Vestibular system & Balance

Vestibular system & Balance 1. Identify on diagrams the following structures of the vestibular apparatus: lateral (horizontal), anterior (superior), posterior semicircular canals, utricle, saccule, vestibular nerve. = fluid in bony labyrinth

Anterior (superior) semicircular canal Lateral (horizontal) semicircular canal

= fluid in membranous labyrinth

Posterior semicircular canal Vestibulocochlear nerve SEMICIRCULAR CANALS -

Loops portions Contain AMPULA o Ampulla = bulge in duct wall o Ampulary crests = areas in semicircular canal  The receptors

NOTE THAT ALL RECEPTORS ARE HAIR CELLS OTOLITH ORGANS -

Utricles Saccules Receptors in these are referred to as maculae

2. Briefly describe how the receptors in a semicircular canal are activated. - Ampulla o Bulge in the membrane allowing for hair cells to be located o Hair cells respond to mechanical displacement  HAIR CELL  connects to afferent neuron and sits in supporting cell  KENOCILIA  each hair cell has one large kenocilia  STEREOCILIA  each hair cells has 40-70 stereocilia o

 CUPULA  gelatinous substance within which kenocilia and stereocilia sit RECEPTOR ACTIVATION:  Any movement of the cupula results in movement of the kenocilia and stereocilia  stereocilia are moved towards the kenocilia o stimulation; increased AP o Gi es perceptio e’re lea i g to that side  If the kenocilia are moved towards the stereocilia o Hyperpolarisation; decreased AP o Gi es the perceptio e’re lea i g a ay fro that side

-

Vestibular branch from receptors Cochlear branch for auditory functions

3. What would be the consequence if neural input from the semicircular canals on one side of the head was blocked? NORMAL SEMICIRCULAR CANAL FUNCTION o

o

o

-

Vertical stance  Tonic levels of afferent input from both sides of semicircular canals remain the same  Vertical position perceived Tilted left  Increased rate of afferent input on left side  Decreased rate of afferent input on right side  Leaning to the left perceived Tilted right  Increased rate of afferent input on the right side  Decreased rate of afferent input on the left side  Leaning to the right perceived

BLOCKED SEMICIRCULAR CANAL o Vertical stance  Decreased levels of tonic afferent input on affected side  Unaffected side has comparatively higher afferent input  Leaning towards unaffected side perceived  Postural response to sway back towards affected side  falls risk o Tilting to affected side  Decrease levels of tonic afferent input on affected side  Unaffected side has decreased afferent input, but still not lower than affected side  Leaning towards unaffected side perceived o

 Postural response to sway back towards affected side  falls risk Tilting to unaffected side  Increased levels of tonic afferent input on unaffected side  Affected side has comparatively lower afferent input  Leaning towards affected side perceived  Postural response to sway back towards affected side