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Borrowed from >>>> http://vestibular.org/understanding-vestibular-disorder/human-balance-system

GOOD BALANCE IS OFTEN TAKEN FOR GRANTED.

Most people don’t find it difficult to walk across a gravel driveway, transition from walking on a sidewalk to grass, or get out of bed in the middle of the night without stumbling. However, with impaired balance such activities can be extremely fatiguing and sometimes dangerous. Symptoms that accompany the unsteadiness can include dizziness, vertigo, hearing and vision problems, and difficulty with concentration and memory.

WHAT IS BALANCE?

Balance is the ability to maintain the body’s center of mass over its base of support.¹ A properly functioning balance system allows humans to see clearly while moving, identify orientation with respect to gravity, determine direction and speed of movement, and make automatic postural adjustments to maintain posture and stability in various conditions and activities.

Balance is achieved and maintained by a complex set of sensorimotor control systems that include sensory input from vision (sight), proprioception (touch), and the vestibular system (motion, equilibrium, spatial orientation); integration of that sensory input; and motor output to the eye and body muscles. Injury, disease, or the aging process can affect one or more of these components.

SENSORY INPUT

Maintaining balance depends on information received by the brain from three peripheral sources: eyes, muscles and joints, and vestibular organs (Figure 1). All three of these sources send information to the brain in the form of nerve impulses from special nerve endings called sensory receptors....

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