Vestibular System. Dian Yu, class of 2016

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1 Vestibular System Dian Yu, class of 2016

2 Objectives 1. Describe the functions of the vestibular system: What is it? How do you stimulate it? What are the consequences of stimulation? 2. Describe the vestibular apparatus, the 2 vestibular organs, and their unique sensory receptors 3. Describe the 1st and 2nd order neurons in vestibular pathways 4. Describe the pathways mediating vestibular perception and reflexes 5. Descibe the vestibular tests used for clinical assessment 6. Discuss the symptoms and basis of disorders including acoustic neuroma and benign paroxysmal positional vertigo Chris Cohan, Ph.D. Dept. of Pathology/Anat Sci Jacobs School of Medicine

3 A 70 year-old woman complains of several episodes of dizziness for the past month. Symptoms: when she awakens in morning and rolls over, she feels like room is spinning lasts about 20 sec, but sometimes nausea/vomiting brief periods of dizziness when she stands or shakes her head. Has caused her to fall. No change in hearing or ringing in ears

4 VESTIBULAR SYSTEM What is vestibular sensation Where are vestibular sensory organs How is vestibular info used by the CNS What are clinical implications of vestibular stimulation and vestibular lesions.

5 Vestibular Stimulation Induced by head motion or change in head position FUNCTIONS 1. Perception of head movement/head position. Reflexive control of: 2. Posture and balance - ability to stand upright 3. Head position - head upright on shoulders 4. Eye-head coordination - vestibulo-ocular reflex 5. Autonomic Centers Deficits vertigo falling tilting nystagmus nausea

6 All sensory systems have pathways for perception and reflexes. In the vestibular system, REFLEXES dominate You are not usually aware of vestibular sensation unless there is a problem.

7 Inner Ear

8 Vestibular Apparatus Bony and Membranous Labyrinth Perilymphatic Space

9 Vestibular Apparatus 2 Vestibular Organs: Semicircular Canals Utricle and Saccule

10 In semicircular canals, sensory epithelium is the crista ampullares Vestibular Receptors ampulla cupula duct crista ampulla cupula

11 Vestibular Receptors The utricle/saccule are expanded areas that contain sensory epithelium called the Macula. The macula is similar to the crista except that the gelatinous membrane covering its hair cells is flat and contains particles that increase its weight so that it can respond to gravity. Otolithic Membrane Macula

12 Apical surface - Stereocilia Hair Cells Stereocilia decrease in length from the kinocilium. This provides an important physiological feature that allows bending to modulate transmitter release onto dendrites of 1st order neurons (CN VIII).

13 Vestibular Structures First-order neurons in vestibular ganglion Bipolar neurons axon dendrite

14 Vestibular Structures CN VIII enters brainstem at cerebello-pontine angle location of: cerebellum, pons, medulla, CN VII, CN VIII

15 Vestibular Structures Second-order neurons: the 4 vestibular nuclei S L M I in caudal pons/rostral medulla S L M I To cerebellum cerebellum axons travel in inferior cerebellar peduncle nodulus flocculus Both the vestibular nuclei and cerebellum are REQUIRED for vestibular function

16 Lesions of Vestibular Structures Damage to the vestibular nuclei lateral area of caudal pons and rostral medulla or flocculus/nodulus of cerebellum causes generalized vestibular symptoms!! - falling, wide-based gait, nystagmus, nausea, vertigo

17 1. Perception 2. Posture and balance 3. Head position 4. Eye-head coordination 5. Autonomic Centers Vestibular Pathways Vestibular Nuclei VPL Parieto-temporal cortex Vestibular disruption/lesions cause vertigo (feeling of movement).

18 1. Perception 2. Posture and balance 3. Head position 4. Eye-head coordination 5. Autonomic Centers Maintaining Balance i. Vestibular system - required vertigo has over-riding effect eg after spinning it is difficult to maintain upright posture using vision or proprioception ii. Visual system - provides external reference iii. Proprioception - info about the body rather than head. Romberg Test

19 1. Perception 2. Posture and balance 3. Head position 4. Eye-head coordination 5. Autonomic Centers Vestibular Pathways 2. Posture/Balance strong excitation to extensor muscles - counter gravity and maintain posture/balance. Ipsilateral tract supports posture on same side. LVST Lesions cause falling to same side. Lateral vestibulospinal tract

Head Position Visual perception is aided by upright head position Vestibular stimuli during a

20 1. Perception 2. Posture and balance 3. Head position 4. Eye-head coordination 5. Autonomic Centers Vestibular Pathways 3. Head Position Visual perception is aided by upright head position Vestibular stimuli during a fall forward, activate neck extensors to protect the head. Lesions cause altered head posture/head oscillation. MVST Medial vestibulospinal tract controls neck muscles

21 1. Perception 2. Posture and balance 3. Head position 4. Eye-head coordination 5. Autonomic Centers Vestibular Pathways 4. Eye-Head Movements MLF vestibulo-ocular reflex Head rotation induces compensatory movement of the eyes in the opposite direction to maintain visual fixation. III VI Lesions cause nystagmus. vest nuc

22 1. Perception 2. Posture and balance 3. Head position 4. Eye-head coordination 5. Autonomic Centers Vestibular Pathways 5. Autonomic Centers in rostral medulla Chemoreceptive trigger zone Vomiting center in Lateral RF Lesions cause nausea/vomiting.

23 Effects of Vestibular Stimulation Vertigo perceived motion in absence of movement Loss of Balance/Falling Nystagmus (spontaneous or induced forms) Nausea/Vomiting MLF LVST MVST Nystagmus may be ongoing or evoked by an eye movement.

24 Stimulating/Testing the Vestibular System Tests irritability and intact pathway 1. Head rotation - Oculocephalic Reflex (Doll s Eye Maneuver) conjugate eye movements 2. Caloric Test cold or warm water infused into external auditory meatus conjugate eye movements (see 3. Rotation in Barañy Chair (conscious) see Dr Baizer s handout

25 Doll s Eyes Maneuver In a comatose patient, moving the head from side to side or up and down causes the eyes to move in the direction opposite to head movement due to stimulation of the semicircular canals. These movements are known as Doll s Eyes. This result indicates intact brainstem pathways. With brainstem damage, the eyes move in the direction of head movement (absent oculocephalic reflex). In a conscious patient, when the same maneuver is done, the direction of eye movement depends upon whether the subject s eyes are fixated on an object. Typically, fixation is not the case and the eyes move with the head.

26 Clinical Importance of Brainstem Reflexes CASE: On returning home from shopping, a wife finds her 59 year-old husband unconscious on the floor. He has no pulse. After calling 911, she begins CPR. When Mr. T arrives in the ED, he is in ventricular fibrillation. Spontaneous circulation is eventually restored, but Mr. T remains comatose. After 3 days in coma, his wife asks about her husband s condition and the probability of a good outcome. How assess extent of CNS damage/function in unconscious patient 1. Somatosensory Evoked Potential 2. Corneal reflex 3. Pupillary Constriction Reflex 4. Oculocephalic Reflex or Caloric Test

27 Vestibular System Lesions Recognize vestibular symptoms Source may be peripheral or CNS When CNS, typically multiple symptoms indicate lesion in vestibular nuclei or vestibular areas of cerebellum More localized lesions (eg MLF) produce more specific symptoms. to cortex MLF LVST MVST

28 A benign, slow-growing tumor of schwann cells in CN VIII. It may involve CN V and CN VII also. Acoustic Neuroma

29 Case Solution A 70 year-old woman complains of several episodes of dizziness for the past month. Symptoms: when she awakens in morning and rolls over, she feels like room is spinning lasts about 20 sec, but sometimes nausea/vomiting brief periods of dizziness when she stands or shakes her head. Has caused her to fall. No change in hearing or ringing in ears

30 Case Solution 1. What does she mean by dizziness? vertigo 2. Relatedness of spinning room, nausea, falling, no hearing and ringing in ears? 3. What causes this condition? Benign Paroxysmal Positional Vertigo Symptoms of vestibular over-stimulation

idiopathic/aging, head trauma, infection Pathophys: Dislodged otoconia move

31 Benign Paroxysmal Positional Vertigo non-progressing condition with brief periods of severe vertigo sudden change in head position Risk Fac: idiopathic/aging, head trauma, infection Pathophys: Dislodged otoconia move into semicircular canals to stimulate crista abnormally Treatment: Otolith Repositioning Procedure

32 Otolith Repositioning Procedure

VESTIBULAR SYSTEM. Deficits cause: Vertigo. Falling Tilting Nystagmus Nausea, vomiting

VESTIBULAR SYSTEM. Deficits cause: Vertigo. Falling Tilting Nystagmus Nausea, vomiting VESTIBULAR SYSTEM Objectives: Understand the functions of the vestibular system: What is it? How do you stimulate it? What are the consequences of stimulation? Describe the vestibular apparatus, the 2