This powerpoint elaborates the mechanism of balance & anatomy of vestibular apparutus. It also depicts the anatomy & physiology of haircells in detail. I also explained the vestibular function tests used for diagnosis of various vestibular disorders.

1. Mechanism Of Balance
By
Dr. Utkal Mishra

2. Introduction
 The main function of the mammalian vestibular system
is to
 Provide general orientation of the body with respect to gravity
 Enable balanced locomotion and body position
 Readjust autonomic functions after body reorientation
 Ensure gaze stabilization.

3. Introduction

4. Physiology of equilibrium
Balance of body during static or dynamic positions is
maintained by 4 organs:
1. Vestibular apparatus
2. Eye
3. Posterior column of spinal cord
4. Cerebellum

5. Vestibular apparatus
 Semicircular canals - Angular acceleration & deceleration
 Utricle - Horizontal linear acceleration & deceleration
 Saccule - Vertical linear acceleration & deceleration

6. Relevant Anatomy

7. Orientation of semicircular canals
RALP PlaneLARP Plane

8. Motion Decomposition
 Every motion in space can be broken
down into
 3 Rotational
degrees of freedom – 1. Yaw
(SCC) 2. Pitch
3. Roll
 3 Translational
degrees of freedom – 1. Left–Right
(U & S) 2. Up–Down
3. For–Aft

9. Physiology of head movement
HEAD MOVEMENT SEMICIRCULAR CANAL
STIMULATED
YAW LATERAL
PITCH POSTERIOR + SUPERIOR
ROLL SUPERIOR + POSTERIOR

10. Cristae
 Location – Ampullated ends of 3
SCC.
 Elevated sensory area containing
sensory hair cells
 Tips of cilia are embedded in a
gelatinous mass composed of
polysaccharide called – CUPULA
 Cupula functions as a water tight
partition & displacement occurs in
one direction at a time as a swing
door.

11. Macula
 Located in utricle – floor (horizontal)
& saccule – posterior wall (vertical)
 The hair cells are embedded in a gelatinous
layer impregnated with crystals of CaCO3
called OTOLITH MEMBRANE.
 A filamentous network connects the lower
surface of otolithic membrane with sensory
epithelium called SUBCUPULAR
MESHWORK .
 A virtual curved line called STRIOLA
divides utricular hair cells into medial &
lateral groups
& sacuular hair cells into ventral & dorsal
groups with opposite orientation

12. Vestibular Sensory Cells
 Vestibular sensory epithelium consists of 2 types
of hair cells –
TYPE 1 – Flask shaped sorrounded by cup shaped
thick myelinated single afferent nerve terminal
TYPE 2 – Cylindrical with multiple thin afferent
nerve terminals at its base
 The apex of hair cells is bathed in endolymph
and is sorrounded by nonsensory supporting
cells & dark cells.

13. Hair Cells
 Hair cell consists of a hair bundle
at the apical end.
 Each HAIR BUNDLE consists
of 1 large knobed
KINOCILLIUM & 20 - 300
STEREOCILLIA

14. Stereocillia
 Have a cytoskeleton made up of actin
filament crosslinked by fibrin
 Arranged in a HEXAGONAL
configuration
 With shortest steriocillia at one end &
tallest at other end like a staircase.
 The ion channel involved in
mechanoelectrical transduction are
located in steriocillia.
 Connected to each other by fibrillary
strands called TIP LINKS
 The upper end of each tip link is anchored
to the stereocilium at a point called
INSERTIONAL PLATE or PLAQUE.
 Tension in the tip link controls the
opening or closing of the ion channels.

15. Kinocillium
 It is a true cillium consisting of an axoneme (9+2).
 Only function of kinocillium is - transmission of stimulus forces
to stereocillia.
 Displacement of stereocillia towards kinocillium causes
depolarization.

16. Hair Cell Physiology

17. Mechanotransduction
Displacement of stereocillia
towards kinocillium
Stretches Tip links
Influx of K+ & Ca+
Depolarization

18. Gating Compliance
 An intrinsic property of direct mechano-
electrical transduction that enhances hair
cell sensitivity.
 Hair bundle displacement in the positive
direction opens transduction channels.
 Channel opening decreases the stiffness of
the hair bundle
 This in turn promotes further movement
in a positive direction resulting in a
positive feedback mechanism

19. Adaptation
 It prevents saturation of mechano-transductor response from large
sustained stimuli > 25ms.
 It also allows a cell to detect small stimuli in the presence of an
enormous background input.
 2 distinct models of adaptation –
 Active Motor Model
 Calcium Dependent Closure Model

20. Active Motor Model Myosin 1b
Hair bundle deflection towards kinocilium
increases tension in tip links with opening of
transduction channels
DEPOLARIZATION
Motor cannot resist the increased tension
& slips down the stereocillium
Tip link tension reduced & channels closed
HYPERPOLARIZATION
Stereocillia returns to resting stage

21. Calcium Dependent Closure Model
Opening of
transduction
channel
Calcium enters &
binds to channel
protein
Closure of channel

22. Vestibulo-Ocular Reflex
• It is a reflex eye movement due to stimulation of cristae of SCC during head
rotation
• It helps in Gaze Stabilization by producing eye movements in the direction
opposite to head movement, thus preserving the image on the fovea.
• Movement of head to left  left horizontal canal stimulated & right
horizontal canal inhibited
• To keep eyes fixed on a stationary point, both eyes move to right side by
stimulating right lateral rectus & left medial rectus muscles.

23. Principle Of VOR Generation (PUSH- PULL)
HEAD ROTATION TO LEFT
STIMULATES LEFT HORZ. CANAL
SIGNAL GOES TO MVN
AXONS DECUSSATE TO
CONTRALATERAL ABDUCENS
NUCLEUS
RT. LATR. RECTUS CONTRACTION
INTERNEURONS FROM RT. ABDUCENS
NUCLEUS AGAIN CROSSES TO LEFT BY
MLF & PROJECTS TO LEFT
OCCULOMOTOR NUCLEUS
LEFT MEDIAL RECTUS
CONTRACTION
HYPERPOLARIZATION OF
RIGHT SCC
RELAXATION OF LEFT
LATERAL RECTUS & RIGHT
MEDIAL RECTUS
PUSH
PULL
Right

24. Vestibulospinal reflex
 Effector organs - Extensor muscles of neck, trunk, arms and
limbs.
 The driving input here is mainly Gravity detected by the otolith
system.
 These reflexes are mediated through projections of the vestibular
nuclei on to the Medial and Lateral Vestibulospinal tract.
 Similar to the VOR, the same push–pull mechanisms are used for
controlling the balance between extensor and flexor muscles.

25. Cervicoocular reflex
 When the head is fixed but the body is rotated, nystagmus may
be observed.
 This reflex is based on the stimulation of neck receptors.
 In humans, this reflex is very unreliable and unpredictable
 Only in subjects with congenital peripheral vestibular loss, does
this alternative strategy for gaze stabilization become helpful.

26. Central Projections Of Vestibular System
 In the brain stem there are 4 vestibular nuclei
 Superior
 Lateral
 Medial
 Descending
 From there several projections are found to
 Occulomotor Nuclei
 Lateral & Medial Vestibulospinal Tract
 Parapontine Reticular Formation
 Vestibulocerebellum- Floculus, Nodulus
 Nucleus Tractus Solitarius
 Cingulate Gyrus

27. VESTIBULAR FUNCTION
TESTS
Dr Utkal Mishra

28. Vestibular Function Tests
 Assessment of vestibular function can be divided
into 2 groups –
 1. CLINICAL TESTS
 2. LABORATORY TESTS

29. Clinical Tests Of Vestibular Function
 1. Clinical examination of eye movements
 2. Fistula Test
 3. Romberg Test
 4. Gait
 5. Tests Of Cerebellar Dysfunction

30. Clinical Examination of Eye Movements
The oculomotor examination should include:
 Nystagmus
 Convergence;
 Smooth pursuit;
 Saccades;
 Vestibulo-ocular reflexes;
 Positional manoeuvres.

31. Nystagmus
 It is defined as involuntary rhythmic oscillatory movement of
eyes.
 Described under headings –
1. Plane – Horizontal, Vertical, Torsional
2. Waveform – Saw tooth / Jerk – Contains a fast &
slow phase
Pendular- Quasisinusoidal
No fast or slow phase
3. Direction – Indicated by direction of fast component
4. Intensity – ALEXANDERS LAW
1st degree – Nystagmus present when looks in
direction of fast component.
2nd degree - Nystagmus present when looks
straight ahead.
3rd degree – Nystagmus present when looks in
direction of slow component.

32. Types of Nystagmus
DIFFERENCE
Peripheral Central
Latency 2-20 s No latency
Duration < 1 min > 1 min
Direction Direction fixed Direction changing
Fatiguability Fatiguable Non fatiguable
Symptoms Severe Vertigo None
Suppressed by Visual fixation None
Enhanced by Darkness or by using
Frenzel’s glasses
None
 Vestibular nystagmus is of 2 types
 Peripheral - Due to lesions of Labyrinth or VIIIth Nerve.
 Central – Due to lesions of Vestibular Nuclei, Brain stem, Cerebellum.

33. Central Nystagmus
Type of Nystagmus Cause Remarks
Pendular Nystagmus Multiple Sclerosis Can be disconjugate – vertical
in one eye & horizontal in other
eye.
Purely Torsional Syringomyelia
Vertical Downbeat Arnold Chiari Malformation
Vertical Upbeat Pontomedullary juncn. lesions
Congenital Nystagmus Jerk Nystagmus with slow
phase velocity exponentially
increasing.
Seasaw Nystagmus Mid-brain lesions One eye goes up other goes
down
Dissociated Nystagmus Internuclear Opthalmoplegia Only abducting eye shows
nystagmus
Periodic Alternating
Nystagmus
Lesions in Nodulus of
Cerebellum
Changes direction every 2
minutes
Perverted Nystagmus Multiple Sclerosis Nystagmus occuring in a a
plane other than that of
vestibular stimulation.

34. Vestibulo-Occular Reflex
 VOR stabilizes gaze in space during head movements
 By generating slow phase eye movements of an equal velocity but in
opposite direction to head movement.
 Clinical Tests for VOR are –
1. Doll’s Head Manoeuvre
2. Dynamic Visual Acuity
3. Head Impulse Test

35. Doll’s Head Manoeuvre
Examiner oscillates the patients head from side
to side at a frequency of approx. 0.5-1Hz.
Maintain fixation
(Normal VOR)
Interrupted Eye movements with catch up
saccades towards fixation target
(Abnormal VOR)
Post Meningitis / Ototoxicity
Patient sits in front of examiner &
fixates a part of examiners face(nose)

36. Dynamic Visual Acuity
Patient reads a visual acuity chart
6/6
Standing behind the patient
Examiner oscillates the patient’s head
at approx. 1Hz. While a new visual
acuity is taken
Gross reduction of VOR
Deterioration of Two linesNo change in Visual Acuity
NORMAL

37. Head Impulse Test
Patient seats in front of Examiner
& fixate a target across the room
Head is turned briskly by 15 degree
across midline by the examiner
Fixation maintained
NORMAL
Acute Vestibular Neuronitis
Eyes moves with head &
refixate with catch up saccades.

38. Positional Manoeuvre (Hallpike)
Patient sits on a couch & looks straight ahead
at one point on the examiner’s face
Examiner holds the patient head & turns it 450 to right
Patient placed in supine position with head
hangs 300 below horizontal
Patient eyes are observed for nystagmus for minimum 20 sec
Nystagmus appearing after a latent period of 2-20 s
Last for < 1 min & is always in one direction
On subsequent repetitions nystagmus disappears
(Fatiguable)
Nystagmus appearing immediately,
changing direction & non fatiguable
BPPV
CENTRAL
LESIONS

39. Fistula test
 Intermittent pressure on tragus induces nystagmus by pressure changes in
EAC which is transmitted to labyrinth.
 Results - Negative  Normal
Positive  Erosion of Horz. SCC
 Fenestration Operation
 Post-Stapedectomy Fistula
 Rupture of round window
False Negative  Cholesteatoma covering the
fistula
 Dead Labyrinth
False Positive  Hypermobile stapes
(Congenital Syphilis)
 Stapes connected to Utricular
macula by fibrous bands
(Meniere’s disease)

40. Romberg’s Test
Sways to the side of lesion
(Peripheral Lesion)
Shows instability
(Central Lesion)
No sway or instability
Sharpened Romberg’s Test
Pt. stands with one heel in
front of toes & arms folded
across the chest
Patient stands with feet
together & arms by the side
with eyes open then closed

41. Unterberger’s Test
Turns towards the
Hypoactive side
(Peripheral Lesion)
Shows instability
(Central Lesion)
Patient asked to walk on the spot with eyes
closed & keeping the arm & index fingers
pointing towards examiners index fingers

42. Gait
Sways to the side of lesion
(Peripheral Lesion)
Shows instability
(Central Lesion)
Paradoxical Improvement with
fast walking
Acute Vestibular Neuronitis
Patient is asked to walk along a straight line
to a fixed point, first with eyes open then
closed

43. Tests of Cerebellar Dysfunction
DISEASE OF SIGNS
CEREBELLAR HEMISPHERE  Asynergia
 Dysmetria
 Adiadochokinesia
 Rebound Phenomenon
MIDLINE OF CEREBELLUM  Wide base Gait
 Falling in any direction
 Inability to make sudden turns while walking
 Truncal ataxia

44. Laboratory Tests of Vestibular Function
 Caloric Test
 Modified Kobrak Test
 Fitzgerald-Hallpike Test
 Cold Air Caloric Test
 Electronystagmography
 Optokinetic Test
 Rotation Test
 Galvanic Test
 Posturography

45. Caloric Test
 Principle- Changes in temperature in Extn. Auditory canal induces
convection currents in endolymph of Lateral SCC causing vertigo &
nystagmus
 Advantage – Only test available to test each labyrinth separately.
 Disadvantage – Anatomic abnormality of Extn. Or Middle ear interfere with
results
 Types – 3 types
 1. Modified Kobrak Test
 2. Fitzgerald-Hallpike Test
 3. Cold Air Caloric Test

46. Modified Kobrak Test
Patient is seated with head tilted 600 backwards
(Horz. Canal in vertical position)
Ear irrigated with ice water for 60 sec
Start with 5ml NO RESPONSE
Nystagmus beating towards opposite ear 10 ml
NORMAL
20 ml
40 ml
DEAD
LABYRINTH

47. Fitzgerald- Hallpike Test
Patient lies supine with head tilted 300 forward
(Horz. Canal in vertical position)
Procedure follows order
LEFT COLD>>RIGHT COLD>>LEFTWARM>>RIGHT WARM
Gap of 5 minutes
Cold water induces nystagmus to opposite side
& warm water to same side of irrigation
Time taken from the start of irrigation to end of
nystagmus recorded in a chart called
CALORIGRAM
Irrigation for 4 min with
water at 200C
Ear is irrigated for 40 sec alternately with water at 300C &
440 C
NO RESPONSE
NO RESPONSE
DEAD LABYRINTH

48. Cold Air Caloric Test
 It is done when there is Tympanic membrane
perforation.
 Test is done with Dundas – Grant tube which
is a coiled copper tube wrapped in cloth.
 Air in the tube is cooled by pouring ethyl
chloride & blown into ear
 This is only a rough qualitative test.

49. Interpretations of Caloric Test
 There are 3 main abnormalities of caloric response-
 1. Bilateral Absence of Caloric Response
 2. Unilateral Canal Paresis
 3. Directional Preponderance

50. Bilateral Absence of Caloric Nystagmus
 Occurs in –
 Post- Meningitis
 Ototoxic drugs
 Meniere’s Disease
 Head Trauma
 Idiopathic

51. Unilateral Canal Paresis
 It indicates a reduced or absent response from one ear.
 Causes are –
 Acoustic neuroma
 Post labyrinthectomy
 Vestibular nerve section
 Can be expressed as percentage as
Response from Left ear =
L30 + L44 × 100
L30 + L44 + R30 + R44

52. Directional Preponderance
 It indicates that the Duration of nystagmus to one side is 25-30%
more than other side irrespective of whether it is elicited from
right or left labyrinth.
 DP occurs towards the side of central lesion &
away from the side of peripheral lesion
 Right beating nystagmus =
L30 + R44
L30 + L44 + R30 + R44
× 100

53. Electro/Video nystagmography
 It is a method of detecting & recording of
nystagmus.
 It depends on the presence of
corneoretinal potentials recorded by
surface electrodes placed around orbit.
 Advantage –
 1. Detect fine nystagmus not visible to
naked eye
 2. To keep a permanent record
 3. To detect nystagmus in dark.
 Disadvantage –
 1. Cannot record torsional eye
movement
 2. Other biological potentials can be
picked up as artifact (EEG)

54. Optokinetic test
 Patient is asked to follow a series of
vertical stripes on a rotating drum.
 Normally it produces nystagmus with
slow component in the direction of
moving stripes & fast component in
opposite direction.
 Abnormality indicates central lesion.

55. Rotational Tests
 Patient is seated in a Barany’s revolving
chair with head tilted 300 forward
rotated 10 turns in 20 s.
 The chair is stopped abruptly &
nystagmus is observed towards the side
of rotation.
 2 types of rotation-
 Velocity Step/ Impulsive Rotation
 Sinusoidal Rotation
 Normally nystagmus lasts for 25-40s.
 Advantage – Test can be performed in
cases of congenital abnormalities where
SCC failed to develop
 Disadvantage- Both the labyrinths are
simutaneously stimulated.

56. Galvanic Test
 Only test which differentiates an end organ lesion
from that of vestibular nerve.
 Patient stands with his feet together eyes closed &
arms outstretched & then a current of 1mA is passed
to one ear.
 Normally patient sways towards the side of anodal
current. (Intact vestibular nerve)

57. Posturography
 It is a method to evaluate vestibular function by
measuring postural stability.
 2 main types
 Static Posturography- Fixed platform
 Computerized Dynamic Posturography – Movable
platform