Vestibular apparatus

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

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

Functional anatomy.
 Internal
ear/labyrinth–
petrous part of
temporal bone
 Consists of
 Bony labyrinth
 Membranous labyrinth.
Friday, June 19, 2020

Bony labyrinth
 3 parts
 Vestibule
 Semicircular canals
 Cochlea

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

Vestibular apparatus
 Semicircular canals &
utricle & saccule
together called -
Vestibular apparatus

Semicircular canals
 Anterior
 Posterior
 Lateral
 One end of each dilated
– ampulla which
contains receptor organ
– crista ampullaris.
 They open into utricle
by 5 orifices.

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.

Vestibular receptors
 Hair cells
 Location – of
semicircular canals in
mass of tissue within
ampulla- crista
ampullaris.
 Of otolith organs in
macula.

Hair cells
 Type I
 Type II
 Cilia of hair cells –
stereocilia.
 Large nonmotile –
kinocilium.

Activity of hair cells
 Rmp – 60 mv
 Steriocilia bend
towards – depolarize
 Away – hyperpolarize.

Receptors in semicircular
canals
 Crista ampullaris.
 Neuroepithelium
 Secretory epithelial
cells
 Cupula.
 Unaffected by linear
acceleration

Receptors in otolith organs
macula
 Structure
 Neuroepithelium
 Supporting cells
 Otolith membrane.
 Contains crystals of Ca
carbonate – otoliths or
otogonia

Stimulation of receptors in
otolith organs.
 Macula of utricle
 Linear acceleration.
 Macula of saccule
 Vertical acceleration.

Vestibular pathways
 First order neurons
 Vestibular nuclei
 Afferents
 Efferents

EFFERENTS
 Vestibulospinal tract
 Vestibulo-ocular
 Vestibulo-cerebellar
 Vestibulo-reticular
 Vestibulo-rubral
 Vestibulo-thalamo-
cortical.

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.

Functions
 Utricle –
 Stimulated during
horizontal acceleration
 Saccules –
 Stimulated during
vertical acceleration

Vestibular reflexes
 Vestibulo-ocular
 Otolith reflexes – prevents leg injuries
during jump.

Vestibulo-ocular
 Nystagmus
 Slow component
 Fast component.

Functions of vestibular
apparatus
 Role in maintenance of equilibrium
 Role in maintenance of posture.

Maintenance of equilibrium
 Otolith organs – linear acceleration
 Semicircular canals – angular acceleration.

Role in maintenance of
posture.
 Vestibular placing reaction
 Righting reflexes
 Vestibulo ocular reflex
 Vestibulo-otolith reflex.

Applied aspects
 Vestibular dysfunction
 Experimental stimulation of semicircular
canals

Vestibular dysfunction
 Motion sickness
 Benign paroxysmal positional vertigo
 Miniere’s disease
 Labyrinthetcomy.

Experimental stimulation of
semicircular canals
 Stimulation of rotational movements by
Barany’s chair
 Calorie stimulation

Vestibular apparatus

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