Vestibular sense and sense of Balance

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.  

Proprioception

The word proprioception means responding to one’s self. This is the sense that allows you to understand what your body is doing in relation to itself. If you are told to raise your hand, you understand that your hand is raised even when your eyes are close.  That is proprioception.  Another example of proprioception is the test police use to test for drunk driving where they ask one to close one’s eyes and touch one’s nose. You can do this because of proprioception.

The nerve endings for this sense are located at every joint and in the muscles (muscle spindles) throughout the body.  Proprioception develops in tandem with touch and the receptors are in place in very early fetal development. Infants rely on conscious proprioception a lot as they are learning new skills and learning to control their bodies. This process is teaching their proprioceptive sense to function on its own. 

One reason that proprioception is not thought of as one of the “senses” is because it functions mostly on an unconscious level. We are usually most aware of it when learning a new motor task and then , when learned, don’t think about the proprioceptive input anymore. In fact, if we did, our movements would be labored and choppy. The article cited at the end of this section includes a description of a man who lost his sense of proprioception and the difficulties he faced in trying to do simple motor tasks.

Putting increased weight on the joints increases the sense of proprioception. Stimulating proprioception is both calming and alerting (like chocolate, which both calms and alerts, as few other things do). This is why a hug feels so good. Aside from the social meaning, a hug stimulates the proprioceptive system.  Proprioception has been receiving attention as it seems in recent years as it seems to be critical in the work with and treatment of disordered sensory processing.

Kinesthesia is the sense of the movement of your body. It seems to use the same system as proprioception but may be processed in a different part of the brain. It was the study of kinesthesia that led to the discovery of the sense of proprioception

.http://serendip.brynmawr.edu/exchange/node/1699 

THE SOMATOSENSES Touch

Touch is not really one sense. It is made up of several different senses which have different nerve endings and different response areas in the brain. In other words, they are processed individually though we lump them all together and call them touch.  These include light touch, deep pressure, heat , cold  and pain receptors. What they have in common is that the nerve endings are spread throughout our skin so we can experience sensation from any part of our body. There are some areas that have a higher concentration of nerve endings and are therefore more sensitive than other areas of the body. Some areas of the body may have more of one kind of receptor than others so may be more sensitive to certain types of touch than to others but in general there are touch receptors all over the body in the skin. Some types of receptors are around the internal organs as well. We all know you can have a stomach ache that is not felt from the skin. All of this is complicated by the fact that you may have different touch sensations at different places at the same time. You mind needs to sort all the sensation and let you decide which is the most important for you to get the information that you need.  If you remember, in the introduction to this series, we used the example of the hot iron to illustrate the sensory motor arc. That example uses the sense of touch, specifically, heat, so you can see how fast your brain can select what you need to know.

The sense of touch is one of the earliest to begin to develop, with some receptors in place by 4 weeks gestation, but it seems to take up to 16 to 20 years for the system to be fully operational.  There are at least 4 different  types of receptors and miles of nerve fibers, as well as the cognitive learning needed to distinguish from what one thing feels like as opposed to another. The fact that you can reach into your purse and find the keys without looking is a testament to the development of your sense of touch.

Simple touch is anything but! The simplest sensation is pressure, but as noted, light pressure and deep pressure are registered differently. Next would come vibration, followed by recognition of different textures, sizes, shapes and spatial orientation, which can all be recognized by touch.  Research indicates that awareness of pressure and vibration is present at birth. Size recognition seems to begin early, perhaps 2-4 months but is on a basic level and need refining. There is some recognition of different textures by 4-6 months which continues to be refined over the next 10 years. The recognition of shape difference by touch may begin after 6 months and there are indications that this, too, continues to develop during childhood.

Early tactile exploration is often by mouth, as this is a very sensitive area for touch stimulation. Manual exploration actually begins around 4 months of age and continues to improve through childhood. The ability to recognize objects by touch is pretty much the same from 15 to about 50 years of age but as with other senses, there is a decline during the aging process,  just as touch is one of the first senses to develop it is the last to decline.

Touch is probably the most pervasive sense we have. It is everywhere in our bodies and is difficult to occlude. Just as development impact the sense of touch (learning shapes, textures etc.), there is ample evidence that touch impacts development.  Studies of infants who were deprived of a chance to use their sense of touch, who were not held or whose physical contact was limited to the crib they were lying in, suggest that this caused global delays that were difficult to make up. Of course, the sense of touch, along with the next two we will discuss, underlies all motor abilities

. http://www.scholarpedia.org/article/Development_of_touch   

http://www.livestrong.com/article/508221-the-influence-of-touch-on-child-development/   http://library.thinkquest.org/05aug/00386/touch/sensoryreceptors.htm

Vision

Sight is one of the most complex senses. The eye structure is developed in the first 24 weeks of pregnancy but the eyelids may be fused until 26 weeks and the lenses are cloudy until about 4 months after birth. The rods develop between 28 and 34 weeks and then the development of the cones begins. The rods are light sensors and allow your eyes to adjust to variations in light. They also help with peripheral vision (seeing out of the side of your eye). The cones are what allow us to see colors.  The eyes continue to develop until your child is around 3 years of age.

Vision takes a large area of the brain at the back. This area develops before the baby is born in the absence of stimulation (Usually by 34 weeks).  At birth, your baby can see at close range. The best focus is at about 8 to 10 inches from their eyes (20-25 cm). Babies can see color but early on they can see strong contrast much better. They show a preference for looking at simple geometric patterns in two contrasting colors in the first 2 months. By around 3 months, babies are more interested in faces (both real and in photos or drawings) and pay attention to more variations in color. At around 4 months, the lenses clear and baby can now focus beyond the 8-10 inch range. This is often very noticeable, especially during feeding, because all of a sudden the baby is looking all around and not focused on the task at hand.  He has just discovered a whole new world.

Vision not only involves seeing with the eyes but the ability to move the eyes in coordination. The perception of depth and the use of eye hand coordination rely on the movement of the eyes. In the first two months a baby may appear cross eyed at times but by 5 months the muscles of the eyes should be strong enough that a baby can move the eyes together to smoothly follow a moving object across, up and down and in a circle as well as to guide their hand to reach and hit an object. When babies begin to crawl, these skills develop even further. Babies first learn about depth by looking and reaching for objects that are at different distances. Although there is some concept of depth in the first few months , this learning really takes off in the second quarter (4-6 months). As baby becomes more mobile from 6-12 months, he learns more about depth and can begin to understand it better.    Visual skills continue to develop until 6 or 7 years old.

Babies eyes should be protected. They are very sensitive to light in early infancy and should be shielded as much as possible from harsh strong light in their eyes. It is never too soon to begin to use sunglasses on infants who are out in strong sunlight. If your baby is not moving his eyes smoothly to follow an object or

continues to have crossed eyes after 5 months, you should mention this to your doctor. If there is some problem, it is easier to solve if it is caught earlier and it will help in the continued visual development that takes place.

http://www.aoa.org/patients-and-public/good-vision-throughout-life/childrens-vision/infant-vision-birth-to-24-months-of-age

http://www.perceptionsense.com/2012/11/post-2-visual-cliff-experiment-for.html 

The development of hearing.

Hearing is one of the later senses to develop.  It seems to start at 23 weeks gestation.  The first responses to sound at the brainstem level are around 24 weeks gestation.  The structures for hearing continue to develop between the ages of 24 and 34 weeks gestation. 

It has been noted that babies do hear while still in utero. When babies are born, they seem to recognize their mother’s voice. Dr. Barry Brazelton used to do an exercise with babies that were hours old. He would hold the baby between its mother and another person and ask both to speak at the same time. The baby would invariable turn towards its mother’s voice. He did the experiment with the father as well and the babies overwhelmingly turned towards their father over a stranger. The uterus is a noisy environment however and sound must travel through liquid as well as distractions so the baby probably hears a more distorted sound from outside while hearing the mother’s voice from inside. Babies in utero respond to different types of music according to research indicating that it may be worthwhile to play music to the developing baby. At birth, the hearing system is in place though babies are better able to hear higher frequencies at first, which may also account for their higher receptiveness to a female voice. The ability to recognize the meanings of sounds comes with experience so the system continues to develop after birth as well. There is research that shows that babies are tuned to the sounds of language and music over random noise sounds.  They listen more acutely and for longer to organized sounds than to random sounds according to studies. There is no question that babies learn to speak by what they are hearing. This accounts for the fact that children use the same accents of those around them.

Again, as with other senses, the structures in the ear may be damaged or may just wear out as one becomes older and we find many elderly people needing assistance to hear. 

http://www.edu-cyberpg.com/Literacy/whatresearchwomb.asp

http://birthpsychology.com/free-article/importance-prenatal-sound-and-music

http://www.plu.edu/news/2012/12/infant-language/)

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 10^th 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.