2. Anatomy and Physiology of Balance

7. Vestibular Hair Cells Type I (aka inner) Type II (aka outer) With Kinocilium

9. The Semicircular Canals posterior canal shares plane with contralateral anterior canal. horizontal canals share plane.

10. Stimulated by Angular Acceleration greatest when fulcrum is within head induces relative motion of endolymph crista is displaced by fluid motion

12. Responses of the Cristae All kinocilia are oriented in the same direction Crista in each pair of canals respond inversely to each other

13. The Otolithic Organs Saccule: roughly vertical orientation, responds to acceleration components within saggital plane Utricle: horizontal (+ 30 deg.) orientation

14. Excitation Patterns in the Utricle STRIOLA Posterior Anterior Medial

15. Cranial Nerve VIII

16. Vestibular Portion of C.N. VIII  superior division: utricle, anterior part of saccule, and horiz & anterior canals  inferior division: posterior part of saccule, and posterior canal to vestibular nuclei to cerebellum

17. Vestibulocochlear Nerve Exits temporal bone near its medial edge. Enters lateral face of brainstem at the level of the lower pons. Synapsing in (Cochlear and) Vestibular Nuclei

18. Responses of Vestibular Neurons: To changes in acceleration, but onset and fade slowly For most normal head movements firing rates are in phase with head VELOCITY.

20. Other inputs to vestibular nuclei: Cerebellum: primarily inhibitory Spinal cord Pontine reticular formation Contralateral vestibular nuclei

21. From the Vestibular Nuclei: Vestibulo-Oculomotor Pathways: –Direct: to oculomotor nuclei. –Indirect: via reticular formation to oculomotor nuclei (III IV and VI) Vestibulo-Spinal Pathways: –Lateral V-S-throughout spinal cord –Medial V-S-cervical & thoracic –Reticulospinal tract-via brainstem reticular formation

22. Median Longitudinal Fasciculus A tract linking Vest. Nuclei to nuclei of CN III, IV, & VI; Supports conjugate eye movement during movement of the head. Continuous with the medial vestibulospinal tract. The mlf runs near midline ventral to ventricle IV and the periaqueductal gray matter of the midbrain

25. In the brainstem Vestibular inputs undergo integration Integrated signal is combined with original (velocity driven) signal Processing to reset spatial map for eye musculature

26. Integration & “Leaky” Integration

28. The VOR

32. Central Nervous System Will Adapt to Peripheral Damage

33. Eye Movements Saccades—rapid shift in gaze Pursuit—stabilize image of moving object Fixation—stabilize image of still object VOR—stabilize image during head motion OKN—backup for when VOR decays to cont’d head rotation Vergent movements—change depth of focus

34. Pause cells inhibit Burst Neurons which stimulate: III & VI (horizontal) or III & IV (vertical) Saccades

39. Visual System Vestibular System Somato- Sensation Compare, Select & Combine Senses SENSORY INPUTS Vision Vestibular Somatosensory

40. Somato- Sensation Compare, Select & Combine Senses SOMATOSENSORY RECEPTORS Joints Position Kinesthesia Muscles Length Tension Skin Touch Pressure

41. Visual System Compare, Select & Combine Senses Central Orientation Navigation Peripheral Motion-sensitive Body-sway VISUALRECEPTORS

42. Vestibular System Compare, Select & Combine Senses Semi-circular canals Orientation Navigation Utricle & Saccule Horizontal & vertical acceleration & deceleration VESTIBULAR RECEPTORS

43. Selection based on Availability Accuracy Value for the task at hand Processing of inputs from the periphery SENSORY ORGANIZATION Compare, Select & Combine Senses Determination of Body Position VisualVestibularSomatosensory

44. Functional Balance: Navigating in our Environment

45. A Quiz Vestibular Pathways Quiz