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24 September 2014
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Nervous system - Balance

Inner ear: Contains your organs of balance

Two organs of balance: Detect the position and rotation of your head

Other balance sensors: Your eyes and receptors in your muscles and tendons

Spinning head: Occurs when the balance sensors in your ear are disrupted

In your ears

Your ears aren't only your organs of hearing. They also help you keep your balance. In your inner ear is a maze of bony chambers called the bony labyrinth, which can be divided into three parts. One section, known as your cochlea, is responsible for your sense of hearing. The other two, however, contain your organs of balance.

Position of your head

Your first organ of balance detects the position of your head. It consists of two sacs called the utricle and saccule. Within these sacs are receptors called maculae. They are made of sensory hair cells covered by a gel-like cap with tiny crystals inside. Whenever you tilt your head, gravity causes the crystals to slide to one side, creating a pull on the gel and the sensory hairs. This triggers your hair cells to fire nerve impulses along your vestibular nerve to your brain.

Rotation of your head

Your second organ of balance detects rotational movements of your head. It consists of three fluid-filled loops that are arranged at right angles to each other. Within each of these 'semicircular canals' is a receptor region called crista ampullaris. It is made of hair cells covered by a gel-like cap. When you begin to rotate your head, the fluid in the canals lags behind and moves in the opposite direction, thereby bending the gel-like cap. This stimulates your hair cells, which, in turn, fire nerve impulses along your vestibular nerve to your brain.

Other balance sensors

To keep your balance, you don't only rely on the two sensory organs in your inner ear. Your eyes also deliver important information about your body's position, as do receptors in your muscles and tendons. Called 'proprioreceptors', they detect how stretched your muscles, tendons and joints are.

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