Organs of Balance

The organs of balance which influence the action of the cerebellum, are located in the inner ear adjacent to the organs of hearing. The position of the three semicircular canals and the saccule, the utricle and the endolymphatic duct are shown in relation to other structures in the inner ear. A cross section of the semicircular canals, which consist of three tubes, are positioned at right angles to each other in different planes. They are filled with a fluid known as endolymph. In the base of each semicircular canal are hairlike receptors. Any movement of the head causes the fluid within the canals to move and so stimulate the receptors to send information to the brain about the direction of the particular movement that has occurred. The utricle and saccule contain receptor cells with tiny stones of calcium carbonate-otoliths. The otoliths are relatively mobile and movement of the head causes them to move. This changes the pressure that they exert on the receptors, which then send information about the direction of the head's movement to the brain, and illustrate the three planes of movement in which the head and body can move to stimulate the receptors in the semicircular canals.

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