Physiology of BodyPhysiology of Body EquilibriumEquilibrium & & Balance

SYED TOUSIF AHMED

Centre of gravity

To balance the centre of gravitymust be above the support point.

Physiology Of Body Physiology Of Body Balance

Physiology Of BodyPhysiology Of Body Balance

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.”

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 –

BALANCE

Anticipatory Mechanisms

(internal)

Proactive Mechanisms

(external)

ReactiveMechanisms

Sensory Systems

Body Schema

Neuro-muscular Synergies

Musculo-skeletal

Components

Balance and Orientation Pathways

CNSCNS1- Cerebral cortex2- Brainstem 3- Cerebellum

2 -Vestibular

3 -Proprioceptive

1 -visualvisualMuscle commands

1-

2-

Systems regulating body balance

•Humans use three systems:

The Cerebellum

• 11% of brain mass

• Dorsal to the pons and medulla

• Controls fine movement coordination

• Balance and equilibrium

• Muscle tone

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

Figure 12.17b

(b)

Medullaoblongata

Flocculonodularlobe

Choroidplexus offourth ventricle

Posteriorlobe

Arborvitae

Cerebellar cortex

Anterior lobe

Cerebellarpeduncles• Superior• Middle• Inferior

Cerebellum

Cortico cerebellum

Vestibulo cerebellum

Spinocerebellum

Vestibulocerebellum

• controls tone & movements of muscles involved

in equilibrium & posture, by receiving impulses

from vestibular apparatus.

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.

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)

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).

Cerebellar Cortical Circuits

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.

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.

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.

Vestibular ReflexesVestibular ReflexesVestibular ReflexesVestibular Reflexes

• Vestibulo-cervical:– Helps to maintain stability of the head

during movement of the torso.

The vestibular labyrinthThe vestibular labyrinth The vestibular labyrinthThe vestibular labyrinth

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

• 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

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

Vestibular receptorsVestibular receptorsVestibular receptorsVestibular receptors

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”

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

MaculaeMaculae MaculaeMaculae

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

the vestibular labyrinththe vestibular labyrinth the vestibular labyrinththe vestibular labyrinth

Anterior

Lateral

Posterior

Otolithic membrane

Hair cell

Anatomy: Maculae of Utricle or SacculePhysiology: Linear acceleration of head

• 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

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

• 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

Vestibular pathwaysVestibular pathwaysVestibular pathwaysVestibular pathways

• 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

• 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

THE END