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Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics
in 2 minutes or less.
In this installment I will discuss the vestibular system.
The vestibular system is a sensory system responsible for providing our brain with information
about motion, head position, and spatial orientation; it also is involved with motor functions that
allow us to keep our balance, stabilize our head and body during movement, and maintain
posture.
The main components of the vestibular system are found in the inner ear in a system of
compartments called the vestibular labyrinth, which is continuous with the cochlea.
The vestibular labyrinth contains the semicircular canals which are three tubes that are each
situated in a plane in which the head can rotate.
Each of the canals can detect one of the following head movements: nodding up and down, shaking
side to side, or tilting left and right.
The semicircular canals are filled with a fluid called endolymph.
When the head is rotated, it causes the movement of endolymph through the canal that corresponds
to the plane of the movement.
The endolymph flows into an expansion of the canal called the ampulla, within which there
are hair cells, the sensory receptors of the vestibular system.
At the top of each hair cell is a collection of small "hairs" called stereocilia.
The movement of the endolymph causes movement of these stereocilia, which leads to the the
release of neurotransmitters to send information about the plane of movement to the brain.
The vestibular system uses two other organs, known as the otolith organs, to detect forward
and backward movements and gravitational forces.
There are two otolith organs in the vestibular labyrinth: the utricle, which detects movement
in the horizontal plane, and the saccule, which detects movement in the vertical plane.
Within the utricle and saccule, hair cells detect movement when crystals of calcium carbonate
called otoconia shift in response to it, leading to movement in the layers below the otoconia
and displacement of hair cells.