head to the side and rapidly lays down, letting head hang over end of table - look for nystagmus

Question 11

A pt presents with visual complaints. You instruct the patient to turn their head to the side and rapidly lay down with their head hanging over the edge. After 10 seconds, you note torsional nystagmus, which improves when the patient sits up. This same maneuver is tried 3 times, each with less of a reaction. How do you interpret these results? What is the MOST LIKELY cause of their symptoms?

Answer 11

Dix-Hallpike Maneuver

results indicate peripheral vertigo - most often due to benign positional vertigo (BPV)

this is as opposed to central vertigo, which usually has more serious cause and presents with immediate up/downbeat (vertical) nystagmus

Question 12

what is the cause of benign positional vertigo (BPV)? how is it diagnosed and treated?

Answer 12

due to calcium debris in semicircular canals (canalithiasis)

diagnose via Dix Hallpike Maneuver (delayed horizontal or rotational nystagmus)

treat with Epley maneuver - done repeatedly by physical therapist, similar to Dix Hallpike, repositions otoconia (ear stones)

Question 13

what is the cause of vestibular neuronitis?

Answer 13

aka labrynthitis - causes peripheral vertigo

neuropathy of vestibular portion of CN VIII following viral/post-inflammatory state

benign, self-limited

Question 14

how does Meniere’s Disease present? (3)

Answer 14

endolymph fluid accumulation (hydrops) causing swelling of labyrinthine system

—> tinnitus, sensorineural hearing loss, peripheral vertigo

tx: avoid high salt foods, vasoconstrictors (caffeine, nicotine), diuretics

Question 15

Angular accelerations are detected by the _____

Linear accelerations are monitored by the _____

Answer 15

Angular accelerations are detected by the semicircular canals.

Linear accelerations are monitored by the otolithic organs (utricle + saccule)

Question 16

thickened epithelium populated by hair cells within the semicircular canals

Answer 16

ampullae (ampullary crest)

Question 17

Bending of the stereocilia towards the kinocilium = _____;

bending away = _____

Answer 17

Bending of the stereocilia towards the kinocilium = depolarization;
bending away = hyperpolarization

similar with hearing: Bending the stereocilia towards the basal body leads to depolarization; bending away leads to hyperpolarization.

Question 18

how are hair cells oriented in the utricle vs the saccule (otolithic organs)?

Answer 18

utricle: macula contains hair cells in horizontal plane - responds to tilting of the head (causes bending of stereocilia)

saccule: macula contains hair cells in vertical plane - responds to linear acceleration in sagittal or vertical plane

Question 19

Upward deflection of the basilar membrane (of inner ear)
results in ______

Downward deflection of the basilar membrane results in ______

Answer 19

Upward deflection of the basilar membrane
results in depolarization

Downward deflection of the basilar membrane results in
hyperpolarization

Different regions of the basilar membrane are selectively responsive to different frequencies of sound. The basilar membrane is stiff near the oval window (high frequency) and flexible near the apex (low frequency)

Question 20

the auditory cortex is located on the ______ gyrus

Answer 20

superior temporal gyrus (transvers gyrus of Heschel)