CN VIII: Vestibulocochlear

Question 1

Inner ear embedded in which cranial bone?

Answer 1

temporal

Question 2

Two portions of inner ear and associated fluids

Answer 2

membranous inside bony labyrinth (for vestibular) or cochlea (for auditory)
Membranous: 
   -endolymph: low Na, high K
   -hair cells
Bony:
   -perilymph: high Na, Low K

Question 3

endolymph path

Answer 3

• produced in membranous labrinth
• leaves via endolymphatic duct
• to endolymphatic sac in dura
• reabsorbed into venous system

Question 4

vestibule

Answer 4

central enlarged region of bony labrynth

Question 5

ampullae

Answer 5

dilation at one end of each semicircular canal closest to utricle

Question 6

pairs of semicircular canals

Answer 6

L and R horiz
L post and R ant
L ant and R post

-Because they’re in the same plane

Question 7

Utricle/Saccule

Answer 7

Utricle is horizontal
Saccule is vertical

• detect linear acceleration in their plane and info on static head position
• in bony vestibule

Question 8

Kinocilium

Answer 8

• next to tallest hair cell
• only important for development
• oriented towards utricle in horizontal canals (opposite in ant/post canals)

Question 9

Vestibular hair cells (semicircular canals)

structure/location

Answer 9

• apical stereocilia into endolymph
• release glutamate to CN VIII basally
• in cristae in ampullae

Question 10

Vestibular hair cells

on/off

Answer 10

• 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

Question 11

Cristae

Answer 11

• in ampullae of semicircular canals
• hair cells embedded in cupula
• cupula extends width of ampulla

—>endolyph will move in OPPOSITE direction of rotation

Question 12

Vestibulo-ocular reflex

pathways

Answer 12

• 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

Question 13

Maculae

Answer 13

• location of hair cells in utricle/saccule (1 in each)

- hair cells embedded in otolithic membrane containing otoconia/otoliths (carbonate crystals)

Question 14

Striola

Answer 14

• 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

Question 15

Vestibulo thalamo-cortical pathway

Answer 15

lateral and superior vestibular nuclei project to VPL of thalamus -> parietal cortex -> near the face representation of post central gyrus

Question 16

Vestibulo-ocular reflex

left rotation, response

Answer 16

• 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

Question 17

Auricle

Answer 17

AKA pinna

outer ear

Question 18

muscles of middle ear

function, attachement, CN

Answer 18

• to dampen vibrations
• tensor tympani
  
  • attached to malleus (CN-V)
• stapedius
  
  • attached to stapes (CN-VII)

Question 19

What kind of joints connect the ossicles?

Answer 19

synovial

Question 20

Cochlear duct

Answer 20

AKA membranous cochlea

Question 21

Helicotrema

Answer 21

turn or ‘end’ of cochlea where perilymph reverses direction down the other side of the cochlear duct

Question 22

vestibular membrane

Answer 22

top membrane of cochlear duct (closest to oval window)

Question 23

basilar membrane

location/function

Answer 23

• 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

Question 24

Scala vestibuli vs media vs tympani

Answer 24

• scala vestibuli: space above cochlear duct
• scala media: space inside cochlear duct (triangular)
• scala tympani: space below cochlear duct

Question 25

osseous spiral lamina

Answer 25

bony projection into the cochlea

Question 26

Auditory hair cells

structure/location

Answer 26

• apical stereocilia project into endolymph in cochlear duct
• stereocilia tips embedded in tectoral membrane (outer hair cells)
• basal NT release to CN VIII

Question 27

How does cochlea distinguish high vs low notes?

Answer 27

differences in basillar membrane stiffness
stiff at base for high notes
flexible at apex for low notes

TONOTOPICALLY ORGANIZED

Question 28

Auditory pathway

Answer 28

Cochlea -> spiral/cochlear ganglion -> cochlear nucleus/pontomedullary jxn -> BILATERAL to superior olive (majority decussate via trapazoid body) -> Inferior colliculus via lateral lemniscus -> medial geniculate nucleus in thalmus -> auditory cortex (A1;41/42)

Note: some neurons bypass the superior olive and go straight from cochlear nucleus to inferior colliculus

Question 29

How does brain distinguish location of sound?

Answer 29

Brain compares differences in synaptic timing between fibers travelling from cochlear nucleus to superior olive directly and those decussating along trapazoid body (and compares for input from both ears)

Question 30

Where do auditory fibers cross contralaterally? (3)

Answer 30

• trapezoid body
• inferior colliculus
• medial geniculate nucleus