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 

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 Special Senses, part 1- the Chemosenses, gustatory and olfactory, aka taste and smell

Smell may be the least neurologically complex system of the sense as the information from the smell sensors in the nose have a direct link to the processor in the brain. Taste is considered one sense but in fact there are 5 specific receptors (located on the tongue in areas) for salty, sweet, tart, sour and what is being called “meat” flavors. These five flavors are given more variety by the sense of smell which distinguishes variations within these five flavors of foods. Often, in high school biology class, teachers do an experiment where they stop the sense of smell and offer a bite of an apple and of an onion to a student. Without smell the student cannot tell which is which as the texture is similar and both are sweet.  Smell is one of the senses that disappears in the aging process and older people often lose interest in most foods, except sweets, because the food becomes bland to them without smell.  Smell is an important first indicator of some dangers as it can detect more remote sensation than taste. To taste something it must touch the tongue but smells waft through the air to your nose.    

The system for smell develops between 16 and 24 weeks of gestation and is in place and ready to function by about 24 weeks gestation. The first taste buds appear at 8-9 weeks gestation with most being present by about 16 weeks gestation. Some refinement continues but most full term babies have a fully developed taste system at birth.

The system of smell is perhaps the strongest sense in infants and babies are able to recognize the smell of their mother’s breast milk from that of another person (the study was done using breast pads) almost from birth. They also respond to strong smells with avoidant movements from an early age. I would avoid strong perfumes and air fresheners around very young infants as these might be unpleasant to their sensitive system. In a study (titled “Natural odour preferences of newborn infants change over time.” by [My paper]H Varendi, R H Porter, J Winberg) it was shown that babies preferred their mother’s unwashed natural breast over the washed and soapy smelling other breast during the first week to 10 days of life.  It has been proposed that smell is the first sense used in socializing as newborns begin to recognize different people by their smell, which allows them to respond socially to those they know and those they do not know from a very early age.

These systems rely on experience after birth to become completely developed. The brain records tastes and smells so that a child can recognize what they mean. Infants can register likes and dislikes from the start. Due to their limited experience, infants are happy with relatively bland food and do not need salt or sugar added to foods to want them. However, they recognize variations in their food and may reject food that tastes

“funny”. Many breast feeding mothers report that their baby is not interested in the breast after they have eaten a certain type of food. Which foods trigger that response are different for each baby but all are strong flavored foods. In my case, it was pickled foods that I had to avoid. This is learned by the baby through experience with foods and by the mother in watching her baby’s reaction to feeding.

On the other hand, older people who have lost some of their sense of smell are best able to taste the flavors that are tasted by the tongue. Sweet is the strongest, being at the front of the tongue, followed by salt. Older adults will often only express interest in sweet foods and will often over salt foods in order to experience variation in tastes. Many older adults will say that food these days doesn’t taste like it used to. For them, it is probably true.

It is thought that these two systems have some protective functions as most really bad smells and bitter tastes are not good for people so your own body can offer some protection against certain poisons. However the system is not foolproof and some unpleasant tasting things are not harmful while some harmful things are not unpleasant. It has been noted that during pregnancy, many women are exceptionally sensitive to smells, which may be a primitive form of guiding them towards the particular foods they need.

In any case, the sense of smell is one of the least studies and most underrated the special senses. Below are some links to references on the sense of smell:

http://www.wonderbabiesco.org/UserFiles/File/Browne%20chemosensory%2008.pdf

http://www.kidandparent.in/childdevelopment/baby-development-smell

http://www.jstor.org/discover/10.2307/1130478?uid=3738128&uid=2&uid=4&sid=21102562218157

http://serendip.brynmawr.edu/exchange/node/518

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.