Sense of balance
In the vestibular system, equilibrioception is determined by the level of a fluid called endolymph in the labyrinth, a complex set of tubing in the inner ear.
Balance can be upset by Ménière's disease, superior canal dehiscence syndrome, an inner ear infection, by a bad common cold affecting the head or a number of other medical conditions including but not limited to vertigo.
Each semicircular canal (SSC) is a thin tube that doubles in thickness briefly at a point called osseous ampullae.
The cupula is a gelatin bulb connected to the stereocilia of hair cells, affected by the relative movement of the endolymph it is bathed in.
[citation needed] After any extended rotation, the endolymph catches up to the canal and the cupula returns to its upright position and resets.
When extended rotation ceases, however, endolymph continues, (due to inertia) which bends and activates the cupula once again to signal a change in movement.
Otolithic organs have a thick, heavy gelatin membrane that, due to inertia (like endolymph), lags behind and continues ahead past the macula it overlays, bending and activating the contained cilia.
The inferior olivary nucleus aids in complex motor tasks by encoding coordinating timing sensory information; this is decoded and acted upon in the cerebellum.
The vestibulocerebellum regulates eye movements by the integration of visual info provided by the superior colliculus and balance information.
It receives input from the trigeminal nerve, dorsal column (of the spinal cord), midbrain, thalamus, reticular formation and vestibular nuclei (medulla) outputs[clarification needed].
Lastly, the cerebrocerebellum plans, times, and initiates movement after evaluating sensory input from, primarily, motor cortex areas, via pons and cerebellar dentate nucleus.
The superior colliculus (SC) is the topographical map for balance and quick orienting movements with primarily visual inputs.
[19] Equilibrioception in many marine animals is done with an entirely different organ, the statocyst, which detects the position of tiny calcareous stones to determine which way is "up".
