Vestibular and Auditory Systems Flashcards
Perilymph
Outside the labyrinth and in 2 canals of the cochlea
Fills the space between bony and membranous labyrinths
Composition similar to extracellular fluid and CSF (low K, high Na)
Ultrafiltrate of CSF or blood
Drains via venules and middle ear mucosa
Endolymph
In the lumen of the semicircular canals, utricles, and saccules
Unique fluid similar to intracellular fluid (high K and low Na)
Produced by the dark cells of the sensory epithelium
Absorbed by the endolymphatic sac
Vestibular system function
Detects body position relative to gravity and the motion of body in space
Equilibirum (balance and postural stability)
Motor output (reflex and controlled)
Vision (control of head and eye motion and stabilizing visual gaze)
Semicircular canals detect…
Angular acceleration (= head rotations)
Each of the 3 canals is sensitive to head rotations in the plane of that canal
Together they can specify the direction and amplitude of any head rotation
Otolithic organs (utricle and saccule) function
Sense body orientation and linear motion
Utricle: horizontal
Saccular: vertical
Ductus reuniens
Connects the utricle and saccule to the cochlea
Hair cells
Excitatory neurons that release glutamate
In the cochlea, utricle, saccule and semicircular canals
Each cell has several cilia projecting from its apical pole
Base of cell is surrounded by receptive terminals of CN 8
Orientation of stereocilia on hair cells
Oriented in rows of ascending height
Tallest is nect to the single kinocilium
Cilia are linked together by filaments
What happens to the hair cell when the stereocilia are bent
- Towards to kinocilium
- Away from the kinocilium
- Depolarized
2. Hyperpolarized
Parts of the semicircular canals
Ampulla (swellings at the ends)
Cristae (hair cell sensory epithelium in the ampulla)
Cupula (acellular, gelatinous mass
What structures control the position of the eyes during the vestibulo-ocular reflex?
Semicircular canals
Parts of the utricle and saccule
Contain a macula (= to crista of canals, so contain hair cells)
Hair cells project into the otolith membrane
Membrane contains the otoconia (rocks)
Respond to gravity and linear acceleration
Main role of utricle and saccule
Cause reflex adjustments (head position via neck and trunk muscles, body position via limb muscles)
4 vestibular nuclei (where from, what to)
Superior (from canals to MLF for eye movement coordination)
Medial (from utricle and saccule to neck and trunk)
Lateral (from U and S to limbs)
Inferior (receives input from all components and projects to cerebellum which coordinates all motor activities and modulates VOR)
Benign Paroxysmal Positional Vertigo
Displaced otoconia lodged in the semicircular canals
Meniere’s Disease (endolymphatic hydrops)
Increased endolymph in inner ear
Vestibular neuritis
Viral infection of the vestibulo-cochlear nerve
Perilymph fistula
Breach in the oval and/or round window
Ototoxicity
Toxicity induced death of hair cells
Mal de Debarquement
Failure of CNS plasticity to respond to prolonged movement
Like not being able to adjust after having sea legs
How does aging impact the vestibular system?
Gradual loss of hair cells
Normally compensated by vision, but can be a problem in the dark or with eyes closed
Is bilateral or unilateral vestibular dysfunction more severe?
Unilateral
What does
1. Frequency
2. Amplitude
translate to?
- Pitch
2. Loudness
Auricle/Pinna function
Collects or amplifies sound
Particularly frequencies associated with human speech
2 muscles that stabilize the middle ear
Tensor tympani
Stapedius
3 functions of the middle ear
Air-to-liquid sound transduction
Amplification
Filtering sound (low frequencies, loud noises)
3 cavities of the cochlea and what fluid they contain
Scala vestibuli and scala tympani contain perilymph
Scala media contains endolymph
Tectorial membrane
Cilia of the hair cells project into this membrane
Doesn’t move - the movement of the basilar membrane pushes the hair cells into this membrane
Helicotrema
Apex of the cochlea
How many rows of auditory hair cells are there in the organ of corti?
4 rows
1 row of inner, 3 rows of outer
The basilar membrane at the base of the cochlea is more easily displaced by [low/high] frequency sounds
High
At the apex, low frequencies are more effective
