The document summarizes the vestibular system which is involved in maintaining equilibrium and balance. It describes the three main systems - vestibular, visual, and proprioceptive. The vestibular system contains the semicircular canals and otolith organs which detect head movement and gravity. The hair cells in each organ bend to detect rotational or linear acceleration and send signals to the brain. Disorders like nystagmus and vertigo can result from vestibular problems. Together, the three systems allow the brain to integrate sensory information and coordinate muscle movements to keep the body balanced.

1. Equilibrium
Dr. KJG,
PROFESSOR,
DEPT. OF PHYSIOLOGY,
MGMC & RI

2. Objectives
• Structure – nuclei, connections, functions and
disorders of the vestibular apparatus.

3. Systems involved in Equilibrium
• The main systems that are involved in
equilibrium are:
The Vestibular System
The Visual System
The Proprioceptive System
Cerebellum

7. Vestibular apparatus
• The receptor organs for equilibrium are
collectively called the vestibular apparatus
• Has a role in regulation of posture &
equilibrium
• Complex sense organ which is stimulated by
– Gravity
– Rotation movements

8. Location & parts
• The vestibular apparatus is present in
inner ear & comprises of
• 3 semi-circular canals
• Otolith organs
– The utricle
– The saccule

9. Types of Equilibrium
Rotational
movement
Static equilibrium =
Maintenance of position of the
body (head) relative to force of
gravity
Dynamic equilibrium =
Maintenance of body position
(head) in response to rotational
movements

10. Static Equilibrium
• Receptors for static equilibrium are the
Maculae.
• Maculae present in Saccule & Utricle
(otolith organs)

11. Macula
● Each macula contains supporting cells and
scattered receptors called hair cells
• Each of the hair cells has a major ciliary process
called kinocilium and several smaller stereocilia
• Lying over the supporting and hair cells is the
gelatin-like otolithic membrane
• The otolithic membrane contains the otoliths
(calcium carbonate crystals) on their surface
• The base of the hair cells are innervated by
branches of the vestibular branch of VIII nerve

12. 1- Supporting cells 4- Otolith membrane
2- Hair cell 5- nerve fibers
3- Cilia 6- Otoliths

14. • The Maculae detect linear
acceleration forces.
• The Maculae in the-
Saccule:
Responsible for
vertical acceleration
Utricle:
Responsible for
horizontal acceleration
Saccule
Utricle
Maculae in Saccule & utricle

15. STATIC EQUILIBRIUM
Gravity, linear acceleration, or linear
deceleration pull the otoliths & otolithic
membrane resulting in
bending of stereocilia towards kinocilium 
leads to generation of nerve impulses carried
by vestibular branch of vestibulocochlear (VIII)
nerve

16. Linear Acceleration
• When the hair bends
towards the kinocilium
the hair cell depolarize
Faster stream of impulse
is sent to the brain
• When the hair bends in
the opposite direction the
hair cells hyperpolarize
Slower impulse
generation

17. The maculae respond to gravitational pull and help to
maintain static equilibrium

18. Macula in Utricule
K

19. Macula in Saccule
K

20. Functions of otolith organs
• Give information about static position of
head
• Activate appropriate mechanisms to
maintain an equilibrium during resting &
linear movements

21. DYNAMIC EQUILIBRIUM
Maintenance of body position (head) in
response to rotational movements
Subserved by the hair cells present in
the semicircular canals (SCC)

22. The 3 SCCs are oriented
at right angles to one
another
1. Anterior & posterior
semicircular canals
(positioned vertically)
3. Lateral semicircular
canal
(positioned horizontally)
SCCs are filled with
endolymph

23. Semicircular Canals
• Respond to angular acceleration in the
plane of the canal.
• Are functionally paired:

24. Ampulla
• Each SCC has a
dilated end called
ampulla containing
receptor organ crista
ampullaris (small
elevation)
• Each crista contains
hair cells and
supporting cells
covered by cupula
(gelatinous material)
Cupula
Cristae

25. The orientation of 3 canals permit detection of
rotational acceleration (dynamic equilibrium)

26. Macula in SSC
K K
Left side Right side

28. • Rotational acceleration or deceleration
of head causes endolymph to flow over
the hairs and bend them  results in
nerve impulses being carried away by
vestibular branch of vestibulo cochear
nerve

29. Mechanism of Stimulation in SCCs
1- Angular acceleration of head
2- Motion of fluid in opposite
direction in SCC
3- Pressure on cupula of SCC
4- Deflection of stereocilia to /
away from kinocilium
5 - ↑/↓ K+ influx into hair cells
6- Increase/decrease firing rate
K

30. The cristae respond to rotational movements and are
involved in dynamic equilibrium

31. Functions of semicircular canals
• Give information about rotation movements
of the head & activate appropriate
mechanisms to maintain an equilibrium
• Helps in visual fixation during angular
rotation of head through vestibulo – ocular
reflex

32. Connections of vestibular apparatus
Vestibulo cerebellum
VCT fibers
Spinal cord III, IV & VI Cranial N. nuclei
VST fibers MLB
Integrate labyrinthine reflexes
Otolith organs
Semicircular canal
Vestibular nucleus

35. Vestibulo-Ocular Reflex (VOR)
STIMULUS =
Head movement
Efferent = oculomotor nerves
Effector = Extra-ocular muscles
Sensory =
Vestibular HC
Afferent = vestibular nerve
Center

36. Vestibulo-Spinal Reflex (VSR)
STIMULUS =
Gravity linear acceleration
Efferent = Spinal nerves
Effector = Neck and body muscles
Sensory =
Vestibular HC
Afferent = vestibular nerve
Center

37. The Visual System
• 2nd system that plays an important role in
equilibrium
• The effect of the visual system is best
noticed when there is a conflict between the
messages that reach the brain.
• Motion sickness is a very common
equilibrium disorder in which is due to
sensory input mismatch. The main
symptoms are: Nausea, dizziness, vomiting
and pale appearance

38. Motion sickness
Example -
– When we read while traveling, the visual
inputs indicates that the body is fixed. But
as the vehicle is moving the vestibular
system detects movement and send
impulses that conflict with the visual
system.
– The brain receives conflicting information
which will lead to motion sickness.

39. Propreceptive system
• Nerve endings that respond to muscle and
tendon stretch are called proprioceptors (ex.
Muscle spindle). They send signals to the
brain, giving it information about the posture
of the body.
• The proprioceptors are available in the
muscles, ligaments, tendons, and joints. It
which they can detect the initiation and
termination of body movement.
• Note: In a sitting situation the system that is
responsible for equilibrium in the
PRORIORECEPTOR

40. Vestibular apparatus - Summary
• Plays an important part in regulation of
posture
• Otolith organ
i) Reflexly maintains upright position of
head and
ii) Adjusts position of the body to that of
head in space or relative to the trunk
“Equilibrator of the head”

41. CNS
1- Cerebral cortex
2- Brainstem
3- Cerebellum
2- Vestibular
3- Proprioceptive
1-
Muscle commands
1-
2-
Systems regulating Posture

42. Applied aspects
Disorders of vestibular apparatus
• Nystagmus
• Vertigo
• Travelling sickness, sea sickness
• Meniere’s disease : vertigo, tinnitus & hard
of hearing

43. Nystagmus
Involuntary movement of eyeball
•Reflex which helps in visual fixation while the
body rotates
•Recorded by electronystagmograpy

44. • Normally, right vestibule tends to deviate the eyes
to the left & vice versa.
• With normal tone two effects are cancelled & the
eyes remain in mid position.
• If the right vestibule is destroyed, the normal tone
exerted by the left side pushes the eye to the right.
This is corrected to the central position with a quick
movement. So there is nystagmus to the left
(normal side)
• If the right vestibule is hyperactive, nystagmus to
the right occurs
• Nystagmus also produced in cerebellar disease

45. Electronystagmogram
• Utilizes charge
difference
between retina
and cornea to
detect eye
movement

46. Tests
• Caloric test
• Barany’s test

47. spin student safely
for 10 turns
halt student,
closely observe eyes
Barany’s test

48. Thank you