Balance

• The chief role of the vestibular system is to detect angular and linear accelerative forces. The semi-circular canals detect and respond to movement and change of direction; the utricle and saccule detect and respond to change of head position and gravitational pull. Thus the vestibular system perceives movement and changes in the position of the head; it can tell a person if his head is upright or if it's tilted, even if his eyes are closed. The vestibular system influences a person's sense of equilibrium.
  
  The vestibular receptors process information having to do with acceleration and intensity of movement. A person with an intact vestibular system experiences this every time he takes a car ride. If the driver is a relatively experienced one, everything goes smoothly. However if, for example, one is riding with a student driver who accelerates rapidly and brakes just as rapidly, after a while this rapid acceleration and deceleration causes the vestibular system to become over-aroused. Nausea or some other autonomic sign may be the result.
  
  

Coordination

• The vestibular system processes the information it perceives about the position of the head in relation to the rest of the body and sends it to many different parts of the brain. The brain then coordinates this information with the other sensory systems of the body--the eyes, muscles, joints, palms and fingertips, pressures on the soles of the feet and the gravity receptors on the skin.
  
  The brain uses this information to stabilize the eye muscles during head movements, allowing the body to maintain a stable visual field and image. A person is then able to coordinate eye movements with head movements. For example, the student can look up to the classroom blackboard and back down to his notebook with ease, and a tennis fan can turn his head to follow the movement of the ball from one side of the court to the other.
  
  With the sensory systems cooperating due to the information provided by the vestibular receptors, a person is able to maintain a center of gravity while standing upright and to maintain balance, even as he moves through space. He can coordinate motor skills for both sides of his body, enabling him to ride a bicycle or cut with a pair of scissors.
  
  

Other Functions

• The vestibular system also helps in the development and maintenance of normal muscle tone. Muscle tone allows a person to hold his body in position and to maintain that position. Just keeping your head up requires muscle tone.
  
  Another way the brain uses the information received from the vestibular system is to adjust a person's heart rate and blood pressure during changes in posture--for example, when standing to an upright position after a period of lying down.
  
  The vestibular receptors manage a person's arousal or alertness levels, determining how long a person can maintain focus. For example, when a person with normal vestibular function feels the need to increase alertness, he simply gets up and moves around. For a person with an under-responsive vestibular system, this would be insufficient. He would need intense movement to increase alertness, such as jumping on a trampoline or hanging upside down or spinning around in order to arouse himself to alertness.