The Eight Sensory Systems

January 25, 2019
As we discussed in early December, sensory is a hot button word right now.  We all have a sensory system, and it is responsible for understanding and navigating the world around you.  As children we learn about the five senses:  sight, sound, taste, touch, and smell.  The sensory systems responsible for these are vision, auditory, oral, tactile, and olfactory.  We also have three other sensory systems that collect sensory information from the environment to help our bodies properly function: vestibular recognizes movement, proprioception recognizes where the body is in space, and interoception recognizes the needs within our body.

As a parent, caregiver, or medical professional you may have seen ideas for sensory play or sensory bins.  Every minute of every day our bodies are collecting information, bringing it into our body, delivering it to the appropriate areas of the brain, interpreting it, and then making an appropriate response. These sensory systems have a big job and if they are blocked or inhibited,  daily activities can become difficult.

Sensory Processing, also called sensory integration, is the brain’s ability to organize the information coming from all of the systems and to use it appropriately.  This information allows appropriate responses to guide motor, behavior, and emotional responses.  When the system is intact this process happens automatically, unconsciously, and nearly instantaneously.

An example is when you pick up a cup of water off the table you automatically adjust the amount of force you need to pick it up and move it to where you anticipate.  If you walk into a darker room you will pause and allow your eyes to adjust, and you may look for landmarks in the room or feel for the light switch to turn on the light.

As we talked about earlier, we have eight sensory systems. When occupational therapists talk about sensory processing or sensory integration they are normally referring to the eight sensory systems. Most people have heard of the classic five senses  and easily identify if their child or the child they are around responds excessively or does not respond at all to one of these senses.  Often people outside of the medical field do not realize there are three other less recognizable sensory systems that play a powerful role in our body’s ability to organize and participate in all daily activities.

Here are the eight sensory systems you’ll typically hear OT talk about:

  • Vestibular: This system recognizes movement and is important in relation to balance and motion.  The area responsible for recognizing this sense is located in the middle ear and is composed of three canals filled with fluid that move depending on the position you are in. This system is activated when you move your head but also by the force of gravity and shifts in the environment. This system is very complex; it is what can lead some people to spin without ever becoming dizzy and others to be easily motion sick.  It is one of the three systems that acts in the very basic parts of the brain including the brain stem to organize and calm the pathways.  It can calm a child or arouse a child depending on how it is delivered.
  • Proprioception: This system gets input from the muscles tendons and joints all over your body and gives a sense of body awareness. When we push, pull or engage our muscles, receptors allow our body  to collect information on how they are moving and know where they are and how to continue or support a movement. Proprioception helps us know what force to use when interacting with an object such as a door or cabinet or a pencil.  It allows us to plan our next move and do things like climb the monkey bars or jump where we mean too.  Proprioception is another major calming and organizing force in the brain and allows us to interact with activities in our environment.
  • Tactile: This system is responsible for recognizing our sense of touch, located in sensory receptors in our skin and mouth. This system has two important jobs.  It needs to tell us when our body has touched something or been touch and what it is that we have touched.  It is essential because it allows us to recognize when touch is safe like clothing and not safe like the hot stove. This system also allows us to feel and discriminate between light touch and deep touch and know how to react to them. Light touch tends to be alerting and deep touch is the third system that can create calm and organization in the brain.
  • Visual: The visual system deals with the sense of vision, what we see and how our brain interprets it.  Visual acuity is part of it but it also includes how we are able to understand what we are seeing.  Visual perceptual skills of figure ground, visual closure, position in space, and form constancy are affected by the visual system. (see our previous post on visual perception for more details).
  • Auditory: The auditory system deals with hearing.  Similar to the visual system hearing deals with more than just being able to hear sounds accurately.  It also deals with being able to determine if the sound is important or it can be tuned out.  Another function of the system is to identify where the sound is coming from and what it could mean.  This system helps identity the person’s safety and can easily trigger a fight or flight response.
  • Olfactory: This system is responsible for the sense of smell, it also influences sense of taste, and is the only sense that is directly tied to the part of the brain responsible for emotional memories.
  • Gustatory: This system is responsible for sense of taste.  This system identifies different flavors and textures that come in the mouth.  It is another system that also acts as a safety mechanism for the body and can cause a fight or flight reaction to flavors or textures it tastes.
  • Interoception:  This system is responsible for the understanding of the internal condition of our body, or the feeling of what is going on inside your body. The recognition of emotions, nausea, hunger, headaches, or digestion are all aspects of interoception.

These systems work together to collect information for the brain and help the body know how to react throughout the day.  When these systems are working with normal thresholds they are coordinated and allow us to function without realizing work is being done.  When they are not coordinating because some systems under respond and some over respond, then everyday activities can become more difficult and sensory processing disorder and sensory dysfunction are the culprits.  The good news is that Occupational Therapy can often identify and devise treatment plans to address these sensory system breakdowns.

 

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