The document discusses the anatomy and functions of the vestibular apparatus. It describes the vestibular apparatus as consisting of the semicircular canals, utricle, and saccule located in the inner ear. These contain hair cells that act as receptors and detect head movement and acceleration. When stimulated, the hair cells trigger vestibular pathways that connect to the brainstem and mediate reflexes for eye and body movements to maintain equilibrium and posture. The vestibular apparatus plays an important role in functions such as balance, spatial orientation, and eye movement coordination.

1. DR NILESH KATE
MBBS,MD
PROFESSOR
ESIC MEDICAL COLLEGE, GULBARGA.
DEPT. OF PHYSIOLOGY
VESTIBULAR
APPARATUS

2. OBJECTIVES.
 Functional anatomy
 Vestibular receptors
 Vestibular pathways
 Mechanism of functioning
 Functions
 Maintenance of equilibrium
 Applied aspects.

3. Functional anatomy.
 Internal
ear/labyrinth–
petrous part of
temporal bone
 Consists of
 Bony labyrinth
 Membranous labyrinth.
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4. Bony labyrinth
 3 parts
 Vestibule
 Semicircular canals
 Cochlea
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5. Membranous labyrinth
 In bony labyrinth
 Filled with endolymph.
 Surrounded by perilymph.
 Consists of
 Utricle & saccule – in bony
vestibule
 Semicircular ducts – in
canals
 Ducts of cochlea – in
cochlea
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6. Vestibular apparatus
 Semicircular canals &
utricle & saccule
together called -
Vestibular apparatus
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7. Semicircular canals
 Anterior
 Posterior
 Lateral
 One end of each dilated
– ampulla which
contains receptor organ
– crista ampullaris.
 They open into utricle
by 5 orifices.
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8. Otolith organs
 Utricle & saccules
together called –
Otolith organs.
 Utricle – larger, opens 3
semicircular canals
 Connected to saccules &
endolymphatic sac
 Saccules
 Connected to utricle &
cochlea – ductus reunion.
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9. Vestibular receptors
 Hair cells
 Location – of
semicircular canals in
mass of tissue within
ampulla- crista
ampullaris.
 Of otolith organs in
macula.
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11. Hair cells
 Type I
 Type II
 Cilia of hair cells –
stereocilia.
 Large nonmotile –
kinocilium.
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12. Activity of hair cells
 Rmp – 60 mv
 Steriocilia bend
towards – depolarize
 Away – hyperpolarize.
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13. Receptors in semicircular
canals
 Crista ampullaris.
 Neuroepithelium
 Secretory epithelial
cells
 Cupula.
 Unaffected by linear
acceleration
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15. Receptors in otolith organs
macula
 Structure
 Neuroepithelium
 Supporting cells
 Otolith membrane.
 Contains crystals of Ca
carbonate – otoliths or
otogonia
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16. Stimulation of receptors in
otolith organs.
 Macula of utricle
 Linear acceleration.
 Macula of saccule
 Vertical acceleration.
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17. Vestibular pathways
 First order neurons
 Vestibular nuclei
 Afferents
 Efferents
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18. EFFERENTS
 Vestibulospinal tract
 Vestibulo-ocular
 Vestibulo-cerebellar
 Vestibulo-reticular
 Vestibulo-rubral
 Vestibulo-thalamo-
cortical.
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19. Friday, June 19, 2020

20. Mechanism of functioning
 Mechanism of
stimulation –
 At the beginning of
movements
 At the end of
movements.
 Mechanism of
adaptation. – after
15-20 sec of
continuous movement.
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21. Functions
 Utricle –
 Stimulated during
horizontal acceleration
 Saccules –
 Stimulated during
vertical acceleration
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22. Vestibular reflexes
 Vestibulo-ocular
 Otolith reflexes – prevents leg injuries
during jump.
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23. Vestibulo-ocular
 Nystagmus
 Slow component
 Fast component.
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24. Functions of vestibular
apparatus
 Role in maintenance of equilibrium
 Role in maintenance of posture.
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25. Maintenance of equilibrium
 Otolith organs – linear acceleration
 Semicircular canals – angular acceleration.
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26. Role in maintenance of
posture.
 Vestibular placing reaction
 Righting reflexes
 Vestibulo ocular reflex
 Vestibulo-otolith reflex.
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27. Applied aspects
 Vestibular dysfunction
 Experimental stimulation of semicircular
canals
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28. Vestibular dysfunction
 Motion sickness
 Benign paroxysmal positional vertigo
 Miniere’s disease
 Labyrinthetcomy.
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29. Experimental stimulation of
semicircular canals
 Stimulation of rotational movements by
Barany’s chair
 Calorie stimulation
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30. THANK YOU