Sensing Body Position

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Chapter 3 Sensation and Perception
know, for example, that successful placebo treatments for human pain appear to operate by activating the endorphin system.
■ What evidence would help to evaluate the alternatives?
More placebo-controlled studies of acupuncture are needed, but it is difficult to control
for the placebo effect in acupuncture treatment, especially in double-blind fashion (e.g.,
Kaptchuk, 2001). (How could a therapist not know whether the treatment being given
was acupuncture or not? And from the patient’s perspective, what placebo treatment
could look and feel like having a needle inserted and twirled in the skin?) Nevertheless,
researchers have tried to separate the psychological and physical effects of acupuncture—
for example, by using blunted or phony needles, mock electrical nerve stimulation (in
which electrodes are attached to the skin but no electrical stimulation is given), or stimulation at other sites on the skin (Kaptchuk et al., 2006; Park, White, & Ernst, 2001).
Researchers must also learn more about what factors govern whether acupuncture
will activate the endorphin system. Other important unknowns include the types of
pain for which acupuncture is most effective, the types of patients who respond best,
and the precise procedures that are most effective. Knowing more about the general
relationship between internal painkilling systems and external methods for stimulating
them would also be valuable.
■ What conclusions are most reasonable?
Although acupuncture is not a cure-all, there seems to be little doubt that, in some circumstances, it does relieve pain and reduce nausea (British Medical Association, 2000;
National Institutes of Health Consensus Conference, 1998). One study, for example, found
that acupuncture before surgery reduced postoperative pain and nausea, decreased the need
for pain-relieving drugs, and reduced patients’ stress responses (Kotani et al., 2001). Another
found electrical-stimulation acupuncture to be more effective than either drugs or mock
stimulation at reducing nausea following major breast surgery; the acupuncture group also
reported the least postoperative pain (Gan et al., 2004). So although some critics argue that
further expenditures for acupuncture research are not warranted, further studies will probably continue. The quality of their methodology and the nature of their results will determine whether acupuncture finds a more prominent place in Western medicine.
Sensing Body Position
Most sensory systems receive information from the external world, such as the light
reflected from a flower or the feeling of cool water. But as far as the brain is concerned,
the rest of the body is “out there,” too. You know about the position of your body and
what each of its parts is doing only because sensory systems provide this information
to your brain. These sensory systems are described as proprioceptive (meaning
“received from one’s own,” pronounced “pro-pree-oh-SEP-tiv”).
proprioceptive Referring to sensory
systems that tell us about the location
of our body parts and what each is
doing.
kinesthesia The proprioceptive sense
that tells us where the parts of the
body are with respect to one another.
Kinesthesia In the biology and behavior chapter, we describe the case of Christina,
a woman who did not recognize her own body. She had lost her sense of kinesthesia
(pronounced “kin-es-THEE-see-uh”), which tells us where the parts of the body are in
relation to one another. To better appreciate kinesthesia, try this: Close your eyes; then
hold your arms out in front of you and touch your two index fingers
learn together. You probably did this easily because your kinesthetic sense told you
by
doing where each finger was with respect to your body. You depend on kinesthetic
information to guide all your movements, from walking to complex athletic actions such
as running down a basketball court while dribbling a ball and avoiding an opposing
player. These movement patterns become simple and fluid because, with practice, the
brain uses kinesthetic information automatically. Normally, kinesthetic information
comes primarily from the joints and muscles. Receptors in muscle fibers send information to the brain about the stretching of muscles. When the position of the bones
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in review
Sensing Your Body
BODY SENSES
Sense
Energy
Conversion of Physical
Energy to Nerve Activity
Pathways and
Characteristics
Touch
Mechanical deformation of
skin
Skin receptors (may be stimulated by hair on the skin)
Nerve endings respond to changes
in weight (intensity) and location
of touch.
Temperature
Heat
Sensory neurons in the skin
Changes in temperature are
detected by warm-sensing and
cool-sensing fibers. Temperature
interacts with touch.
Pain
Increases with intensity of
touch or temperature
Free nerve endings in or near
the skin surface
Changes in intensity cause the
release of chemicals detected by
receptors in pain neurons. Some
fibers convey sharp pain; others
convey dull aches and burning
sensations.
Kinesthesia
Mechanical energy of joint
and muscle movement
Receptors in muscle fibers
Information from muscle fibers is
sent to the spinal cord, thalamus,
cerebellum, and cortex.
?
1. Gate control theory offers an explanation of why we sometimes do not feel
.
2. Professional dancers look at the same spot as long as possible during repeated spins. They are trying to avoid the dizziness
caused when the
sense is overstimulated.
3. Without your sense of
, you would not be able to swallow food without choking.
changes, receptors in the joints set off neural activity. This coded information goes to
the spinal cord and then to the thalamus, along with sensory information from the
skin. Finally it goes to the cerebellum and to the somatosensory cortex, both of which
help coordinate movements (see Figures 2.8, 2.9, and 2.10).
Balance Have you ever been on a roller coaster? How did you feel when the ride ended?
The vestibular sense (pronounced “ves-TIB-u-ler”) tells the brain about the position
vestibular sense The proprioceptive
sense that provides information about
the position of the head and its
movements.
of the head (and therefore the body) in space and about its general movements. You have
probably heard it referred to as the sense of balance. People usually become aware of the
vestibular sense only when they overstimulate it and become dizzy or motion sick.
The inner ear contains the organs for the vestibular sense. Each ear has two vestibular sacs filled with fluid and containing small crystals called otoliths (“ear stones”) that
rest on hair endings. Three arc-shaped tubes, called the semicircular canals, are also fluid
filled (see Figure 3.14). Tiny hairs extend into the fluid in the canals. When your head
moves, the otoliths shift in the vestibular sacs and the fluid moves in the semicircular
canals, stimulating hair endings. This process activates neurons that travel along the
auditory nerve, signaling the brain about the amount and direction of head movement.
Neural connections from the vestibular system to the cerebellum help coordinate
bodily movements. Connections to the part of the autonomic nervous system that
affects the digestive system help create the nausea that may follow overstimulation of
the vestibular system—by a roller coaster ride, for instance. Finally, connections to the
eye muscles produce vestibular-ocular reflexes, which cause your eyes to move opposite
to your head movements. These reflexes allow you to focus on one spot even when your
head is moving. You can experience these reflexes by having a friend spin you around
on a stool for a while. When you stop, try to fix your gaze on one point in
learn the room. You’ll be unable to do so, because the excitation of the vestibular
by
doing system will cause your eyes to move repeatedly in the direction opposite
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