Innervation of Inner Ear

Question 1

Vestibular Nerve

Answer 1

Branch of VIII

vestibular nuclei: point where VIII enters, innervates crista and utricle and saccule
sensory ganglion cells are clustered

Question 2

Cochlear Division

Answer 2

afferent

runs as 1 single body where it enters boundary of cochlear nucleus and splits

Cochlear Nucleus: dorsal, ventral

Somas in Rosenthal’s canal near scala tympani

Question 3

Afferent Cochlear Division

Answer 3

Spiral ganglion

Somas in Rosenthal’s Canal
Type I and Type II

Both cross through habenula perforata
spiral ganglion–>osseous spiral lamina–> habenula perforata–>organ of corti

Question 4

Radial Afferents

Answer 4

Type I cochlear division afferents–IHC
80-95% of all spiral ganglion cells
large, myelinated cell bodies with rounded nucleus

divergent innervation 1 IHC to many type 1 cells (10-30), typically contacts without branching

short unmyelinated segment in organ of corti, action potentials at the synapse

Question 5

Spiral afferents

Answer 5

Type II cells connect to OHC
5-20% of all spiral ganglion cells
unmyelinated cell bodies with irregular shaped nucleus and small

enter habenula–cross floor of organ of corti between pillar cells feet–join one of three outer spiral bundles–spiral (100-600 microns in basal direction)–branch extensive and make multiple contacts with many different OHC

Convergent

Question 6

Efferent Innervation

Answer 6

Olivocochlear Bundle

Medial or Lateral System

Question 7

Lateral System/spiral efferents

Answer 7

Originate near lateral superior olive
target=IHC

intraganlionc spiral bundle spiral in rosenthal’s canal near scal tymanpi, split from intraganglionic spiral bundle enter organ of corti through habenula

Joined by lateral neurons inner spiral bundles (under IHC) form axodendritic synapses with type I radial afferents

Question 8

anastomosis of oort

Answer 8

olivocochlear bundle crosses from vestibular to cochlear division of VIII and leaves brainstem

Question 9

Medial System/radial efferents

Answer 9

cross in middle of tunnel of corti and branch and contact multiple OHC directly

Question 10

Adrenergic Efferent

Answer 10

tip of osseous spiral lamina

blood vessel associated, regulates blood flow
blood vessel independent modulation of afferent activity? Not sure