Physiology of equilibrium & balance
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Transcript of Physiology of equilibrium & balance
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Physiology of BodyPhysiology of Body EquilibriumEquilibrium & & Balance
SYED TOUSIF AHMED
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Centre of gravity
To balance the centre of gravitymust be above the support point.
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Physiology Of Body Physiology Of Body Balance
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Physiology Of BodyPhysiology Of Body Balance
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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.”
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EquilibriumEquilibriumEquilibriumEquilibrium
o Is 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 –
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BALANCE
Anticipatory Mechanisms
(internal)
Proactive Mechanisms
(external)
ReactiveMechanisms
Sensory Systems
Body Schema
Neuro-muscular Synergies
Musculo-skeletal
Components
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Balance and Orientation Pathways
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CNSCNS1- Cerebral cortex2- Brainstem 3- Cerebellum
2 -Vestibular
3 -Proprioceptive
1 -visualvisualMuscle commands
1-
2-
Systems regulating body balance
•Humans use three systems:
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The Cerebellum
• 11% of brain mass
• Dorsal to the pons and medulla
• Controls fine movement coordination
• Balance and equilibrium
• Muscle tone
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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
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Figure 12.17b
(b)
Medullaoblongata
Flocculonodularlobe
Choroidplexus offourth ventricle
Posteriorlobe
Arborvitae
Cerebellar cortex
Anterior lobe
Cerebellarpeduncles• Superior• Middle• Inferior
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Cerebellum
Cortico cerebellum
Vestibulo cerebellum
Spinocerebellum
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Vestibulocerebellum
• controls tone & movements of muscles involved
in equilibrium & posture, by receiving impulses
from vestibular apparatus.
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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.
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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)
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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).
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Cerebellar Cortical Circuits
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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 pathwaysdecussate back to the original side (“double cross-over”).
Vermis lesions do not cause unilateral deficits because medial musclegroups typically receive bilateral UMN inputs.
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Static EquilibriumStatic Equilibrium 1) keep the body in a desired position1) keep the body in a desired position,
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.
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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.
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Vestibular ReflexesVestibular ReflexesVestibular ReflexesVestibular Reflexes
• Vestibulo-cervical:– Helps to maintain stability of the head
during movement of the torso.
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The vestibular labyrinthThe vestibular labyrinth The vestibular labyrinthThe vestibular labyrinth
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The Vestibular ApparatusThe Vestibular ApparatusThe Vestibular ApparatusThe Vestibular Apparatus
ComponentsComponentsa.a. Three semicircular canals (SCCs)Three semicircular canals (SCCs)
AnteriorAnterior PosteriorPosterior LateralLateral
b.b. Utricle and SacculeUtricle and Sacculec.c. Vestibular nerve and nucleiVestibular nerve and nuclei
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• there are five receptor organs housed in each of the two vestibular labyrinths:
1. hair cells in the utricle
2. hair cells in the saccule
3. hair cells in the anterior vertical semicircular canal
4. hair cells in the horizontal semicircular canal
5. 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 receptorsVestibular receptorsVestibular receptors
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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
Stimulus to the vestibular Stimulus to the vestibular sensory organssensory organs
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Vestibular receptorsVestibular receptorsVestibular receptorsVestibular receptors
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Static EquilibriumStatic EquilibriumStatic EquilibriumStatic Equilibrium
Inside the vestibule are two chambers :
utricle and saccule.
Regions of hair cells and supporting cells called maculae.
Otoliths – “ear rocks”
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The Utricle and SacculeThe Utricle and SacculeThe 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
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MaculaeMaculae MaculaeMaculae
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The Semicircular CanalsThe Semicircular CanalsThe 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 materiala. Ampulla
b. Cristae = hair cells
c. Cupulae = gelatinous material
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the vestibular labyrinththe vestibular labyrinth the vestibular labyrinththe vestibular labyrinth
Anterior
Lateral
Posterior
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Otolithic membrane
Hair cell
Anatomy: Maculae of Utricle or SacculePhysiology: Linear acceleration of head
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• 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 pathwaysVestibular pathwaysVestibular pathways
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Vestibulo-Ocular Reflex (VOR)Vestibulo-Ocular Reflex (VOR)Vestibulo-Ocular Reflex (VOR)Vestibulo-Ocular Reflex (VOR)
STIMULUS =Head movement
Efferent = oculomotor nervesEffector = Extra-ocular muscles
Sensory = Vestibular HC
Afferent = vestibular nerve
Center
Vestibulo-ocularHelps maintain stability of visual fieldLeads to physiologic nystagmus
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• 1st 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 1st order sensory neurons synapses with 2nd order sensory neurons (interneurons) in the vestibular nuclei
Vestibular pathwaysVestibular pathwaysVestibular pathwaysVestibular pathways
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Vestibular pathwaysVestibular pathwaysVestibular pathwaysVestibular pathways
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• 2nd order sensory neurons in vestibular nuclei
- integrate signals from vestibular organs with those fromo spinal cordo cerebellumo visual system
- project to 3rd order sensory neurons in o the ventral nuclei of the
thalamuso oculomotor nucleio reticular centers occupied with
skeletal movemento spinal centers occupied with
skeletal movemento vestibulocerebellum
Vestibular pathwaysVestibular pathwaysVestibular pathwaysVestibular pathways
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• 3rd 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 areasVestibular processing areasVestibular processing areas
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