The vestibular system is the system that tells you where your body is in relation to the earth. Gravity works on the proprioceptive system and the vestibular system. This is how you understand right side up and upside down. It is also why you get dizzy when you spin around in circles. While the vestibular system reacts to the body as a whole its receptors are not spread throughout the body as with touch and proprioception. They are located in the ears in the semi-circular canals. These canals are filled with fluid which sloshes around in them as the body moves through space. There are many fine hairs located around the canals and these are the vestibular receptors. As the fluid sloshes on them they activate and send messages to the brain that tells you that you are moving. Ear infections and colds can therefore affect both the vestibular sense and the sense of hearing because they are taking place in the organ responsible for both senses.
The Sense of Balance
Balance is not a true sense but rather a combination of information from the vestibular system, the proprioceptive system and the visual system. The vestibular system is key in this as it tells the body about its position relative to gravity. It lets you know if you are right side up or upside down. This system alerts your body if you start to fall. The proprioceptive system plays a role in that it helps you organize your body so you do not fall and we use visual cues to help orient ourselves to the upright position. Balance can be maintained without visual cues but they make it easier. Balance in different positions develops after the baby can achieve the position. Once baby is sitting, he is unsteady at first and then develops the balance reactions he needs to remain sitting. The same is true for hands and knees and for standing. The balance reactions are geared towards keeping baby upright. They come into play when your center of gravity is pushed off center. They include tightening of the trunk muscles and extension of the arm and leg on the side opposite the fall in an attempt to pull you back into “balance”. If that fails, protective reactions come into play. This is where you fling out your arms to catch yourself. These responses are automatic and triggered by the sensory input of your vestibular system that you are about to fall.
These last 7 articles are a description of the senses. They have been getting a lot of publicity because there are times when they do not function smoothly. As we stated, almost all human activity has a connection to the sensory motor arc. Therefore, dysfunction in this system can affect many aspects of life. Some learning disabilities have been connected to problems in this system. Certain types of social emotional issues are connected to issues with sensory processing. While not part of the definition of Autism, many autistic children respond well to treatment of sensory issues indicating that this may be a component to this disorder. The evidence is building that appropriate sensory processing is an important part of development.