these is 20 minutes presentation on vestibular system,presented by girmay fitiwi addis ababa university ,medical faculity departement of medical physiology.

1. Addis Ababa UniversityCollege of Health ScienceDepartment of Medical Physiology Presentation on physiology of vestibular apparatus and clinical correlates By Girmay F. 1 8/10/2011

2. Presentation Out line Objectives Introduction Anatomy of Vestibular apparatus 3.1 The otolithic organs 3.2 Semicircular canals 3.3 Structures of hair cell and genesis action potential 4.Function of the utricle and saccule 5. Function of semicircular ducts. 6. Neural connection of vestibular nuclei 7. vestibule-ocular reflex. 8. Vestibular dysfunction 9. References 8/10/2011 2

3. 1.Objectives At the end of presentation ,students expected to 1.Describe the anatomy and function of the vestibular apparatus 2.Explain the major input and out put of vestibular nuclei 3.Discuss the importance of vestibule ocular reflex. 4.List some clinical disorders of body equilibrium. 8/10/2011 3

4. 2.Introduction Gravity or acceleration tends to cause displacement of the body from equilibrium. Posture is back ground position which helps in carrying out a specific movement to desired target. Postural reflexes are integrated at various levels of the neural axis. The vestibular system has important sensory functions, contributing to the perception of self-motion, head position, and spatial orientation relative to gravity. It help to stabilize gaze head, and posture. 8/10/2011 4

6. semicircular canals

7. two otolith organs.8/10/2011 5 Fig.1.membranous labyrinth

9. Detect orientation of head with respect to gravity.

10. Macula is the sensory organ

11. Located on the inside surface of each utricle and saccule

12. Macula 2 mm in diameter.fig.2. location of macula

13. otolithic organs Cont’d Containing - sustentacular cells - numerous hair cells the Cilia embedded in gelatinous layer called statoconia. Impregnated with calcium carbonate crystals which are called otoconia or ear dust Base and side of hair cells vestibular nerve. 8/10/2011 7 Fig.5.structure of macula

18. Horizontal(lateral)

19. posterior

20. Right angles to each otherEach canal is a continuous endolymph-filled . Enlargement at one of its end called ampulla. 8/10/2011 10 Fig.6.parts of SCC.

21. Semicircular canals Cont’d Ampulla containing a receptor organ called crista ampullaris. The projecting cilia are embedded in gelatinous mass called cupula. The cupula extends right across the lumen up to the opposite wall of ampulla. 8/10/2011 11 Fig.7.structure of crista ampullaris

22. 3.3 Structure of hair cells and genesis of action potential Each hair cell has about 50-70 stereocilia and one kinocilium. Arising from its apical end. Stereocilia and the kinocilium are connected by tip links 8/10/2011 Fig.8 structure of hair cell 12

23. Structure of hair cells Cont’d 8/10/2011 13 Fig.9.A,B,C

24. structure of hair cells Cont’d When stereocilia bend towards kinocilium membrane receptor depolarization the impulse traffic increases When stereocilia bend away from kinocilium membrane receptor repolarization decreases the impulse traffic Orientation of the head in space changes and the weight of the statoconia bend the cilia, appropriate signals are transmitted to the brain to control equilibrium. 8/10/2011 14

25. 4.The function of utricle and saccule 1.Detection of Linear acceleration When the body suddenly thrust forward-(i.e. the body accelerates) The statoconia,fallbackward on the hair cell cilia, and information of dysequilibrium is sent into the nervous centers, causing the person to feel as though he or she were falling backward. This automatically causes the person to lean forward until the resulting anterior shift of the statoconia exactly equals the tendency for the statoconia to fall backward because of the acceleration. 8/10/2011 15

26. 5.The function of Utricle and Saccule cont’d 2.Maintenance of static equilibrium The hair cells are all oriented in different directions in the maculae of the utricles and saccules, so that with different positions of the head, different hair cells become stimulated. The “patterns” of stimulation of the different hair cells apprise the brain of the position of the head with respect to the pull of gravity. In turn, the vestibular, cerebellar, and reticular motor nerve systems of the brain excite appropriate postural muscles to maintain proper equilibrium. 8/10/2011 16

27. The function 0f Semicircular Ducts Detect angular acceleration Rotational acceleration stimulates crista ampullaris. The endolymph is displaced in a direction opposite to the direction of rotation. The fluid pushes on the cupula, deforming it. 8/10/2011 Fig.10.movement of SCC with body 17

28. The function of semicircular ducts cont’d this bends the processes of the hair cells. When a constant speed of rotation is reached the fluid rotate at the same rate as the body and the cupula swings back into the upright position . 8/10/2011 18

30. It returns to mid position in 25 to 30 seconds.8/10/2011 Fig.11.mov’t of endolymph with respect to SCCs 19

31. The function of semicircular canals Cont’d Simultaneously, the cilia at the top of the hair cell are bent. If the direction of bending is towards the kinocilium, depolarization takes place. Bending of the cilia in the reverse direction causes hyperpolarization; this alters impulse traffic along the nerves innervating the hair cells. 8/10/2011 20

33. Cerebellum, Brain stem

34. Spinal cord

35. cerebra cortical areas.8/10/2011 Fig.12.inputs of vestibular nuclei 21

37. Neural connection of vestibular nuclei cont’d Primary cortical center for equilibrium located in the parietal lobe. Flocculonodular lobe of cerebellum concerned with dynamic equilibrium. 8/10/2011 23 Fig.14 Inputs and out puts of vestibular nuclei

38. Neural connection of vestibular nuclei cont’d 8/10/2011 Fig.14. 24

39. Neural connection of vestibular nuclei cont’d 8/10/2011 Fig.15.descending projection of vestibular nuclei to spinal cord 25

40. Neural connection of vestibular nuclei cont’d Descending projections from the medial and lateral vestibular nuclei to the spinal cord. The MVN project bilaterally in the MLF to reach the medial part of the ventral horns and mediate head reflexes in response to activation of semicircular canals. The LVN sends axons via the LVT to contact anterior horn cells innervating the axial and proximal limb muscles. Neurons in the LVN receive input from the cerebellum, allowing the cerebellum to influence posture and equilibrium. 8/10/2011 26

41. 7.Vestibulo ocular reflex Stabilizes images on retina during head movement . When rotation starts, the eyes move slowly in a direction opposite to the direction of rotation, maintaining visual fixation. When the limit of this movement is reached, the eyes quickly snap back to a new fixation point and then again move slowly in the other direction. 8/10/2011 27 Fig.16. VOR

43. 8.Vestibular dysfunction Peripheral vestibular disorder Central vestibular disorder Loss of equilibrium and postural adjustments. PVD = neuritis, labyrinthitis,meniere’s disease, BPPV,and following surgery . 8/10/2011 29

44. 8.1Benign paroxysmal positional vertigo the most common vestibular disorder characterized by episodes of vertigo that occur with particular changes in body position. Possible cause is that otoconia from the utricle separate from the otolith membrane and become lodged in the cupula of the posterior semicircular canal. This causes abnormal deflections when the head changes position relative to gravity. 8/10/2011 30

46. multiple sclerosis, and cerebellar degeneration.8/10/2011 31

47. 8.3 Nystagmus jerky movement of the eye observed at the start and end of a period of rotation. Back and forth or rotational eye movements. The movements will be slower in one direction. The direction of eye movement is identified by the direction of the quick component. 8/10/2011 32

48. 8.4 Motion sickness Excessive vestibular stimulation The symptoms are probably due to reflexes mediated via vestibular connections in the brain stem and the flocculonodular lobe of the cerebellum. symptom Nausea, blood pressure changes, sweating, pallor 8/10/2011 33

49. 9.References Berne and levy physiology 6thedition,bruce m koeppen and Bruce A. Stanton. Guyton and hall text book of medical physiology,12th edition, Philadelphia: Elsevier Inc. Ganong’s review of medical physiology 23th edition. Mc Graw Hill Neuroscience exploring the brain Third Edition.Dale Purves George J. Augustine, Sinauer Associates, Inc. Publishers Sunderland, Massachusetts U.S.A. Internet websites 8/10/2011 34

50. Thank you !!! 8/10/2011 35