Physiology of equilibrium & balance


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Physiology of equilibrium & balance

  1. 1. Physiology of Body Equilibrium & Balance SYED TOUSIF AHMED
  2. 2. Centre of gravity To balance the centre of gravity must be above the support point.
  3. 3. Physiology Of Body Balance
  4. 4. Physiology Of Body Balance
  5. 5. Balance : <ul><li>Balance : ability to control equilibrium </li></ul><ul><li>Foot position affects standing balance </li></ul><ul><ul><li>Is defined as : </li></ul></ul><ul><ul><li>“ THE ABILITY TO MAINTAIN THE EQUILIBRIUM OF THE BODY.” </li></ul></ul>
  6. 6. Equilibrium <ul><li>Is defined as : </li></ul><ul><li>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. </li></ul><ul><li>There are 2 types of balance </li></ul><ul><ul><ul><ul><ul><li>Static - </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Dynamic – </li></ul></ul></ul></ul></ul>
  7. 7. BALANCE Anticipatory Mechanisms (internal) Proactive Mechanisms (external) Reactive Mechanisms Sensory Systems Body Schema Neuro-muscular Synergies Musculo-skeletal Components
  8. 8. Balance and Orientation Pathways
  9. 9. CNS 1- Cerebral cortex 2- Brainstem 3- Cerebellum 2- Vestibular 3- Proprioceptive 1- visual Muscle commands 1- 2- Systems regulating body balance <ul><li>Humans use three systems: </li></ul>
  10. 10. The Cerebellum <ul><li>11% of brain mass </li></ul><ul><li>Dorsal to the pons and medulla </li></ul><ul><li>Controls f ine movement coordination </li></ul><ul><li>Balance and equilibrium </li></ul><ul><li>Muscle tone </li></ul>
  11. 11. Anatomy of the Cerebellum <ul><li>Two hemispheres connected by vermis </li></ul><ul><li>Each hemisphere has three lobes </li></ul><ul><ul><li>Anterior, posterior, and flocculonodular </li></ul></ul><ul><li>Folia—transversely oriented gyri </li></ul><ul><li>Arbor vitae—distinctive treelike pattern of the cerebellar white matter </li></ul>
  12. 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. 13. Cerebellum Cortico cerebellum Vestibulo cerebellum Spinocerebellum
  14. 14. Vestibulocerebellum <ul><li>controls tone & movements of muscles involved in equilibrium & posture, by receiving impulses from vestibular apparatus. </li></ul>
  15. 15. Spinocerebellum <ul><li>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 . </li></ul>
  16. 16. Corticocerebellum <ul><li>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) </li></ul>
  17. 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).
  18. 19. Cerebellar Cortical Circuits
  19. 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.
  20. 22. Static Equilibrium 1) keep the body in a desired position , Static equilibrium – The equilibrium is maintained in a FIXED POSITION , usually while stood on one foot. maintenance of body posture relative to gravity while the body is still.
  21. 23. Dynamic Equilibrium 2) move the body in a controlled way . Dynamic equilibrium The equilibrium must be maintained while performing a task which involves MOVEMENT e.g. Walking the beam. – maintenance of the body posture (mainly the head) in response to sudden movements. Tracking a moving object.
  22. 24. Vestibular Reflexes <ul><li>Vestibulo-cervical: </li></ul><ul><ul><li>Helps to maintain stability of the head during movement of the torso. </li></ul></ul>
  23. 25. The vestibular labyrinth
  24. 26. The Vestibular Apparatus <ul><li>Components </li></ul><ul><li>Three semicircular canals (SCCs) </li></ul><ul><ul><li>Anterior </li></ul></ul><ul><ul><li>Posterior </li></ul></ul><ul><ul><li>Lateral </li></ul></ul><ul><li>Utricle and Saccule </li></ul><ul><li>Vestibular nerve and nuclei </li></ul>
  25. 27. <ul><li>there are five receptor organs housed in each of the two vestibular labyrinths: </li></ul><ul><li>hair cells in the utricle </li></ul><ul><li>hair cells in the saccule </li></ul><ul><li>hair cells in the anterior vertical semicircular canal </li></ul><ul><li>hair cells in the horizontal semicircular canal </li></ul><ul><li>hair cells in the posterior vertical semicircular canal </li></ul><ul><li> the displacement of hair cells – due to the forces of gravity and inertia – transduce mechanical stimuli into receptor potentials </li></ul>Detect linear accelerations along any axis Detect angular accelerations about any axis Vestibular receptors
  26. 28. <ul><li>Mechanism of Stimulation </li></ul><ul><li>Deflection of stereocilia towards kinocilium =Stimulation </li></ul><ul><li>Deflection of stereocilia away from kinocilium = Inhibition </li></ul>Stimulus to the vestibular sensory organs
  27. 29. Vestibular receptors
  28. 30. Static Equilibrium Inside the vestibule are two chambers : utricle and saccule . Regions of hair cells and supporting cells called maculae . Otoliths – “ear rocks”
  29. 31. The Utricle and Saccule <ul><li>Present in the vestibule of the labyrinth </li></ul><ul><li>Utricle is vertically oriented </li></ul><ul><li>Saccule is horizontally oriented </li></ul><ul><li>Sensory hair cells are embedded in the maculae of the utricle and saccule </li></ul><ul><li>Hair cells are covered by a membrane called otolithic membrane </li></ul>
  30. 32. Maculae
  31. 33. The Semicircular Canals <ul><ul><ul><li>Fluid filled </li></ul></ul></ul><ul><ul><ul><li>Each canal has a dilated end = Ampulla </li></ul></ul></ul><ul><ul><ul><li>The ampulla houses the sensory hair cells which are covered by a gelatinous material </li></ul></ul></ul><ul><ul><ul><ul><li>Ampulla </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Cristae = hair cells </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Cupulae = gelatinous material </li></ul></ul></ul></ul>
  32. 34. the vestibular labyrinth Anterior Lateral Posterior
  33. 35. Otolithic membrane Hair cell Anatomy: Maculae of Utricle or Saccule Physiology: Linear acceleration of head
  34. 36. <ul><li>the vestibulo-ocular reflex is an example of a reflexive eye movement that exists between semicircular canals and nuclei controlling extrinsic eye muscles </li></ul>Vestibular pathways
  35. 38. Vestibulo-Ocular Reflex (VOR) STIMULUS = Head movement Efferent = oculomotor nerves Effector = Extra-ocular muscles Sensory = Vestibular HC Afferent = vestibular nerve Center <ul><li>Vestibulo-ocular </li></ul><ul><ul><li>Helps maintain stability of visual field </li></ul></ul><ul><ul><li>Leads to physiologic nystagmus </li></ul></ul>
  36. 39. <ul><li>1 st order sensory neurons : </li></ul><ul><li>dendrites surround base of hair cells in vestibule and semicircular canals </li></ul><ul><li>cell bodies located in the vestibular ganglion </li></ul><ul><li>the vestibular ganglion lies in a swelling of the vestibular nerve within the internal auditory meatus </li></ul><ul><li>about 20,000 axons join to form vestibular nerve , which joins cochlear nerve to form vestibulocochlear nerve </li></ul><ul><li>vestibular nerve portion projects to the ipsilateral complex of four major vestibular nuclei in the dorsal part of the pons and medulla </li></ul><ul><li>axons of 1 st order sensory neurons synapses with 2 nd order sensory neurons (interneurons) in the vestibular nuclei </li></ul>Vestibular pathways
  37. 40. Vestibular pathways
  38. 41. <ul><li>2 nd order sensory neurons in vestibular nuclei </li></ul><ul><li>- integrate signals from vestibular organs with those from </li></ul><ul><ul><li>spinal cord </li></ul></ul><ul><ul><li>cerebellum </li></ul></ul><ul><ul><li>visual system </li></ul></ul><ul><li>project to 3 rd order sensory neurons in </li></ul><ul><ul><li>the ventral nuclei of the thalamus </li></ul></ul><ul><ul><li>oculomotor nuclei </li></ul></ul><ul><ul><li>reticular centers occupied with skeletal movement </li></ul></ul><ul><ul><li>spinal centers occupied with skeletal movement </li></ul></ul><ul><ul><li>vestibulocerebellum </li></ul></ul>Vestibular pathways
  39. 42. <ul><li>3 rd order sensory neurons </li></ul><ul><li>in the ventral thalamus send axons to synapse with neurons in vestibular area (Brodmann’s area 2V and 3a) of the primary somatosensory cortex </li></ul><ul><li>- 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 </li></ul>Vestibular processing areas
  40. 43. THE END