brief anatomy of the vestibular system this slideshow is only a summary, the full intricate microanatomy is out of scope of the presentation

1. S Pandey

2. VESTIBULAR SYSTEM
 provides orientation in
3D space
 Modification of muscle
tone & Balance
 Essential for coordinates
of motor response, eye
movement & posture
 Sense of Balance poorly
represented in centres of
consciousness

3. EMBRYOLOGY

4. Vestibular system
 Peripheral part located in
labyrinth, inner ear
 Vestibule & semicircular
canals dilations & carvings
within petrous temporal
(perilymph)
 Memb labyrinth similar in
shape but smaller
(endolymph)
 Stria vascularis in cochlear
duct & secretory cells in
transitional epithelium
produce endolymph
 Membranous labyrinth
related to vestibular fxn
consist of 3 semicircular
ducts, Utricle and Saccule
 Within these structures
there are neuroepithelial
cells = peripheral receptors
of vestibular system

5. The Semicircular Canals

6. UTRICLE & SACCULE

7. Macula
 Each macula is a small area of sensory epithelium. The ciliary
bundles of the sensory cells project into the overlying statoconial
membrane. The statoconial membrane is comprised of 3 layers,
as follows:
 The otoconial first layer
 The second layer is a gelatinous area of mucopolysaccharide gel.
 The third layer consists of subcopula meshwork.
 The otoconia appear to be produced by the supporting cells of
the sensory epithelium and to be resorbed by the dark cell
region.
 On a morphologic basis, each macula can be divided into 2 areas
by a narrow curved zone that extends through its middle. This
zone has been termed the striola.

8. Crista ampullaris
 Consists of a crest of
sensory epithelium
supported on a mound
of connective tissue
 Bulbous wedge shaped,
gelatinous mass called
cupula surmounts the
crista
 Cilia of sensory cells
project into cupula

9. Vestibular hair cells
 Type 1 & 2
 Sensory cells
 Stereocilia
 Kinocilium
 Supporting cells

10. BLOOD SUPPLY

11. INNERVATION
 Efferent innervation from the e group nucleus of the
brainstem. (200 cell bodies located lateral to abducens
nucleus)
 Fibers project ipsilaterally, contralaterally & bilaterally
 Travel in ventral part of vestibular nerve
 Parasympathetic innervation from intermediate nerve
fibers that become part of vestibular nerve near the
vestibular ganglion after passing through geniculate
ganglion of CNVII
 Post Ganglionic fibers from superior cervical ganglion
 Non vascular sympathetic fibers travel along myelinated
afferent fibers. But do not innervate sensory epithelium of
vestibular organs

12. Vestibular nerve
 Branches into superior
division that innervates
the ant & horizontal
cristae ampullares and
utricular macula
 Inferior division that
innervates post crista
ampullaris & saccular
macula

13. OORT’s ANASTOMOSIS
 The vestibulocochlear anastomosis was first described
in 1918 by von Oort. It is situated deeply at the bottom
of the internal acoustic meatus, and spreads from the
saccular nerve before its terminal ramifications, to the
cochlear nerve before its penetration into the cochlea.
Nerve fibers of the cochlear efferent system are
thought to pass through it.
 VOIT’s nerve (branch of superior vestibular nerve
running to the saccular macula. Also known as
superiour saccular nerve

14. VESTIBULAR NUCLEAR COMPLEX
 4 Nuclei lie on lateral recess of rhomboid fossa
 Lateral nucleus contains largest cells, inferior nucleus
contains smallest cells.
 Form two distinct cell columns
 Medial vestibular nucleus is largest forms medial cell
column
 Superior, lateral & inferior vestibular nuclei form
lateral cell column
 Most of nublei and interconnected through
commisural system

15. Vestibular nuclei complex contd
 Electrical stim of utricular macula evokes excitation in
ipsilateral secondary vestibular neurons & inhibition
in >50% of contralateral secondary vestibular neurons
 Nucleus prepositus hypoglossi
 Parasolitary nucleus
 Nucleus X
 Nucleus Z

16. VESTIBULAR GANGLIA
 2 Ganglia, one on each side
 Cell bodies of afferents innervating peripheral
vestibular apparatus
 Each ganglion contains abt 20000 cells
 Divided into superior & inferior part united by
isthmus
 Peripheral processes from sup ganglion innervate
ampullary crests of sup & lateral semicircular ducts &
macula of utricle
 Inf ganglion innervate macula of saccule

17. Vestibular ganglia contd
•Central processes from
vestibular ganglion form the
vestibular nerve
•Together with cochlear nerve,
vestibular nerve courses in the
internal auditory meatus as
vestibulocochlear nerve
•Passes through
cerebellopontine angle and
enter the pons to terminate in
vestibular nuclear complex
•Few fibers pass directly to
flocculo nodular lobe of
cerebellum
•(primary vestibular fibers)

18. Secondary vestibular fibers
 From medial and inferior vestibular nuclei destined for
flucculo nodular nobe and uvula
 Form all vestibular nuclei travelling within medial
longitudinal fasciculus to reach cranial nerve motor
nerve nuclei (innervating extraocular muscles & axial
musculature of the neck)
 Form the lateral vestibular nucleus to all spinal levels
(forms lateral vestibulospinal tract)

19. Vestibulo- autonomic control
 Radtke et al (2003), subjected patients to abrupt
head acceleration
 Concluded that a delayed increase of HR in
response to postural challenge occurred in patients
with vestibular loss

20. VESTIBULAR PROJECTIONS TO THALAMUS
 Originate from rostral part of vestibular nuclear
complex
 Destined to VPL,VPM,VPI (ventrobasal thalamus)
 Neurons respond to stimulation of deep
proprioceptors and joint receptors as well as vestibular
inputs

21. Vestibular-Hippocampal interactions
 Hippocampus thought to be nb for spatial
representation processes that depend on integration
of both self movement & allocentric cues
 Vestibular system is Nb source of self movement info
 Various parts of thalamus likely to transmit vestibular
information to hippocampus ?via parietal cortex
 More direct pathways possible.
 Studies demonstrate the nb of vestibular hippocampal
interaction for hippocampal fxn, but also suggest
hippocampus nb site for compensation of v. fxn
following lesions (peripheral or central)

22. ?VESTIBULAR CORTEX?
 Does it exist?
 Different areas of primate cortex have been named
“vestibular”
 Guldin & Gurusser defined in 3 diff primate series
 Similar pattern exist in human
 Area 2v at tip of intraparietal sulcus, area 3v in central
sulcus, parietoinsular vestibular cortex next to post
insula and area 7 in inferior parietal lobule involved in
vestibular information processing

23. VESTIBULAR SYSTEM & AGING
 Falling & loss of balance among geriatric population
frequent & serious problem
 Attributed to the progressive deterioration of anatomical
components of vestibular system
 Study investigating quantitive diff in num, density or type
of hair cells or length of crista ampullaris in young & aged
gerbils no diff found. Cause of vestibular dysfxn during
aging should be looked for elsewhere.
 Study regardign age related change in num of neurons in
human vestibular ganglion proved that decline in prim
neurons exist (anatomical basis of increased incidence of
balance seen in age

24. Origins of the Cranial Nerves
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25. Origins of the Cranial Nerves
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