The Human Balance System consists of three parts. The Visual (depth, velocity and motion perception), the Vestibular System (inner ear), and the Somatic Sensory or Somatosensory System (proprioception and exteroception).
Vestibular System (inner ear) - The most important part of human balance is the inner ear which contains three canals. In simple terms, the three canals contain a gel-like liquid called endolymph and tiny hair cells. When both inner ears are working properly they give the brain information through the central nervous system about linear and angular positions of the body with respect to gravity.
Visual (depth, velocity and motion perception) - Visual input from the eyes send the brain information about the position of the body relative to other objects, their depth, velocity and motion. The eyes and the ears compliment each other not only to maintain balance, but also to maintain clear vision during movement. The inner ear sends impulses that continuously adjust your eyes in coordination to even the smallest movement of the body such as your heartbeat or breathing.
Somatic Sensory or Somatosensory System (proprioception and exteroception) - The Somatosensory System provides the brain two valuable pieces of internal and external spatial information to maintain balance. One comes from internal sensors within the body called propriceptors. Proprioceptors give the central nervous system information about the movement of body parts in relation to other parts of the body. This is called the sense of proprioception. Without the sense of proprioception, you would not be able to put food in your mouth without visually watching your hand moving to your mouth. A common test for loss of proprioception is walking the line during a sobriety test by police officers.
The other Somatosensory information the brain uses comes from external body sensors called exteroceptors. Exteroceptors are pressure sensors located in your feet and hands that provide external spatial information about the topography of the ground or support surface. Exteroception also helps in your overall balance system by relaying information about ground movement. An example would be the difference between standing on solid ground and sinking into mud.
By: Rick Contrata