Download Tactile and Body Senses

Tactile sense
Touch is one of the five senses (the others being smell, taste, vision, and hearing) through which animals
and people interpret the world around them. While the other senses are localized primarily in a single
area (such as vision in the eyes or taste in the tongue), the sensation of touch (or contact with the outside
world) can be experienced anywhere on the body, from the top of the head to the tip of the toe. Touch is
based on nerve receptors in the skin which send electrical messages through the central nervous system
to the cerebral cortex in the brain, which interprets these electrical codes. For the most part, the touch
receptors specialize in experiencing either hot, cold, pain, or pressure. Arguably, touch is the most
important of all the senses; without it animals would not be able to recognize pain (such as scalding
water), which would greatly decrease their chances for survival. Research has also shown that touch has
tremendous psychological ramifications in areas like child development, persuasion, healing, and
reducing anxiety and tension.
How we feel the outside world
Our sense of touch is based primarily in the outer layer of skin called the epidermis. Nerve endings that
lie in or just below the epidermis cells respond to various outside stimuli, which are categorized into
four basic stimuli: pressure, pain, hot, and cold. Animals experience one or a combination of these
sensations through a complex neural network that sends electrical impulses through the spinal cord to
the cerebral cortex in the brain. The cerebral cortex, in turn, contains brain cells (neurons) arranged in
columns that specialize in interpreting specific types of stimuli on certain parts of the body.
Scientists have identified several types of touch receptors. Free nerve ending receptors, located
throughout the body at the bases of hair, are associated primarily with light pressure (such as wind) and
pain. Meissner corpuscles are nerve endings contained in tiny capsules and are found primarily in the
fingertips and areas especially sensitive to touch (in the form of low-frequency vibrations), like the soles
of the feet and the tongue. The Pacinian corpuscles look like the cross section of an onion and are found
in deep tissues in the joints, the genitals, and the mammary glands. They are extremely sensitive to
pressure and are also stimulated by rapid movement of the tissues and vibrating sensations. Ruffini
endings, which are also located in the deeper layers of the skin, respond to continuous stimulation, like
steady pressure or tension within the skin. Merkel disks, are found near the base of the epidermis and
also respond to continuous stimulation or pressure. The skin also contains specific thermoreceptors for
sensing hot and cold and nociceptors that identify high intensity stimulation in the form of pain.
Most, if not all of these receptors, are designed to adapt or become accustomed to the specific
stimulation they interpret. In other words, the receptor does not continue to register a constant ‘‘feeling’’
with the same intensity as when it first begins and may even shut off the tactile experience. Imagine, for
example, putting on a wool sweater over bare skin. The initial prickly sensation eventually abates,
allowing the wearer to become accustomed to the feeling. Other examples include wearing jewelry such
as rings, necklaces, and watches.
These receptors are also found in greater numbers on different parts of
the body. For example, peoples’ backs are the least sensitive to touch,
while their lips, tongue, and fingertips are most sensitive to tactile
activity. Most receptors for cold are found on the surface of the face
while thermoreceptors for warmth usually lie deeper in the skin and are
fewer in number. A light breeze on the arm or head is felt because
there tend to be more sense receptors at the base of the hairs than
anywhere else.
Touch and health
Touch has a tremendous impact on most animals’ physical and
psychological well being. Numerous studies of humans and other animals have shown that touch greatly
impacts how we develop physically and respond to the world mentally. For example, premature babies
that receive regular massages will gain weight more rapidly and develop faster mentally than those who
do not receive the same attention. When baby rats are separated from their mothers for only 45 minutes,
they undergo physiological or biochemical changes, specifically a reduction in a growth hormone.
Touching of premature babies can also stimulate growth hormones (such as the hormone needed to
absorb food) that occur naturally in healthy babies.
A baby does not have to be premature or sickly to benefit from touch. Even healthy babies show benefits
from touch in terms of emotional stability. Difficult children often have a history of abuse and neglect.
The reason is that touch serves as a type of reassurance to infants that they are loved and safe, which
translates into emotional well being. In general, babies who are held and touched more tend to develop
better alertness and cognitive abilities over the long run.
Touch continues to have a great psychological impact throughout peoples’ lives. Even adults who are
hospitalized or sick at home seem to have less anxiety and tension headaches when they are regularly
touched or caressed by caretakers or loved ones. Numerous studies have shown that touch also has a
healing power. Researchers have found that touch reduces rapid heart beats and irregular heart beats
(arrhythmias). Another study showed that baby rats who are touched often during infancy develop more
receptors to control the production of biochemicals called glucocorticoids, which are known as stress
chemicals because of their ability to cause muscle shrinkage, high blood pressure, elevated cholesterol,
and more.
Touch’s psychological impact goes beyond physical and mental health. Researchers have shown that
touch is a powerful persuasive force. For example, studies have shown that touch can have a big impact
in marketing and sales. Salespeople often use touch to establish a camaraderie and friendship that can
result in better sales. In general, people are more likely to respond positively to a request if it is
accompanied by a slight touch on the arm or hand. In a study of waiters and waitresses, for example,
those that lightly touched a patron often received better tips.
Kinesthetic sense
The ability to know accurately the positions and movements of one's skeletal joints.
Kinesthesis refers to sensory input that occurs within the body. Postural and movement information are
communicated via sensory systems by tension and compression of muscles in the body. Even when the
body remains stationary, thekinesthetic sense can monitor its position. Humans possess three specialized
types of neurons responsive to touch and stretching that help keep track of body movement and position.
The first class, called Pacinian corpuscles, lies in the deep subcutaneous fatty tissue and responds to
pressure. The second class of neurons surrounds the internal organs, and the third class is associated
with muscles, tendons, and joints. These neurons work in concert with one another and with cortical
neurons as the body moves.
The ability to assess the weight of an object is another function of kinesthesia. When an individual picks
up an object, the tension in his/her muscles generates signals that are used to adjust posture. This sense
does not operate in isolation from other senses. For example, the size-weight illusion results in a
mismatch between how heavy an object looks and how heavy the muscles "think" it should be. In
general, larger objects are judged as being heavier than smaller objects of the same weight.
The kinesthetic sense does not mediate equilibrium, or sense of balance. Balance involves different
sensory pathways and originates in large part within the inner ear.
Vestibular sense
One of two proprioceptive sensory systems that provide us with input about the positions of our own
bodies.
The equilibrium sense, generally associated with balance, provides feedback about the positions and
movements of our heads and bodies in space. The other system—the kinesthetic sense—tells us about
the orientation of different parts of our bodies in relation to each other. While the kinesthetic
information needed by the brain comes from joints and muscle fibers throughout the body, the receptors
for equilibrium are located in the semicircular canals and vestibular sacs of the inner ear. (The
equilibrium sense is also called the vestibular sense, and the relevant parts of the inner ear are sometimes
called the vestibular system or apparatus).
The semicircular canals are three pretzel-like curved tubes arranged at angles roughly perpendicular to
each other, with the two vestibular sacs located at their base. Both the canals and sacs contain fluid and
tiny hair cells, which act as receptors. When a person's head moves, the fluid disturbs the hair cells,
which stimulate a branch of the auditory nerve, signaling the brain to make adjustments in the eyes and
body. A movement at any given angle will have its primary effect on one of the three canals.
Overstimulation from extreme movements will produce dizziness and nausea. Our sense of body
position when we are at rest is provided by the vestibular sacs, which contain small crystals called
otoliths (literally, "ear stones") that exert pressure on the hair cells. In their normal position, the otoliths
inform our brains that we are standing or sitting upright. When the head is tilted, the position of the
otoliths changes, and the signal sent to the brain changes accordingly. The neural connections of
the vestibular system lead to the cerebellum, the eye muscles, and a part of the autonomic nervous
system involved in digestion (which accounts for the link between dizziness and nausea).
Sensing PAIN
Pain is a ____________________ signal! Everyone experiences pain differently because of __________
___________________________________________________________________________________.
There are many theories as to how pain works. Two of the most well known are the Gate Control
Theory and the Biopsychosocial Theory (see your chart). The Gate Control Theory claimes that there is
a “_________________________________” in the ________________________ that controls which
pain signals are and are not sent to the brain based on the number of large v. small fibers that are active.
The more small fibers that are active, the more pain you will feel.
How to manage pain is a controversial issue as well. Some people believe in using pharmacology
(medicine) and surgery, which others take a more alternative approach and recommend acupuncture,
hypnosis, and yoga.
http://www.ted.com/talks/elliot_krane_the_mystery_of_chronic_pain.html
Name _________________________________________ Period __________