Physiology of equilibrium & balance

1. Physiology of BodyPhysiology of Body
EquilibriumEquilibrium & & Balance
SYED TOUSIF AHMED

2. Centre of gravity
To balance the centre of gravity
must be above the support point.

3. Physiology Of Body Physiology Of Body Balance

4. Physiology Of BodyPhysiology Of Body Balance

5. BalanceBalance:
BalanceBalance: ability to control equilibrium
•Foot position affects standing balance
– Is defined as :Is defined as :
–““THE ABILITY TO MAINTAIN THE THE ABILITY TO MAINTAIN THE
EQUILIBRIUM OF THE BODY.”EQUILIBRIUM OF THE BODY.”

6. EquilibriumEquilibrium
oIs defined asIs defined as : :
•Physics. The state of a body or physical
system at rest or in un accelerated motion in
which the resultant of all forces acting on it is
zero and the sum of all torques about any axis
is zero.
•There are 2 types of balance
»Static -
»Dynamic –

7. BALANCE
Anticipatory
Mechanisms
(internal)
Proactive
Mechanisms
(external)
Reactive
Mechanisms
Sensory
Systems
Body
Schema
Neuro-
muscular
Synergies
Musculo-
skeletal
Components

8. Balance and Orientation Pathways

9. CNSCNS
1- Cerebral cortex
2- Brainstem
3- Cerebellum
Vestibular -2
Proprioceptive -3
-1visualvisual
Muscle commands
-1
-2
Systems regulating body balance
•Humans use three systems:

10. The Cerebellum
•11% of brain mass
•Dorsal to the pons and medulla
•Controls fine movement coordination
•Balance and equilibrium
•Muscle tone

11. Anatomy of the Cerebellum
•Two hemispheres connected by vermis
•Each hemisphere has three lobes
–Anterior, posterior, and flocculonodular
•Folia—transversely oriented gyri
•Arbor vitae—distinctive treelike pattern of
the cerebellar white matter

12. Figure 12.17b
(b)
Medulla
oblongata
Flocculonodular
lobe
Choroid
plexus of
fourth
ventricle
Posterior
lobe
Arbor
vitae
Cerebellar cortex
Anterior lobe
Cerebellar
peduncles
• Superior
• Middle
• Inferior

13. Cerebellum
Cortico
cerebellum
Vestibulo
cerebellum
Spinocerebellum

14. Vestibulocerebellum
• controls tone & movements of muscles involved
in equilibrium & posture, by receiving impulses
from vestibular apparatus.

15. Spinocerebellum
•coordinates mainly movements of distal parts of
limbs, such as the fast ballistic movements (in
association with cerebrocerebellum), & also
coordinates saccadic eye movements. It
receives impulses from proprioceptors in
muscles, tendons & joints, tactile receptors,
visual receptors & auditory receptors.

16. Corticocerebellum
• coordinates timing & planning involved in fast
sequential movements like writing, running,
talking etc. It perform its function by the intensive
to & fro connection with the cerebral cortex
(cerebro-cerebello-cerebral connections)

18. Granule cell axons ascend to the molecular layer, bifurcate and form
parallel fibers that run parallel to folia forming excitatory synapses on
Purkinje cell dendrites.
Cerebellar cortex also has several types of inhibitory interneurons:
basket cells, Golgi cells, and stellate cells.
Purkinje cell axon is only output of cerebellar cortex, is inhibitory
and projects to the deep nuclei
and vestibular nuclei.
Deep nuclei axons are the
most common outputs of the
cerebellum (excitatory).

19. Cerebellar Cortical Circuits

21. Cerebellar Output Pathways
Lesions of lateral cerebellum affect distal limb coordination.
Medial lesions affect mainly trunk control, posture, balance, and gait.
Cerebellar deficits occur ipsilateral to the lesion because cerebellar
outputs go to the contralateral side and then motor pathways
decussate back to the original side (“double cross-over”).
Vermis lesions do not cause unilateral deficits because medial muscle
groups typically receive bilateral UMN inputs.

22. Static EquilibriumStatic Equilibrium
1) keep the body in a desired position1) keep the body in a desired position,
Static equilibrium –The equilibrium is maintained in a The equilibrium is maintained in a FIXED POSITIONFIXED POSITION, ,
usually while stood on oneusually while stood on one foot.
maintenance of body posture relative to gravity while the body is still.maintenance of body posture relative to gravity while the body is still.

23. Dynamic EquilibriumDynamic Equilibrium
2) move the body in a controlled way
.
Dynamic equilibriumDynamic equilibrium The equilibrium must be maintained The equilibrium must be maintained while performing a while performing a
tasktask which involves MOVEMENT e.g. Walking the beam. which involves MOVEMENT e.g. Walking the beam. – maintenance of the – maintenance of the
body posture (mainly the head) in response to sudden movements. Tracking a body posture (mainly the head) in response to sudden movements. Tracking a
moving object.moving object.

24. Vestibular ReflexesVestibular Reflexes
•Vestibulo-cervical:
–Helps to maintain stability of the head
during movement of the torso.

25. The vestibular labyrinthThe vestibular labyrinth

26. The Vestibular ApparatusThe Vestibular Apparatus
ComponentsComponents
b.b.Three semicircular canals (SCCs)Three semicircular canals (SCCs)
AnteriorAnterior
PosteriorPosterior
 LateralLateral
c.c.Utricle and SacculeUtricle and Saccule
d.d.Vestibular nerve and nucleiVestibular nerve and nuclei

27. •there are five receptor organs housed in each of the
two vestibular labyrinths:
•hair cells in the utricle
•hair cells in the saccule
•hair cells in the anterior vertical semicircular canal
•hair cells in the horizontal semicircular canal
•hair cells in the posterior vertical semicircular canal
® the displacement of hair cells – due to the forces of
gravity and inertia – transduce mechanical stimuli into
receptor potentials
Detect linear accelerations along any axis
Detect
angular
accelerations
about any axis
Vestibular receptorsVestibular receptors

28. Mechanism of Stimulation
Deflection of stereocilia towards kinocilium =Stimulation
Deflection of stereocilia away from kinocilium = Inhibition
Stimulus to the vestibular Stimulus to the vestibular
sensory organssensory organs

29. Vestibular receptorsVestibular receptors

30. Static EquilibriumStatic Equilibrium
Inside the vestibule are two chambers :
utricle and saccule.
Regions of hair cells and supporting cells
called maculae.
Otoliths – “ear rocks”

31. The Utricle and SacculeThe Utricle and Saccule
•Present in the vestibule of the labyrinthPresent in the vestibule of the labyrinth
•Utricle is vertically orientedUtricle is vertically oriented
•Saccule is horizontally orientedSaccule is horizontally oriented
•Sensory hair cells are embedded in the Sensory hair cells are embedded in the
maculae of the utricle and sacculemaculae of the utricle and saccule
•Hair cells are covered by a membrane called Hair cells are covered by a membrane called
otolithic membraneotolithic membrane

32. MaculaeMaculae

33. The Semicircular CanalsThe Semicircular Canals
1.Fluid filled
2.Each canal has a dilated end = Ampulla
3.The ampulla houses the sensory hair cells
which are covered by a gelatinous material
a.Ampulla
aCristae = hair cells
eCupulae = gelatinous material

34. the vestibular labyrinththe vestibular labyrinth
Anterior
Lateral
Posterior

35. Otolithic
membrane
Hair cell
Anatomy: Maculae of Utricle or Saccule
Physiology: Linear acceleration of head

36. •the vestibulo-ocular reflex is an example of a
reflexive eye movement that exists between
semicircular canals and nuclei controlling extrinsic eye
muscles
Vestibular pathwaysVestibular pathways

38. Vestibulo-Ocular Reflex (VOR)Vestibulo-Ocular Reflex (VOR)
STIMULUS =
Head movement
Efferent = oculomotor nerves
Effector =Extra-ocular muscles
= Sensory
Vestibular HC
Afferent =vestibular nerve
Center
Vestibulo-ocular
Helps maintain stability of visual field
Leads to physiologic nystagmus

39. •1
st
order sensory neurons:
-dendrites surround base of hair cells in vestibule and
semicircular canals
-cell bodies located in the vestibular ganglion
-the vestibular ganglion lies in a swelling of the vestibular
nerve within the internal auditory meatus
-about 20,000 axons join to form vestibular nerve, which
joins cochlear nerve to form vestibulocochlear nerve
-vestibular nerve portion projects to the ipsilateral
complex of four major vestibular nuclei in the dorsal
part of the pons and medulla
-axons of 1
st
order sensory neurons synapses with 2
nd
order sensory neurons (interneurons) in the vestibular
nuclei
Vestibular pathwaysVestibular pathways

40. Vestibular pathwaysVestibular pathways

41. •2
nd
order sensory
neurons in vestibular
nuclei
-integrate signals from vestibular
organs with those from
ospinal cord
ocerebellum
ovisual system
-project to 3
rd
order sensory
neurons in
othe ventral nuclei of the
thalamus
ooculomotor nuclei
oreticular centers occupied with
skeletal movement
ospinal centers occupied with
skeletal movement
ovestibulocerebellum
Vestibular pathwaysVestibular pathways

42. •3
rd
order sensory
neurons
•in the ventral thalamus send
axons to synapse with
neurons in vestibular area
(Brodmann’s area 2V and
3a) of the primary
somatosensory cortex
-the cortex uses the
information from the
vestibular apparatus
(acceleration and angular
rotation) to generate a
subjective measure of self-
movement and the external
world
Vestibular processing areasVestibular processing areas

43. THE END