The vestibular apparatus in the inner ear detects sensations of equilibrium and balance. It consists of semicircular canals and otolith organs. The semicircular canals detect rotational movement and contain cristae that bend hair cells when the head rotates. The otolith organs, the utricle and saccule, contain maculae that sense linear acceleration like gravity. Hair cells in both organs release neurotransmitters at different rates depending on the direction and amount of bending, enabling detection of movement and position. Together with other sensory inputs, the vestibular apparatus helps maintain equilibrium and anticipates falls.

1. Vestibular Sensation &
Maintenance of Equilibrium
Dr. Sara Sadiq
(MBBS, M.Phil)

3. Vestibular Apparatus
• It is part of inner ear or labyrinth
• It is a sensory organ that detects sensation of equilibrium
• The other part of labyrinth is the cochlea, which is concerned
with sensation of hearing

4. Labyrinth
Labyrinth or inner ear consists of two structure:
1. Bony Labyrinth
It is composed of a system of bony tubes and chambers located in the
petrous portion of the temporal bone
2. Membranous Labyrinth
It is composed of a system of membranous tubes and chambers

7. Membranous Labyrinth
• It is formed by membranous tubules and sacs.
• Tubules are semicircular canals & sacs are vestibular duct.
• The vestibular duct consists of otolith organ.
• Otolith organ is formed is formed by utricle and saccule.
• The membranous labyrinth is filled with a fluid called endolymph. The
endolymph is similar to ICF in composition.

10. 1. Semicircular Canal
• The three semi-circular canals in each vestibular apparatus, are
placed at right angles to each other.
• Because of this type of arrangement, the semicircular canals
represent the three axes of rotation: vertical, anteroposterior and
transverse axes

11. • The semicircular canals are named according to the situation as
follows:
1. Anterior or superior canal
2. Posterior canal
3. Lateral or horizontal
• The anterior and posterior canals are situated vertically and the
lateral canal is situated in horizontal plane.

14. • When the head is bent forward about 30 degrees, the lateral
semicircular canals are then approximately horizontal with respect to
the surface of the earth
• The anterior canals are in vertical planes that project forward and 45
degrees outward, whereas the posterior canals are also in vertical
planes but project backward and 45 degrees outward.

16. Ampulla
• Among the two ends of
semicircular canal , one end is
narrow and other end is
enlarged.
• The enlarged end is called
ampulla.

17. Crista Ampullaris
• Receptor organ in semicircular canal
• It is a crest like structure situated inside the ampulla
• The crest is formed by a neuroepithelium which consists of hair cells

18. Cupula
• From crista ampullaris, a
dome-shaped gelatinous
structure extends up to the
roof of the ampulla.
• The cilia of hair cells are
projected in the cupula.

21. 2. Otolith Organ  Utricle & Saccule
Macula:
• The receptor organs in utricle and saccule are called maculae.
• Like crista ampullaris it is also formed by neuroepithelium
• Cilia of hair cells are embedded in a gelatinous cap

23. Function of Otolith Organ
• The otolith organs sense linear acceleration
• The saccule senses acceleration in the sagittal vertical plane: up and
down (so it senses gravity) and forward and backward.
• The utricle senses acceleration in the horizontal plane

24. Hair Cell Responses
• In the absence of stimulation, hair cells release neurotransmitter at a
constant rate.
• When hair cell bundles bend:
• Bending toward kinocilia  depolarization
• Bending away from kinocilia  hyperpolarization

29. Predictive Function of Semicircular duct
• Person running forward and suddenly turn to one side
• Semicircular duct already detected that person will fall off balance
• Anticipatory correction is made

30. Factors Concerned With Equilibrium
• Neck Proprioceptors  joint receptors
• Body Proprioceptors  weight effects on footpads
• Exterioceptive information  air pressure during running
• Visual information

31. Neuronal Connection of Vestibular Apparatus

33. Thank You