Download Sense of Touch and Feeling

Trisha Brenneman
LE: 2010, Research Paper
December 3, 2013
Sense of Touch and Feeling
We as humans are blessed with five amazing senses; touch, smell, hearing, tasting and
sight. But, out of all five I’d have to say I find the miracle of touch to be the most intriguing. The
first thing that comes to mind when the topic of touch and feeling arise is the skin. There are
about four to five million sensory nerve receptors in your skin and that is just the beginning.
What would the world be like without this helpful addition? This topic is something to explore
when asking what it means to simply have the sensation of touch. Another important thing to
mention is the reality that we have found ways to supplement missing limbs, yet not how to
substitute feeling. Until recently this was the truth, but science is on its way to make that all in
the past. Overall without feeling life would be completely different and seem lacking of the
things most of us take for granted. It’s the beautiful addition we all should all try to understand
just a little bit more.
The skin is the largest organ in the
body, weighing about six pounds by
average in an adult. It is nearly twice the
weight of the brain or liver. There are
four layers to the skin: the epidermis,
basement membrane zone, dermis and
the subcutaneous layer. The skin is
continually renewing itself throughout the entire span of a human’s lifetime. There are many
functions that the skin holds; it is a physical barrier, helps regulate body temperature through
sweating; prevents harmful microorganisms and chemicals from entering the body, induced
synthesis of vitamin D, prevention of excessive water loss or absorption, ability to repair itself
after injury, and contains specialized nerve cells responsible for the sense of touch. Skin itself is
the first line of defense for humans, it keeps us safe and helps us maintain the rest of our bodily
functions.
“Touch is the first of the five senses to develop in the womb and thereon plays an
essential role in our everyday life and even to our own very existence. Through the sense of
touch we can detect different textures and temperatures of different levels. Our skin allows us
to detect if something is squishy, wet slimy, smooth, rough, hard, soft, fluffy, spiky, ridged, hot
or cold and even by how much in relations to our body temperature. Our skin containing
sensory receptors also allows us to identify several distinct types of sensations (stimuli) such as
tapping, vibration, pressure, pain, heat, and cold.” (Edmondson) Because our skin enables us to
do so we are able to protect ourselves when we receive this information. Pain is a warning
signal that tells us something is not right. The protective measures of our skin keep us going
without too much harm from the outside world.
Even though the basics of our skin alone would make anyone react in awe, the reality is
that the sensation of touch receptors is something to really be amazed with. We are able to
feel the heat radiate of the sun and the air blow over our face. The sensation of kissing and
hugging from a loved one is all because of touch. The most sensitive tactile receptors are on our
back of the neck, the face, lip, tongue, upper arm, fingers, chest, soles of feet and between the
legs. The world, how things look, their shape and size are all projected to us through the sense
of touch. (Edmondson)
The skin receives a stimulus to a sensory receptor, it then sends the “message” as an
electrical signal. The impulse travels by the sensory neuron from the peripheral nervous system
to the spinal cord then brain, also known collectively as the central nervous system. Once the
message is analyzed by the brain, it then registers to the effect of the stimulus and reacts. If the
stimulus is innocent, the brain would respond as so. Sometimes this would be by laughing,
smiling, focused, etc. The interpretation of sensations in each life is molded by preceding
experiences. This can be applied to both internal and external conditions.
More incredible is the fact that if a stimulus is dangerous or painful, not only would the
prior pathway be taken but, a quicker response would occur as well. This happens in the spinal
cord before it is sent to the brain to be analyzed. It is called the reflex arc. This offers a way for
instantaneous
response from the
dangerous stimuli. It
is an unconscious
reflex action that
occurs before the
signal has extended to
the brain. The
reaction that ensues
only in the spinal cord is extremely imperative to prevent severe harms by stimuli.
The brain follows through with a message that is sent through the spinal cord and then
picked up by the motor neurons to the muscles and glands. Contractions of muscles to pull
away from stimuli occurs here. If the stimulus is not harmful and perhaps the brain finds the
sensation to be enjoyable or comforting, then the message may tell the muscles in your face to
relax and/or increase your heart rate, release of a specific gland, etc. The stimulus determines
how our brains tell the body to react, both positive and negative the message must get to our
brain for us to us to consciously react to what has happened. (Edmondson)
Touch does not only occur from external stimulus. We also have internal stimulus that
tell us what is going on in our organs and just as important how to function in our daily lives.
Proprioception is when one is aware of body and position of limbs within one’s own body, it is
required in order to move at all. This is an internal form of tactile sense. Our bodies’ first sense
to develop in embryos is the sense of touch. Infants are able to learn about their immediate
environment and bond with others through the sense of touch. Touch is constant, it never
shuts off. Even in old age this sense thrives longer. The most fascinating part about touch is that
without it, infants will fail to thrive. Touch is necessary for healthy development in all
individuals. (Leonard) Touch is defined as “the special sense by which contact with the body of
an organism is perceived in the conscious mind”. (Gardner)
The way the body signals sensations of touch is much more complex than one single
pathway or receptors on the skin. When the sensory neuron sends a signal it moves to the
thalamus and multiple parts of the cerebral cortex. We all have similar arrangements of sensory
neurons and where they go, this is what determines how we evaluate the signal. The
interesting part is that each individual’s somatotopic map is different and determined by that
persons own experience in life. This is in result determines how each person may react
differently to the same stimulus. Psychologist and doctors have determined that affectionate
touch must happen in order for a child to develop physically, mentally, and emotionally. There
has been many studies showing strong relation with lack of affection to illness, depression,
violence and memory deficits. (Leonard) The reality is without touch babies wouldn’t survive
the first years.
For those who have lost a limb and along with the physical use for it goes the ability to
feel the people and world around them. Our first answer was prosthetic limbs, this gave us the
ability to walk without legs and grab items without hands. But yet, something was still missing.
The miracle of feeling the world around us seemed impossible to recreate. Prosthetic limbs
over time were able to move and become much more useful. In the past years scientist have
been able to make supersensitive artificial skin. Just in this past year they began looking at
touch in three specific aspects: location, pressure and timing. They tested these out on a
primate named Rhesus macaques. He was trained to tell the difference between indentions or
pokes of the hand. They poked two fingers and depending where the second poke occurred in
relation to the first is where the primate was trained to look. Next, they would physically wpoke
one finger and electrically stimulate neurons associated with a different finger. They found that
macaques responded to the second poke as if it was physical.
Next phase in this research they probed the primates ability to tell the difference
between pressure on the hand. They found the poking with different forces lead to greater
number of neurons becoming activated. So in order to mimic greater pressure there should be
an increase in neurons stimulated. After all the testing, the scientists where able to create an
algorithm that specifies how much current was needed to make the sensation specific to
pressure. Once again the primate reacted to various electrical stimulations as if he was really
poked by different pressures. The final step was putting a prosthetic hand with various
pressures and converting the indentations to electrical stimulations. As expected, the primate
responded as if his own hands were being poked. In result they were successful in relating
pokes to the hand directly to the specific electrical stimuli that tells the brain it is feeling a
perceived pressure.
This study was monumental in progressing toward prosthetic limbs that have sensory
capabilities. This is just the beginning, there is still tremendous amounts of work to be done.
Another important test will be to actually transplant this work to a human subject. If this works
spinal cord injuries and amputees could be helped. The possibility is out there we just need to
go forward and make this work to help those who would benefit so greatly. (BenningtonCastro)
I see the future expanding right before our eyes. As a generation who has witnessed so
much change in the evolution of AI, I am hopeful this is just the beginning. With everything we
know we can change the lives of so many of those not so lucky. It is exciting and nerve racking;
mind boggling and fascinating; scary and welcoming; really the ideas that stem from AI are one
big paradox. I love that something so complicated and confusing, can at the same time make so
much sense. I am on the fence about a lot of the things we are creating. However, I do believe
the more we learn, the more we can improve life. This will make it more possible than ever to
do good for our human race. It is so exciting knowing I will be here to witness all the milestones
we have yet to surpass.
We as humans are capable of five senses to use in the world around us. Touch is by far
one we are just now understanding. Skin is the amazing organ that gets the ball rolling for this
specific sense. Take this organ away and one cannot even imagine a world without it. Without
the sensation of touch humans would not survive. The ones that are not so lucky and lose
sensation or even a whole limb have not been promised to feel again, but that is all changing.
The more we learn about our sense of feeling, the more we can change this grave future and
give hope back to those who have had it taken away. The more we learn about touch and
feeling the more we can understand this beautiful gift our senses have given.
Bibliography
Bennington-Castro, J. (2013). A Major Breakthrough in Bringing the Sense of Touch to
Prosthetic Limbs
http://io9.com/a-major-breakthrough-in-bringing-the-sense-of-touch-to-1445039422
Edmondson, R. (2006). The Skin: Sense of Touch- How we feel things around us.
http://www.myuniversalfacts.com/2006/06/skin-sense-of-touch-how-we-feel-things.html
Gardner, E. P. (2001) Encyclopedia of Life Sciences. New York, NY. John Wiley and Sons
Leonard, C. (2009). The Sense of Touch and How It Affects Development.
http://serendip.brynmawr.edu/exchange/node/4356