The Vestibular System
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Transcript of The Vestibular System
The Vestibular System
Csilla Egri, KIN 306 Spring 2012
Will Ferrell and Jon Heder are challenging their vestibular systems
Outline
Vestibular system Function Structure
Semicircular canals Sensory transduction
Otolith organs Vestibular pathways Vestibular reflexes
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Vestibular System: Function3
Detects angular and linear acceleration Important in maintaining balance, posture, and
vision Connections with brainstem, cerebellum, and
somatic sensory cortices to provide info about the motions & position of the head & body
Vestibular System: Structure4
Vestibular System: Structure5
utricle
saccule
Otolith organs
Semicircular canals: structure6
each semicircular canal contains an ampulla Contains hair cells
embedded in sensory epithelium called crista ampullaris
Cilia of hair cells project into gelatinous cap called cupula
Enlargement of ampulla
Crista ampullaris
Semicircular canals
Semicircular canals: function
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Specialized for responding to rotational acceleration of the head
Head rotation results in intertial movement of endolymph in opposite direction
Bends cupula which bends hair cells
Same mechanical/electrical coupling as in auditory hair cells
Excites/suppresses release of NTs from hair cells depending on direction of movement
B&B Figure 13-18
Semicircular canals: sensory transduction
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B&L Figure 8-26
Steriocilia maintain directionality on both sides of the head Bending towards kinocilium opens mechanically gated cation
channels K+ influx depolarization Bending away from kinocilium closes channels that are open
during resting state hyperpolarization
Semicircular canals: sensory transduction
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Kandel Figure 40-7
Paired canals work together to signal head movement
With turning of the head, hair cells on one side of the body send excitatory signals to the brain while hair cells on the opposite side are inhibited
Otolith Organs: Structure10
Two otolith organs; utricle and saccule
Each contains a sensory epithleium called the macula
Horizontally oriented in utricle
Vertically oriented in saccule
cilia of hair cells embedded in gelatinous otolithic membrane
Embedded on surface are calcium carbonate crystals called the otoliths
otoliths
Otolith Organs: Function11
Specialized to respond to gravity and linear acceleration Otoliths have a higher density than endolymph
Shift when angle of head changes Causes otolithic membrane to shift in same direction Cilia of certain hair cells deflected
Excites/suppresses release of NTs from hair cells depending on orientation of cilia
Otolith Organs: Function12
kinocilia of each hair cell are oriented in different directions in relation to striola Utricle: towards striola Saccule: away from striola
striola
Otolith Organs: Function13
Same sensory transduction as semicircular canals Bending of cilia towards
kinocilium depolarizes the hair cell
Kandel Figure 40-3
otoliths
Is this a picture of a macula from the utricle
or saccule?
Vestibular Pathways14
vestibular afferents synapse on vestibular nuclei located in medulla & pons Nuclei integrate information from vestibular, visual, and somatic receptors and send
collaterals to 1.cerebellum
Sends corrective adjustments to motor cortex: maintenance of balance and posture
Vestibular Pathways15
2.nuclei of cranial nerves Control coupled movements of the eyes, maintain focus and visual field
3.nuclei of accessory nerves Control head movement and assist with equilibrium
Vestibular Pathways16
4.ventral posterior nucleus of thalamus and vestibular area in cerebral cortex (part of primary somatosensory cortex)
Conscious awareness of the position and movement of head
Areas 1,2,3
Vestibular Reflexes17
Vestibulospinal Reflexes Senses falling/tipping
contracts limb muscles for postural support Vestibulocollic Reflexes
acts on the neck musculature to stabilize the head if body moves
Vestibulo-ocular Reflexes stabilizes visual image during head movement
causes eyes to move simultaneously in the opposite direction and in equal magnitude to head movement
Vestibulo-Ocular Reflex (VOR)18
Example: head movement to the
LEFT
1. inertia of endolymph movement to the right in horizontal vestibular canals causes:
a ’d firing of left vestibular afferent
b ’d firing of right vestibular afferent
2. Excitatory connections with contralateral abducens nuclei and inhibitory connections to ispilateral side
3. Excitatory connection to inhibitory interneuron in contralateral vestibular nuclei
4. Movement of the eyes to the right
abducens nuclei
occulomotor nuclei
vestibular nuclei
B&L Figure 9-27
Objectives
After this lecture you should be able to: Relate the anatomical organization of the semicircular
canals and otolith organs to sensation of movement/acceleration Describe the mechanism of sensory transduction in these
structures Outline the vestibular pathways and projections to
various brain regions Describe the pathway of the horizontal vestibulocular reflex
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1. What specific part of the vestibular system would sense
1. Movement in an elevator2. Abrupt stop of a moving vehicle3. Shaking your head side to side
2. In the utricle, if hair cells bend away from the striola, will this cause depolarization or hyperpolarization of the receptor?
3. Based on what you know about the vestibular system, if you spin around for 5-10 seconds, why do you feel dizzy even after you stop?
Test your knowledge