CN VIII: Vestibulocochlear Flashcards
(30 cards)
Inner ear embedded in which cranial bone?
temporal
Two portions of inner ear and associated fluids
membranous inside bony labyrinth (for vestibular) or cochlea (for auditory) Membranous: -endolymph: low Na, high K -hair cells Bony: -perilymph: high Na, Low K
endolymph path
- produced in membranous labrinth
- leaves via endolymphatic duct
- to endolymphatic sac in dura
- reabsorbed into venous system
vestibule
central enlarged region of bony labrynth
ampullae
dilation at one end of each semicircular canal closest to utricle
pairs of semicircular canals
L and R horiz
L post and R ant
L ant and R post
-Because they’re in the same plane
Utricle/Saccule
Utricle is horizontal
Saccule is vertical
- detect linear acceleration in their plane and info on static head position
- in bony vestibule
Kinocilium
- next to tallest hair cell
- only important for development
- oriented towards utricle in horizontal canals (opposite in ant/post canals)
Vestibular hair cells (semicircular canals)
structure/location
- apical stereocilia into endolymph
- release glutamate to CN VIII basally
- in cristae in ampullae
Vestibular hair cells
on/off
- bending towards kinocilium ON, away is OFF
- on via mechanically gates K channels-> K into cell-> VG Ca channels open -> glutamate released
- Note: always baseline NT release
Cristae
- in ampullae of semicircular canals
- hair cells embedded in cupula
- cupula extends width of ampulla
—>endolyph will move in OPPOSITE direction of rotation
Vestibulo-ocular reflex
pathways
- allow fixation on object when head is moving
- in from sensory afferents in ear
- out bilaterally to abducens, throchlear, occularmotor nuclei for eye movement via MEDIAL LONGITUDINAL FASCICULUS
Maculae
- location of hair cells in utricle/saccule (1 in each)
- hair cells embedded in otolithic membrane containing otoconia/otoliths (carbonate crystals)
Striola
- line in macula which hair cells are aligned along
- arranged such that any movement causes excitation of some hair cells and inhibition of others.
- bean shaped
Vestibulo thalamo-cortical pathway
lateral and superior vestibular nuclei project to VPL of thalamus -> parietal cortex -> near the face representation of post central gyrus
Vestibulo-ocular reflex
left rotation, response
- L rotation of head
- Excitation of L horizontal semicircular canal
- Increase contraction of L medial rectus and R lateral rectus
- Decrease contraction of L lateral rectus and R medial rectus
Auricle
AKA pinna
outer ear
muscles of middle ear
function, attachement, CN
- to dampen vibrations
- tensor tympani
- attached to malleus (CN-V)
- stapedius
- attached to stapes (CN-VII)
What kind of joints connect the ossicles?
synovial
Cochlear duct
AKA membranous cochlea
Helicotrema
turn or ‘end’ of cochlea where perilymph reverses direction down the other side of the cochlear duct
vestibular membrane
top membrane of cochlear duct (closest to oval window)
basilar membrane
location/function
- bottom membrane of cochlear duct (closest to round window)
- location of organ of corti
- stiff at cochlear base (by oval and round windows)
- flexible at cochlear apex
Scala vestibuli vs media vs tympani
- scala vestibuli: space above cochlear duct
- scala media: space inside cochlear duct (triangular)
- scala tympani: space below cochlear duct
