Vestibular System

What does the cochlea do?

Converts air vibrations to neural signals that encode frequency, intensity, location of sound

What are three compartments of the organ of corti (cochlea)?

Scala Vestibuli- sound input

Scala Media- sound detection, contains hair cells

Scala Tympani- sound output

How does activation occur in scala media?

Basilar membrane vibrates, causes stereocilia to push against tectorial membrane

Basilar membrane frequency range and where?

Base is high pitch, Apex is high pitch

Tectorial membrane helps send AP to - nerve, through hair cell - (opens - channels and release -)

Auditory, bending (ion, Glutamate)

What does the vestibular apparatus consist of?

3 semicircular canals (anterior, posterior, horizontal)

2 otolith organs (utricle, saccule)

What do utricle and saccule detect?

Utricle: detects linear acceleration in horizontal plane

Saccule: detects linear acceleration in vertical plane

Semicircular canals detect - -

Angular acceleration

What gelatinous structure is for SC vs OO?

SC: cupula

OO: macula

Ends of each canal has an -, which houses the -. Inside of this structure, there is - that can displaces the - - in it to create a neural signal

Ampulla, cupula. Endolymph, hair cells

Explain hair cell depolarization!

Movement of hair cells toward kinocilium excited CN VIII, movement away inhibits

Head right= endolymph _ and R kino _ and L kino _

L, +, -

Otoconia are where and what do they respond to?

Sit on top of otolith organs, respond to head tilt

What are the four major vestibular nuclei?

1. Superior nucleus- contributes to VOR

2. Medial nucleus- controls head and neck movements

3. Lateral nucleus- controls posture and balance

4. Inferior nucleus- integrates signals from the cerebellum and spinal cord

What is VSR and what is the difference between lateral and medial tracts?

Coordinates head/neck movement with rest of body

• Medial: orients/stabilizes head

• Lateral: postural changes (extensors) to compensate for tilt

For VOR, eyes move - and - to head

Equal and opposite

Nystagmus explanation (R vestibular damage)

R damage → Increased L firing → Brain thinks head is moving L → Eyes drift R → L corrective saccade

Eye drift in - direction as damage, Saccade in -

Same, opposite

What is BPPV?

Vertigo caused by sloughing off of otoconia from utricle and moved to semicircular canals, endolymph continues to move after head stops and canal becomes gravity-sensitive

What tells a clinician where the otoconia are loose?

Direction and length of eye movement

Inferior vestibular nerve innervates what two structures? All else are innervated by what?

IVN: saccule, posterior canal

Superior vestibular nerve: saccule + all else