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By Sanjay George
PHYSIOLOGY OF EQUILIBRIUM
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STRUCTURES INVOLVED IN MAINTENANCE OF BALANCE IN THE EAR
• Utricle and Saccule
• Semicircular Canals
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PHYSIOLOGY OF VESTIBULAR SYSTEM
• Peripheral – membranous labyrinth and vestibular nerve
• Central – made up of nuclei and fiber tracts in CNS
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UTRICLE
• Stimulated by linear acceleration and deceleration or gravitational pull during head tilts.
• Macula of utricle lies in horizontal plane on the inferior surface of utricle.
• Hair cells stimulated by displacement of otolithic membrane.
• Hair cells oriented in different directions.
• Determines orientation of the head when the head is upright.
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SACCULE
• Function similar to utricle.
• Macula of saccule located in a vertical plane and signals head orientation when person is lying down.
• Also responds to sound vibrations.
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SEMICIRCULAR CANALS• Responds to angular acceleration and deceleration.
• 3 canals lie at right angles to each other.
• Canal which lies at right angle to axis of rotation stimulated most.
• Stimulus – flow of endolymph displacing the cupula.
• Stimulation of semicircular canals produce nystagmus.
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MAINTENANCE OF EQUILIBRIUM
• Function of Utricle and Saccule :
• Hair cells in maculae oriented in different directions.
• With different position of head, stimulation of different hair cells apprise the brain of the position of the head.
• In turn Vestibular, cerebellar and reticular motor systems excite appropriate postural muscles.
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• Detection of linear acceleration and deceleration by the utricle and saccule:
• Otoliths fall back on hair cells during acceleration and deceleration.
• Information of disequilibrium causes person to shift.
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• Detection of head rotation by semicircular ducts
• Predictive function of semi circular canals:
• Predicts disequilibrium is going to occur and thereby causes equilibrium centers to make appropriate anticipatory preventive adjustments.
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OTHER FACTORS CONCERNED WITH EQUILIBRIUM
• Visual Input
• Neck Proprioceptors
• Proprioceptive and exteroceptive information from other parts of the body.
• Neuronal connections of vestibular apparatus with CNS.
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PATHWAY FOR EQUILIBRIUM REFLEX
• Initiates in vestibular verves.
• Then passes to vestibular nuclei and cerebellum.
• Next signals are sent to reticular nuclei of brain stem as well as down the spinal chord by way of vestibulospinal and reticulospinal tracts.
• Antigravity muscles may be stimulated or inhibited.
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Thank You