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