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Anatomy & embryology of vestibular system

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Vestibular System
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Anatomy & embryology of vestibular system

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

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

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Anatomy & embryology of vestibular system

  1. 1. S Pandey
  2. 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. 3. EMBRYOLOGY
  4. 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. 5. The Semicircular Canals
  6. 6. UTRICLE & SACCULE
  7. 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. 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. 9. Vestibular hair cells  Type 1 & 2  Sensory cells  Stereocilia  Kinocilium  Supporting cells
  10. 10. BLOOD SUPPLY
  11. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 24. Origins of the Cranial Nerves Good to know PLAY
  25. 25. Origins of the Cranial Nerves PLAY Good to know

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