Sunday, August 18, 2013

The sensory system part one, Introduction.

Your child’s sensory motor system is a very important part of his development. In fact, almost all human activity is based in the sensory motor system. Basically, we take in information through our senses and then we react to it, usually with a motor response of some sort.  The system is very complex and there is coordination (it is a pre internet type of web) among all the senses and the motor systems of the body but I will try to keep it simple here. Something happens in the environment and the sense organs pick it up. The “sensation” is transmitted to the brain where it is processed (and coordinated with other information from other senses) interpreted and a response is formulated. This information goes to the motor cortex of the brain where instructions to your body are transmitted and you react. All this takes place in nanoseconds so your response may seem immediate, certainly much faster than it took to read about. Let’s use a hot iron as an example. Your finger touches the iron and the pain and thermal sensors in your finger recognize the sensation. It is sent to the brain which registers “HOT” and dangerous. The information is sent to the motor areas of the brain which determines that your muscles in your arm must activate to move your finger away from the danger. This information is sent to your finger and you pull your finger away from the iron. Most of us have had this experience so you know how fast this system works.
In looking at the sensory part of this system we need to understand what the senses are. Firstly, the system consists of three basic parts, the sensory receptor, the nerve transmitter and the part of the brain that processes the sensation. The receptors are the organs that come in contact with the sensation, the nerve endings throughout the body and especially around the head that receive the sensation.  The nerves are the transport system, much like telephone cables that transmit the sensation to the brain. All of the understanding of what was sensed takes place in the brain. Each sense is processed in its own part of the brain separately, although there are connections so that this information can be coordinated to form a whole picture. This interconnection also helps when there is an impairment in one of the senses, such as blindness, which allows information from other senses to help “cover” for the impaired sense in gaining a better picture of the environment.
Most of us have heard of the five senses. Many of us have heard the term the sixth sense used to refer to unexplained abilities.  Well, the truth is that we have more than 5 senses so that expression is going to have to change to the 10th sense or something like that.
The first 4 senses are special senses, so called because they have a single sense organ and detect a single type of sensation.  These are sight, hearing, smell and taste.  Each of these has a specific sensory receptor located around the head.  For sight it is the eyes, for hearing it is the ears. Smell and taste are quite related and are often called the chemosenses. 
The remaining senses are called the somatosenses because they affect the body as a whole. These include touch, which is really several senses combined under one name, the proprioceptive sense and the vestibular sense. The first two have sense receptors spread throughout the body while the vestibular sense uses some of the same structures in the ears that are used for hearing.

In the next few articles, I will look at the development of each sense both in terms of the development of the structures and of the sense itself. Most of the sense organs develop in the absence of stimulation but processing continues to develop with experience and, in later years , many of the senses become weaker due to changes in the structures. After looking at each sense in depth I would like to discuss sensory processing and the area of sensory processing dysfunction, which is in the process of becoming a diagnosis as well as being a symptom in several other disorders, including autism.

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