the

The Vestibular System: The Brain and Balance

my name is Steve Lewis burger I'm

neuroscientist I'm the chair of the

Department of Neurobiology at Duke

University the vestibular system is a

set of sensors inside our ear near were

we in in in the temporal bone and they

are exquisitely sensitive to our motion

through space and our position with

respect to gravity so if I tilt my head

this way those sensors indicate that my

head is tilted to the left if I turn my

head like that those sensors indicate

that I turned my head to the right it's

important for us to be exquisitely aware

of our position in space and if you

think about if you slip on the ice or

trip over a step when you're climbing

the very first thing that happens is you

put out your hand to try to prevent

yourself from falling and hitting your

face and that's driven by the vestibular

system it's sensitive to when you start

to fall and it immediately with very

after very short times on the orders of

fractions of a second it causes your

motor system to take actions that will

rescue you from serious damage the

primary sensory cell is a hair cell and

it basically is a cell that has little

cilia sticking out of it and the way it

works is that if the cilia Bend then the

electrical potential of the cell changes

and that creates that that transforms a

mechanical signal into an electrical

signal and the electrical signals are

the currency of the brain now different

parts of the vestibular system use those

hair cells in different ways and so

there's a simple mechanical system

that's a tube like a doughnut and it has

the hair is sticking out into it so that

when you turn the tube the hairs this

fluid inside that tube deflects the

hairs and so that's how we're sensitive

to our head turns and then the other two

organs are quote their two organs called

the otolith organs

they basically have the hair sticking

out into a rock and if I tilt my head

back like that the rock slides back it

pulls on the hairs and it takes a

mechanical event turns it into an

electrical signal so that the brain can

use it

we know that motion sickness is caused

when where your vestibular system is

telling your brain is different from

what your visual system is telling your

brain we do not know exactly how that

works and we don't even know why we

would have motion sickness there are

some just-so stories we do know that the

middle midline of the stimulus

cerebellum is important for motion

sickness but I guess I would point out

that I get motion sick when I'm on a

boat and when you're on a boat and

you're in the waves and you're rolling

back and forth very slowly that seems to

be the kind of stimulus that when it

doesn't match with what you're seeing

creates the sensation of motion sickness

and nausea and you think about our

astronauts it was not widely publicized

but our astronauts were motion sick for

the first at least three to five days

that they were in orbit because without

gravity the system that senses where

gravity is and your head position in

space no longer functions and so they

had completely lost that part of the

vestibular input that tells them whether

they're tilting their head or whether

they're looking whether whether whether

you know that's down or that's down and

so there's a complete loss of the

matching of what they're seeing and what

they're feeling from their their

vestibular system so they were they were

really quite miserable

vertigo is when your vestibular system

isn't is giving you a wrong signal and

so it's telling you that you're moving

when you're not and so you might get the

sensation that you're just turning

around in a circle or you might get the

sensation that you're falling this way

and that comes from you know a part of

the vestibular system being broken

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it's an incredibly simple reflex

behavior that is really important to us

and many animals so the job of the

visual system is to process images so

that you can see what's happening and if

images slip of move a little bit and the

eye doesn't move to track them then they

slip across the retina and we're not

capable of processing and processing

them with nearly the same acuity and so

the vestibular ocular reflex is a reflex

that uses our head turns to guide our

movements and if I turn my head back and

forth like this my eyes keep looking

directly at you and that's that would

happen if I had closed my eyes and we're

in the dark

that's the vestibular ocular reflex

making sure that my eyes remain sort of

like gyroscopically stabilized so that

even as I move my head around the place

I'm looking is nice and stable and so

the images that are coming from the

external world don't slip across my

retina and I have a good vision

I'm Steeve less burger and I'm a

neuroscientist

you

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