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Your sense of touch incorporates your
skin, which is your body’s largest
organ; your central nervous system,
which includes your brain, spinal cord
and neurons; and 5million sensory
nerve receptors. Even a simple action
such as picking up amug of hot cocoa
is actually a complex process!
The process begins in your skin, where
stimulated sensors send electrical pulses
to neurons. These electrical pulses are
passed from neuron to neuron until
they reach the spinal cord.Your spinal
cord carries the signal to your brain,
which translates the signal and tells
your body how to respond. For
example, if themug is too hot,
youwill quickly remove
your hand.
There are two categories
of receptors: rapidly
adapting and slowly
adapting. Rapidly
adapting receptors
respond to change
in a stimulus quickly
(such as your reaction to
amug of hot cocoa), but
they can’t sense the dura-
tion of a stimulus touching
the skin. Slowly adapting
receptors are good at sensing
continuous pressure, but not
at sensingwhen a stimulus
started or ended. Slowly
adapting receptors are at
work as youmaintain your
gripon amug of cocoa
that is not too hot.
Receptors can perceive pressure,
temperature, pain and location.
Mechanoreceptors perceive sensa-
tions including pressure, vibration and
texture. Themost sensitive of these are
found in the top layers of the skin (the
epidermis), themiddle layer (the
dermis) and the non-hairy sections
of the skin, including the palms, lips,
tongue, soles of feet, fingertips, eyelids
and face. Deeper under the skin, along
the joints, tendons andmuscles, are
mechanoreceptors that can feel vibra-
tions. These promote physical activities.
Thermoreceptors, found in the dermis
around the face and ears, perceive sen-
sations related to temperature.We have
both cold and hot receptors. Cold recep-
tors begin picking up sensationswhen
the temperature of your skin falls below
95 degrees F. They lose stimulation
below 41 degrees, such aswhen your
hands go numb after being in the cold
for a long time. Hot
receptors pick up
when your
rises above
86 degrees;
after 113
degrees, pain
receptors take
over. Think
about the receptors
that areworkingwhen
you pick up that hot
mug of cocoa.
Themore than 3million pain
receptors in your body pick up
all kinds of pain. These impor-
tant receptors trigger feelings
of sharp pain so that you can
quickly respond to a burn,
cut or other danger. Pain re-
ceptors also create dull pains
to remind you to protect parts of
your body that are healing from
an injury. If you’ve ever pulled or
strained amuscle during a sport,
it’s your pain
receptors that are telling you
to take a few days off from
the activity to heal.
Proprioceptors sense the position of
different parts of the body in relation to
each other and the environment. They
are located in your tendons,muscles
and joints. The proprioceptors
determine how onemovement relates
to others. For example, if you’re doing
yoga and stretch your legmuscle too
far, proprioceptors kick in to cause the
muscle to contract and shorten,
protecting you from injury.
What youneed:
Three tall glasses of water, one filledwith
verywarmor hot water (not burning), one
filledwith room-temperaturewater andone
filledwith icewater; a clock to time yourself
1. Grab the glass of hot waterwithonehand,making sure that
your palm is touching the glass. Grab the glass of icewaterwith
your other hand, holding the glass in a similar fashion.
2. Hold the hot and cold glasses for 60 seconds, and then grab
the room-temperature glasswithbothhands, palms touching
the glass. Does it feel hot or cold?
Your brain received confusingmessages from your hands
about the temperatureof the third glass. Thehandoriginally
holding thehot glass told you the third glasswas cold, whereas
thehandoriginally holding the cold glass told you the third
glasswas hot. But theywereboth touching the same glass.
How can this be?
Your skindoes not perceive the exact temperature of an
object. Instead, it senses thedifference in temperatureof anew
object in comparison to the temperatureof anobject the skin
was already used to (“relative temperature”). This iswhy enter-
ing a body of water, such as a pool or lake, can seem cold at
first. Your bodywas used to thewarmer air, but it adjusted to
the temperatureof thewater after being in it for awhile.
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