Cns 15


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Cns 15

  1. 1. Systems regulating body balance <ul><li>Senses from the environment </li></ul><ul><li>Summation and coordination of senses in the CNS </li></ul><ul><li>Motor commands to muscle regulation of body balance </li></ul>There are three components that regulate body balance
  2. 2. CNS 1- Cerebral cortex 2- Brainstem 3- Cerebellum 2- Vestibular 3- Proprioceptive 1- Muscle commands 1- 2- Systems regulating body balance
  3. 3. 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><ul><li>These organs contain the sensory hair receptors: </li></ul><ul><ul><li>the maculae (for the utricle & saccule) </li></ul></ul><ul><ul><li>and cristae (ampullae). </li></ul></ul>
  4. 4. Anatomy of the vestibular labyrinth Anterior Lateral Posterior
  5. 5. The Semicircular Canals <ul><li>Fluid filled </li></ul><ul><li>Each canal has a dilated end = Ampulla </li></ul><ul><li>The ampulla houses the sensory hair cells which are covered by a gelatinous material </li></ul><ul><ul><li>Ampulla </li></ul></ul><ul><ul><li>Cristae = hair cells </li></ul></ul><ul><ul><li>Cupulae = gelatinous material </li></ul></ul>
  6. 8. Cupula Cristae Ampulla
  7. 9. Sensory cell (Hair cell) Kinocilium Stereocilia Stimulation Inhibition Afferent vestibular nerve fibers
  8. 10. 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>
  9. 11. The vestibule of the labyrinth
  10. 12. Otolithic membrane Hair cell Anatomy: Maculae of Utricle or Saccule Physiology: Linear acceleration of head
  11. 13. Types of Equilibrium <ul><li>Static equilibrium : is concerned with the orientation of the body relative to the ground ( Linear acceleration) </li></ul><ul><li>Dynamic equilibrium is concerned with the maintenance of posture, especially in the head ( Rotational movement) </li></ul>Rotational movement
  12. 14. Stimulus to the vestibular sensory organs <ul><li>= </li></ul><ul><li>Motion </li></ul><ul><li>Velocity </li></ul><ul><li>Acceleration </li></ul><ul><li>Head acceleration in an angular fashion stimulates SCCs </li></ul><ul><li>Head acceleration in a linear fashion stimulates maculae in utricle and saccule </li></ul>
  13. 15. <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
  14. 16. Dynamic Equilibrium <ul><li>The receptors for Dynamic equilibrium are the ampulla which is found in the semicircular canals. </li></ul><ul><li>In each ampulla is a small elevation called a crista. Each crista is made up of hair (receptor) cells and supporting cells, and covered by a jelly-like material known as the cupola. Movement of the cupola stimulates the hair cells </li></ul>Ampulla
  15. 17. Dynamic Equilibrium <ul><li>The ampulla is responsible for the change in rotational movement , as continuous rotation does not stimulate the ampulla. </li></ul><ul><ul><li>when the head starts moving in a rotationally the endolymph in the semicircular ducts move in the direction opposite to the body ’ s direction deforming the crista in the duct causes depolarization </li></ul></ul><ul><ul><li>If the body continues to rotate at a constant rate The endolymph moves at the same direction and speed as the body and stop the movement of hair cells </li></ul></ul>
  16. 18. Dynamic Equilibrium <ul><li>When we suddenly stop moving, the endolymph keeps on moving in the opposite direction hyperpolarization of the hair cells that will tell the brain that we have stopped movement. </li></ul>
  17. 19. Otolithic membrane Hair cell Mechanism of Stimulation in Utricle & Saccule 1- Linear acceleration of head or changes of head position 2- Shift of position of otolithic membrane 3- Deflect stereocilia to or away from kinocilium 4- Stimulation or inhibition
  18. 20. Linear Acceleration Stimuli <ul><li>When the head starts or stops moving in a linear </li></ul><ul><li>acceleration otolothic membrane slides backward or forward over hair cells the hair cells will bend </li></ul>
  19. 21. <ul><li>When the hair bends towards the kinocilium the hair cell depolarize faster steam of impulse is sent to the brain </li></ul>Linear Acceleration Stimuli Nerve Action Potential <ul><li>When the hair bends in the opposite direction the hair cells hyperpolarize Slower impulse generation </li></ul>NOTE : It is important to understand that the maculae is responsible for the change in acceleration only. Because the hair cell can adapt it quickly
  20. 22. Static Equilibrium <ul><li>The Maculae are responsible for linear acceleration forces. </li></ul><ul><li>The Maculae are in the </li></ul><ul><ul><li>Saccule : is responsible for </li></ul></ul><ul><ul><li>vertical acceleration </li></ul></ul><ul><ul><li>Utricle: Is responsible for </li></ul></ul><ul><ul><li>horizontal acceleration </li></ul></ul>Maculae in Saccule & utricle Saccule Utricle
  21. 23. Connections of the vestibular sensory organs <ul><li>Vestibulo-Ocular reflex (VOR) </li></ul><ul><li>Vestibulo-Spinal reflex (VSR) </li></ul>
  22. 24. Function of vestibular reflexes <ul><li>The VOR stabilizes gaze during fast head movement </li></ul><ul><li>The VSR sends information regarding gravity and linear acceleration to body muscles </li></ul>
  23. 25. Vestibulo-Ocular Reflex (VOR) STIMULUS = Head movement Efferent = oculomotor nerves Effector = Extra-ocular muscles Sensory = Vestibular HC Afferent = vestibular nerve Center
  24. 26. Vestibulo-Spinal Reflex (VSR) STIMULUS = Gravity linear acceleration Efferent = Spinal nerves Effector = Neck and body muscles Sensory = Vestibular HC Afferent = vestibular nerve Center
  25. 27. The Visual System <ul><li>The 2 nd system that plays an important role in equilibrium is the visual system. </li></ul><ul><li>The effect of the visual system is best noticed when there is a conflict between the messages that reach the brain. </li></ul><ul><li>Motion sickness is a very common equilibrium disorder in which is due to sensory input mismatch. The main symptoms are: Nausea, dizziness, vomiting and pale appearance </li></ul>
  26. 28. Motion sickness <ul><li>When a person reads while traveling, the visual inputs indicates that the body is fixed. But as the vehicle is moving the vestibular system detects movement and send impulses that conflict with the visual system. </li></ul><ul><ul><li>The Brain receives conflicting information which will lead to motion sickness. </li></ul></ul>
  27. 29. Vestibular Evaluation <ul><li>Taking History </li></ul><ul><li>- Complaints </li></ul><ul><li>- History of present illness </li></ul><ul><li>- Past medical history </li></ul><ul><li>Question the character of “Dizziness” </li></ul><ul><li>(spinning, blurring of vision, loss of balance, light headedness,….) </li></ul><ul><li>Character of course of dizziness </li></ul><ul><li>(onset, duration: sec/min/hrs/days, in attacks or constant, position, alleviation, aggravation,…) </li></ul>
  28. 30. Vestibular evaluation <ul><li>Associated symptoms </li></ul><ul><ul><li>otologic (tinnitus, fullness, otalgia, draining ear,…) </li></ul></ul><ul><ul><li>Neurologic (headache, migraine, epilepsy, diplopia, tremors, …) </li></ul></ul><ul><ul><li>Psychiatric (anxiety, pallor, sweating, depression,…) </li></ul></ul><ul><ul><li>Cardiac (syncope, arrhythmias) </li></ul></ul><ul><ul><li>Medication side effects (ototoxic drugs) </li></ul></ul>
  29. 31. Physical examination <ul><li>Standard ENT examination </li></ul><ul><li>Examine VOR for presence of nystagmus </li></ul><ul><li>Examine VSR by testing: </li></ul><ul><li>- Balance and gait </li></ul><ul><li>- Posture </li></ul><ul><li>- Coordination </li></ul><ul><li>- Fine motor skills </li></ul>
  30. 32. Nystagmus <ul><li>Nystagmus = rhythmic involuntary oscillation of eyes with fast and slow phases </li></ul>
  31. 33. Examination of nystagmus <ul><li>Observe for eye movements in darkness or with Frenzel’s glasses </li></ul><ul><li>Observe for eye movements with eyes open for fixation suppression </li></ul>
  32. 34. Vestibular nystagmus <ul><li>Spontaneous </li></ul><ul><li>Induced </li></ul><ul><li>Peripheral or Central </li></ul>
  33. 35. Spontaneous nystagmus <ul><li>Peripheral lesion </li></ul><ul><li>Examples: </li></ul><ul><li>1- Acute labyrinthitis </li></ul><ul><li>2- Vestibular neuronitis </li></ul><ul><li>3- Meniere’s disease </li></ul><ul><li>Usually unilateral </li></ul><ul><li>Suppressed by visual fixation </li></ul><ul><li>Associated otologic symptoms </li></ul>
  34. 36. Spontaneous nystagmus <ul><li>Central lesion </li></ul><ul><li>Not suppressed by </li></ul><ul><li>visual fixation </li></ul><ul><li>Associated neurologic symptoms </li></ul>
  35. 37. Induced nystagmus <ul><li>Nystagmus induced by position change </li></ul><ul><li>Nystagmus induced by caloric stimulation </li></ul>
  36. 38. Positional nystagmus <ul><li>Normally not present </li></ul><ul><li>Induced by position </li></ul><ul><li>Evaluation: </li></ul><ul><li>Hallpike maneuver </li></ul><ul><li>Peripheral or central </li></ul><ul><li>Characteristics: latent period, fatigable, +/- paroxysmal </li></ul>
  37. 39. Barany’s Caloric testing Concept <ul><li>Convection currents created in the endolymph will move the cupula inwards or outwards </li></ul><ul><li>Convection currents are created in the endolymph by irrigating the external auditory canal by warm water and cold water to be below or above body temperature. </li></ul>
  38. 40. Caloric testing Procedure and recording
  39. 41. Postural Reflexes <ul><li>Impossible to separate postural adjustments from voluntary movement </li></ul><ul><li>maintain body in up-right balanced position </li></ul><ul><li>provide constant adjustments necessary to maintain stable postural background for voluntary movement </li></ul><ul><li>adjustments include static reflexes (sustained contraction) & dynamic short term phasic reflexes (transient movements) </li></ul>
  40. 42. Postural Control (cont) <ul><li>A major factor is variation of in threshold of spinal stretch reflexes </li></ul><ul><li>caused by changes in excitability of motor neurons & changes in rate of discharge in the gamma efferent neurons to muscle spindles </li></ul>
  41. 43. Posture <ul><li>Represents overall position of the body & limbs relative to one another & their orientation in space </li></ul><ul><li>Postural adjustments are necessary for all motor tasks & need to be integrated with voluntary movement </li></ul>
  42. 44. Postural Adjustments <ul><li>Functions </li></ul><ul><ul><li>support head & body against gravity </li></ul></ul><ul><ul><li>maintain center of the body’s mass aligned & balanced over base of support on the ground </li></ul></ul><ul><ul><li>stabilize supporting parts of the body while others are being moved </li></ul></ul><ul><li>Major mechanisms </li></ul><ul><ul><li>anticipatory (feed forward)-predict disturbances </li></ul></ul><ul><ul><ul><li>modified by experience; improves with practice </li></ul></ul></ul><ul><ul><li>compensatory (feedback) </li></ul></ul><ul><ul><ul><li>evoked by sensory events following loss of balance </li></ul></ul></ul>
  43. 47. Righting reflexes Tonic neck reflexes Vestibular placing reaction