The ability to stand upright and move without falling over depends on our sense of balance. Structures in the inner ear, known as the vestibular apparatus, contribute to balance by detecting the position and movements of the head. The vestibular apparatus is composed of three semi-circular canals and the two-chambered vestibule.
The role of hair cells
The head’s movements are detected by hair cells found in structures called cristae in the semicircular canals and in two structures called maculae in the vestibule.
Linear movement and static position
The two maculae within the vestibule of the inner ear sense linear movements – for example, when travelling by car or using a lift – and the orientation of the head relative to gravity. Detecting the head’s position in relation to gravity helps us, for example, to know instantly which way is up when we dive into deep water.
Rotational movements of the head are detected by the cristae in the fluid-filled semicircular canals. The three semicircular canals are at right angles to each other, so head rotation in any direction is detected by at least one canal. The information is used both to maintain balance and to keep vision stable when the head moves.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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