Organ of corti (cochlear hair cells)

(bipolar nerves) spiral (or cochlear) ganglion

cochlear nerve

synapse -> Neurons in these nuclei send both crossed and uncrossed axons -> trapezoid body and some of them synapse in the superior olivary nuclei (distance) -> The ascending fibers course in the lateral

lemnisci ->

medial geniculate body

primary auditory cortex

* inferior colliculi and medial geniculate bodies each receive

impulses derived from both ears Reflex connections pass to eye muscle nuclei and other

motor nuclei of the cranial and spinal nerves via the tectobulbar

and tectospinal tracts. These connections are activated by

strong, sudden sounds; the result is reflex turning of the eyes

and head toward the site of the sound. In the lower pons, the superior olivary nuclei receive input from both ascending

pathways. Efferent fibers from these nuclei course along the

cochlear nerve back to the organ of Corti. The function of this

olivocochlear bundle is to modulate the sensitivity of the

cochlear organ.Cochlear nerve damage: hearing loss on ipsilateral earHearing cortex damage on right: bilateral hearing loss but on contralateral site its more

Equilibrium and muscle tonus

Semicircular ducts -> rotational movements of head

Utricle -> vertical and lateral acceleration

Sacule -> linear acceleration

Ampulla in semicircular canals: crista hair cells embedded in cupula

Utricle + sacule: macula hair cells embedded in otholiths

Ampulla of anterior and lateral semicircular canals + macula of utricle -> superior vestibular ganglia

Ampulla of posterior semicircular canal + macula of sacule -> inferior vestibular ganglia

These ganglia are found in fundus deep part of internal acustic meatus.

Fundus 4 parts: 1) posteriosuperior - > superior vest. ganglion 2) posterioinferior -> inferior vest. ganglion

*fibers coming from 2 different canals: posterior

semicircular duct fibers through singular canal and sacule

fibers through saccular vestibular area. The central branches run within the vestibular

component of cranial nerve VIII to enter the brain stem

and end in the vestibular nuclei

sup + lat vest nuclei -> cerebellum where they end in

the cerebellar cortex within the flocculonodular component

lateral vestibular nuclei -> lateral vestibulospinal tracts to spinal cord postural adjustments superior and medial vestibular nuclei -> 1)MLF -> nuclei of the eye muscles

2)medial vesitbulospinal tract - > cervical spinal cord for head movements3)Some vestibular nuclei send fibers to the reticular formation. Some ascending fibers from the vestibular nuclei travel by way of the thalamus VPL to the parietal cortex (area 40). to be conscious about balance.Lateral lemnisci

Inferior colluculi

Brachium