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| | ===[[Vestibular System Examination]]=== | | ===[[Vestibular System Examination]]=== |
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| − | ====The Vestibulocochlear Nerve====
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| − | * Cranial nerve VIII is the vestibulocochlear nerve.
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| − | * The vestibulocochlear nerve carries
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| − | ** Auditory, or cochlear, signals.
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| − | ** Balance, or vestibular, signals.
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| − | * Signals from CN VIII are relayed to the vestibular nuclei in the brainstem.
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| − | ** The nuclei in turn relay information to
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| − | *** The eyes
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| − | *** The body and limbs
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| − | *** Higher centres.
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| − | * Many efferent signals are controlled in part by cerebellar input.
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| − | ====Unilateral Vestibular Disease====
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| − | * Horses with unilateral vestibular lesions often have a head tilt towards the side of the lesion.
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| − | * If nystagmus is absent, determining whether a horse with a head tilt is also weak is helpful in deciding whether vestibular disease is central or peripheral.
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| − | ** In peripheral diease, the horse may be ataxic but weakness is not normally seen.
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| − |
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| − | =====Acute=====
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| − | * In the acute stages of vestibular disease, spontaneous nystagmus may be present.
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| − | ** The appearance of nystagmus is different depending on the type of vestibular disease present.
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| − | *** Central vestibular disease
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| − | **** Nystagmus often is variable; i.e. rotary, horizontal and vertical.
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| − | *** Peripheral vestibular disease
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| − | **** The fast phase of the nystagmus is away from the side of the lesion.
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| − | =====Chronic=====
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| − | * Nystagmus may resolve in more chronic lesions.
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| − | ** However, it may return with changes in head position.
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| − | *** I.e. positional nystagmus.
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| − | * Visual accomodation improves ataxic movements.
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| − | ** However, these may return dramatically on blindfolding.
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| − | ====Bilateral Vestibular Disease====
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| − | * An observable head tilt may not be present.
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| − | * Movements are likely to be markedly ataxic.
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| − | ** This is probably due in part to involvement of ascending proprioceptive and descending motor pathways that run through the brainstem.
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| − | [[Category:Cranial Nerve Examination - Horse]]
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| | ===[[Pharyngeal and Laryngeal Function]]=== | | ===[[Pharyngeal and Laryngeal Function]]=== |