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: Objective Evidence for the Anatomical
Unity of Nerve Cells, arguing that the nervous system is comprised of neurons. Twenty-one years
later, scientists using the electron microscope show Ramón y Cajal’s arguments are correct.
1944 Oswald Avery, Colin Macleod, and Maelyn McCarty discovered that DNA (Deoxyribonucleic
Acid) was the material of which genes are made.
1953 James Watson and Francis Crick discovered the double helix structure of DNA.
1957 The Russian satellite Sputnik was launched.
1960–
1980
The Leakeys, Louis and Mary, and their sons Richard, Jonathon, and Philip discovered the
fossilized remains of prehumans and the earliest humans near Lake Turkana in Kenya.
1978 Louise Brown, the world’s first “test-tube baby” is born in England.
SUGGESTIONS FOR FURTHER READINGS
Adelman, G. (Ed.). (1987). Encyclopedia of Neuroscience. (Vols. 1 & 2). Boston: Birkauser. Provides brief essays on a
wide range of topics by leading neuroscientists.
Bloom, F. F., & Lazerson, A. (1988). Brain, Mind, and Behavior. (2nd ed.). New York: Freeman. Built around the PBS
eight-part television series, “The Brain.” Includes excellent color illustrations.
Carlson, N. R. (1998). Physiology of Behavior (6th ed.). Boston: Allyn and Bacon.
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PSYCHOLOGY AND LIFE
Damasio, A. R. (1994). Descartes’ Error. Emotion, Reason, and the Human Brain. New York: Putnam.
Edwards, A. J. (1994). When Memory Fails: Helping the Alzheimer’s and Dementia Patient. New York: Plenum Press.
Offers an excellent overview of the disease processes involved in these illnesses and of how to care for both the
patient and the caregiver in easily comprehensible terms.
Gazzaniga, M. S. (1998). The Mind’s Past. Berkeley, CA: University of California Press.
Helfer, M. E., & Kempe, R. S. (1997). The Battered Child. (5th ed.). Chicago: University of Chicago Press.
Plomin, R., & McClearn, G. E. (Eds.). (1993). Nature—Nurture and Psychology. Hyattsville, MD: APA Press. Leading
environmentalists and geneticists explore the gap between nature and nurture and contend that the concept may
indeed be linked.
Sacks, O. W. (1985). The Man Who Mistook His Wife for a Hat and Other Clinical Tales. New York: Harper & Row.
Offers fascinating accounts of work with individuals with various neurological and neuropsychological
problems.
Sacks, O. W. (1995). An Anthropologist on Mars: Seven Paradoxical Tales. New York: Knopf
Sapolsky, R. M. (1994). Why Zebras Don’t Get Ulcers: A Guide to Stress, Stress Related Diseases, and Coping. New
York: Freeman.
Sapolsky, R. M. (1997). The Trouble with Testosterone: And Other Essays on the Biology of the Human Predicament.
New York: Scribner.
DISCOVERING PSYCHOLOGY
PROGRAM 3: THE BEHAVING BRAIN
Overview
The structure and composition of the brain: how neurons function, how information is collected and transmitted,
and how chemical reactions determine every thought, feeling, and action.
Key Issues
The biology of the brain, how the brain processes information, the electroencephalogram (EEG), neurometric
evaluation, the effects of drugs on the functions of the brain, the brain’s own manufactured chemicals, and
neurotransplantation.
Demonstrations
Multiple brain wave recording to reveal various types of brain malfunction.
Effects of chemicals on learning and memory in rats.
New Interviews
John Gabrieli illustrates how the brain stores and retrieves information.
PROGRAM 4: THE RESPONSIVE BRAIN
Overview
How the brain controls behavior and, conversely, how behavior and environment influence the brain’s structure
and functioning.
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CHAPTER3: THE BIOLOGICAL BASES OF BEHAVIOR
Key Issues
The effect of human touch on the growth of premature babies, the effect of the mother’s touch on the growth of
rats, psychosocial dwarfism, the effect of stress on memory and learning in rats, how behavior modifies the
physiology of the African Cichlid fish, and the effects of social status on the health of baboons
Archival Demonstrations
Effects of change in social status on sexual reactions and growth of fish.
Effects of social status on hormones and behavior in wild baboons.
Demonstrations
Effects of physical stimulation on growth of brain, body and health of rats.
Relationship between early stimulation and adult resistance to stress-induced decline in memory of
rats.
Interviews
Tiffany Field explains the benefits of touch on the cognitive and motor development of premature babies.
Saul Shanberg underscores the importance of contact by the mother in the process of growth and development
in rats.
Michael Meaney examines the effects of stress on memory and learning in rats.
R. Fernald examines the effects of behavior on the physiology of the brain and the effects of the brain on
behavior in African Cichlid fish.
Robert Salopsky discusses the direct effects of social status on the health of wild baboons.
FILMS AND VIDEOS
The Brain (1993). Encyclopedia Britannica Educational Co., 50 minutes
This program describes the structure and function of the brain. Using a variety of video techniques, the
viewer is shown the major anatomical structures of the brain, and the function of each of these is discussed.
The Brain, Mind, and Behavior Series (1984). IU (FI), 60 minutes
A PBS series that examines the mysteries and intricacies of the human brain. Because the role of the brain is
the focus of each program, any of these can be a helpful supplement to your coverage of brain structure and
function. An excellent series.
Program 1: The Enlightened Machine
A general introduction to the brain’s functions. Uses models, graphics, animation, and real-life action. Examines
the mysteries of consciousness.
Program 2: Vision and Movement
Explains how people perceive the world and how the brain coordinates vision and movement. Includes
appearances by champion diver Greg Louganis and Nobel Prize winners Hubel and Weisel.
Program 3: Rhythms and Drives
Uses examples from both the animal world and human society to explain instinctive, unconscious rhythms and
drives, and the working of the primitive portion of the human brain. Shows the behavioral changes that result
from injury to the hypothalamus and shows the effects of seasonal and circadian rhythms on some people.
Program 4: Stress and Emotion
Explains the interrelationship of pain, anxiety, behavior, and the brain. Uses two case studies, one about a man
who suffered an accidental frontal lobotomy, the other about a stress-ridden professional, to tell the story.
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PSYCHOLOGY AND LIFE
Program 5: Learning and Memory
Discusses how humans remember, and why they forget. Focuses on brain organization, activity at the synapse,
and workings of the hippocampus to explain memory.
Program 6: The Two Brains
Explores the cortical hemispheres, the relation of thought and language, and sex differences of the human brain.
Illustrates lateral specialization through the research conducted with split-brain patients.
Program 7: Madness
Explores the lives of schizophrenics and their families to explain how much brain researchers know and what they
have yet to accomplish to understand schizophrenia fully.
Program 8: States of Mind
Surveys the current state of our knowledge about the brain and what lies in the future. Examines how this
knowledge will be applied in the coming years to the fields of medicine and artificial intelligence.
Decision (1985). IU (FFHS), 27 minutes
Demonstrates how the brain organizes input and output to make simple but life-saving decisions. Explains
how the cortex assesses incoming information, sends outgoing messages to the muscles, and stores maps of
the world and the body. Shows how circuits of nerve cells operate in the brain and how individual nerve
cells function.
Odyssey: Lucy and the First Family (1980). PBS, 59 minutes
The study of 3.5 million-year-old Lucy, one of the most complete human skeletons that has been discovered,
has led to a controversy regarding evolution. This videotape provided a link between the field of
anthropology and the social sciences.
Our Talented Brain (1985). IU (FFHS), 27 minutes
Explores the physiological brain capacity of human beings, their use of memory, and their use of symbols.
Explains how these capacities relate to the neural structure of the brain.
The Infinite Voyage: Fires of the Mind (1988). WQED and the National Academy of Sciences, 58 minutes
Covers the development of human intelligence, and how cells, electric signals, and chemicals make up the
creative mind of man. Features a study of the cells of Einstein’s brain.
The Nervous System: Nerves at Work (1982). Salubris Productions (PBS), 26 minutes
The electrochemical nature of neural transmission and neural action in reflexive behaviors is examined in
this film.
CASE STUDY LECTURE LAUNCHER
Five-and-a-half weeks before her twins were due, Christine felt the first sharp pains of labor. Her husband
drove her to the hospital where, for 16 hours, the two of them followed the breathing instructions given to
them during their natural childbirth class. Then a fetal monitor showed that the heartbeat of one of the
babies was weakening. Doctors quickly performed a Cesarean section. Within minutes, 4-pound Nicole and
3-pound 14-ounce Alexis entered the world.
Immediately after birth, Nicole and Alexis joined half a dozen other babies in the Neonatal Intensive Care
Unit. For two-and-a-half weeks, electronic devices monitored their vital signs. Experienced nurses tended to
their physical needs and held them frequently. Christine spent a good part of each day with her babies,
holding and rocking them and feeding them her breast milk from bottles, awaiting the day when she could
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CHAPTER3: THE BIOLOGICAL BASES OF BEHAVIOR
actually breast feed them. Wearing diapers barely the size of cocktail napkins, the twins looked fragile and
unfinished. With no layers of baby fat, every little rib showed.
Had Nicole and Alexis been born 20 years earlier, their first few weeks of life would have been quite
different. Until the late 1970s, premature infants were touched as little as possible. Parents and medical
personnel feared that any unnecessary contact with the outside world might harm the babies. Fortunately
for Nicole and Alexis, we now know better.
Research with infant rats and humans has led scientists to conclude that brain functioning can be altered
by touch, and that, for newborns, touch is essential for normal growth and development. Biologist Saul
Schanberg found that when rat pups were removed from their mothers, the levels of an enzyme important
for growth decreased dramatically. The longer they were deprived of maternal contact, the less responsive
the pups became. The effects of maternal deprivation could be reversed in only two ways: by returning them
to their mother, who immediately started to lick them, or by having a researcher vigorously stroke them with
a small paintbrush. Shanberg concluded that, “the need for a mother’s touch is really brain based. It is not
just nice to have it. It’s a requirement for the normal development and growth of the baby.”
Psychologist Tiffany Field, who had collaborated with Schanberg, conducted similar stimulation studies of
premature human infants. Her research team randomly selected 20 preemies to receive periodic massages
throughout the day, while 20 others received normal hospital treatment in the intensive care unit, treatment
that did not include massage. According to Field, “The premature babies who were massaged for 45
minutes a day for ten days before they were discharged gained 47 percent more weight than the babies who
did not get massaged. They were more active. They were more alert.” Eight months later, the massaged
babies had maintained their weight advantage and were more advanced in motor, cognitive, and emotional
development. This research is being extended and replicated in larger samples of preemies in order to
establish the power of human touch on biological and psychological health.
In the United States, more than 0.25 million infants are born prematurely each year. Those who are touched
and cuddled leave the hospital several days sooner than usual, reducing care costs by about $3,000 per
child. Unfortunately, not all hospitals apply what scientists have learned about the positive effects of early
touch on development. If they did, the lives of thousands of children would be improved, saving billions of
dollars each year—both practical benefits of this basic research.
When Nicole and Alexis left the hospital, they were still small, but were developing so well that doctors felt
confident they would be all right. At home, the babies shared a crib in the living room, where relatives and
friends who remarked on their tiny size were encouraged to pick up the babies gently and cuddle them.
Christine and her husband were acutely aware of the important role played by human touch in the optimal
development of the brain and the mental and psychical processes that it controls.
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CHAPTER 4
Sensation
LEARNING OBJECTIVES
On completion of this chapter, students should be able to:
1. Understand the basic processes through which sensory stimuli are converted into neural
events
2. Describe Müller’s doctrine of specific nerve energies
3. Relate the differences in thresholds (absolute and difference) and know why these concepts
are relevant
4. Discuss the concepts of response bias and signal detection theory
5. Identify the parts and functions of the human visual system
6. Understand the basic processes involved in color vision, and the theories supporting those
processes
7. Describe the physiological components of the auditory system
8. Explain the two theories of pitch perception
9. Define pheromones and describe their role in olfaction
CHAPTER OUTLINE
I. Sensory Knowledge of the World
A. Sensation is the process by which stimulation of sensory receptors produces neural
impulses that represent experiences inside or outside the body
B. This chapter deals with sensory processes, with the sense organs and peripheral aspects of
the nervous system that put you in contact with the world around you
C. Your senses have two basic functions
1. Survival
2. Sensuality
D. While some animals specialize in one sensory medium, such as the sight of hawks, humans
are equipped with a variety of sensory mechanisms
E. Psychophysics
1. The study of the relationship between physical stimuli and the
behavior or mental experiences the stimuli evoke. The oldest field in
psychology.
2. Gustav Fechner (1801–1887)
a) The most significant figure in psychophysics
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b) Coined the term “psychophysics” and developed procedures to
relate the intensity of physical stimulus to the magnitude of the
sensory experience.
3. Absolute Thresholds and Sensory Adaptation
a) The absolute threshold for stimulation is the smallest, weakest
stimulus energy that the organism can detect
b) Operationally defined as the stimulus level at which a sensory
input is detected half of the time
c) Sensory Adaptation is the diminishing responsiveness of sensory
systems to prolonged stimulus input. Sensory systems are more
sensitive to change in stimulus input than to steady input.
4. Response Bias
a) The systematic tendency for an observer to favor responding in a
particular way that is unrelated to the qualities of the sensory
stimulus. For instance, tending to say “yes” or “no” all of the time.
There are at least three sources of response bias.
i) Desire
ii) Expectation
iii) Habit
5. Signal Detection Theory
a) A systematic approach to the problem of response bias
b) Focuses on the process of making a judgment about the presence
or absence of a stimulus
c) Unlike classical psychophysics which conceptualized a single
absolute threshold, Signal Detection Theory identifies two distinct
processes in sensory detection: Sensory Processes and Decision
Processes
i) Sensory Processes reflect an observer’s sensitivity to the
stimulus
ii) Decision Processes reflect an observer’s response bias to
the stimulus
6. Difference Thresholds
a) The difference threshold for stimulation is the smallest physical
difference between two stimuli that can still be recognized as a
difference
b) Operationally defined as the point at which the stimuli are
recognized as different half of the time
c) The difference threshold value is known as the Just Noticeable
Difference (JND)
7. Weber’s Law
a) The JND between stimuli is a constant fraction of the intensity of
the standard stimulus
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F. From Physical Events to Mental Events
1. Sensory Physiology
a) The study of the way biological mechanisms convert physical
events into neural events
b) Transduction is the conversion of one form of energy, such as
light, into another form, such as nerve impulses
2. The Doctrine of Specific Nerve Energies
a) Proposed by Johannes Müller in 1826
b) Different sensory experiences, such as sight and smell, do not
produce different types of nerve activity. Rather they produce the
same type of nerve activity, but in different regions of the brain.
c) All sensory systems share the same basic flow of information.
Environmental events are detected by specialized sensory receptor
neurons, called stimulus detector units, which convert the
physical energy received from the environment into neural signals
that can be processed by the central nervous system.
II. The Visual System
A. The Importance of Vision
1. The most complex, highly developed, and important sense for humans
and most other mobile creatures
2. Provides a tremendous evolutionary advantage
B. The Human Eye
1. Light enters the eye through the cornea, a transparent bulge on the front
of the eye
2. Light then passes through the anterior chamber, which is filled with a
clear liquid called aqueous humor
3. Then through the pupil, an opening in the opaque iris
4. Then through the lens, which focuses the incoming light
5. Then through the vitreous humor, another clear liquid
6. And then finally strikes the retina, a thin sheet of neuron that lines the
rear wall of the eyeball
C. The Pupil and the Lens
1. The iris makes the pupil dilate to control the amount of light entering the
eye. The lens focuses the light on the retina, reversing and inverting the
light as it does so. The lens is responsible for focusing to account for the
distance to the object.
2. Accommodation is the change in the thickness of the lens. Problems with
accommodation are responsible for many vision problems, such as near-
and far-sightedness.
D. The Retina
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1. The retina is composed of specialized photoreceptor cells called rods and
cones that convert light energy into nerve energy
a) Rods function best in low light
b) Cones function best in bright light
2. Dark adaptation is the gradual improvement of the eyes’ sensitivity after
a shift in illumination from light to near darkness
3. The area of sharpest vision is called the fovea, a small area near the
center of the retina that contains only densely packed cones
4. Bipolar cells are nerve cells that combine information from many receptor
cells and send the results to ganglion cells
5. Ganglion cells then integrate the information from bipolar cells into a
single firing rate
6. The axons of the ganglion cells comprise the optic nerve, which carries
visual information to the brain
7. Horizontal and Amacrine cells do not send information to the brain but
rather integrate information across the retina
a) Horizontal cells connect receptors to each other
b) Amacrine cells connect bipolar cells to bipolar cells and ganglion
cells to ganglion cells
8. The optic disk or blind spot is the area where the optic nerve exits the
retina. It contains no receptor cells. Blindness is not experienced at this
spot because the blind spots for each eye are different areas of the visual
field and because the brain automatically fills in the blind spot.
E. Pathways to the Brain
1. After processing by other brain regions, the ultimate destination of much
visual information is the part of the occipital lobe known as the visual
cortex
2. The axons of the millions of ganglion cells that form the optic nerve
come together at the optic chiasma, where they are divided into two
bundles called optic tracts
3. Half of the nerve fibers from each retina stay on the side from which they
originated. The other half cross over to the other side of the brain.
4. Much visual information then flows to the primary visual cortex, where
roughly 30 anatomical subdivisions of the primary visual cortex process
information concerning form, color, position, and depth
F. Seeing Color
1. Visible light (wave length of 400–700 manometers) is just a small portion
of the electromagnetic spectrum, which includes X rays, microwaves, and
radio waves
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PSYCHOLOGY AND LIFE
2. Wavelength refers to the distance between crests of two consecutive
waves. Wavelength determines the color perceived.
3. All experiences of color can be described in terms of hue, saturation, and
brightness
a) Hue captures the qualitative experience of color of the light
stimulus
b) Saturation captures the purity and vividness of color sensations
c) Brightness captures the intensity of the light
4. Humans can discriminate about 7 million different colors
5. The combination of all wavelengths of light yields white light
6. Wavelengths of light that appear directly across from each other on the
color wheel are called complementary, and create the sensation of white
light when mixed
7. Color Blindness is the inability to distinguish colors. More males than
females are color blind, and most color blindness involves the inability
to distinguish red from green.
8. There are two primary theories of color vision: The Young-Helmholtz
Trichromatic Theory and the Opponent-Process Theory
a) The Trichromatic Theory of color perception, proposed by Sir
Thomas Young and Hermann von Helmholtz, suggests that all
colors perceived are produced by just three types of color receptors
in the eye: red, green, and blue. All other colors are combinations
of these. This theory adequately explains color blindness and
people’s color sensations, but did not explain afterimages and
certain types of color blindness.
b) The Opponent-Process Theory of color perception, proposed by
Ewald Hering, suggests that color results from three systems, each
of which includes two opponent elements: red versus green, blue
versus yellow, or black versus white. Hering argued that
afterimages were produced when one element of a system became
fatigued, due to over stimulation, and thus led to the over
contribution of its opponent element. This theory also better
explained why color blindness is usually found in pairs.
9. After debating the relative merits of these two theories, scientists came to
agree that they are not in conflict, but rather describe different stages in
color perception
10. A modern version of the Opponent-Process Theory, proposed by
Hurvich and Jameson, suggests that the two members of each color pair
work in opposition by means of neural inhibition. Some ganglion cells
are excited by light that appears red and inhibited by light that appears
green. Other cells are excited by green light and inhibited by red light.
G. Complex Visual Analysis
1. David Hubel and Torsten Wiesel won a Nobel Prize for their work on
receptive fields in the visual cortex in 1981
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2. Hubel and Wiesel found there are several types of receptive cells
a) Simple cells respond most strongly to bars of light in their
“favorite” orientation
b) Complex cells respond most strongly to moving bars of light in
their “favorite” orientation
c) Hypercomplex cells respond most strongly to moving bars of light of
a particular length or angle
III. Hearing
A. Hearing is the Principle Sensory Modality for Human Communication
B. The Physics of Sound
1. Sound travels as a vibrational sine wave through a medium, usually air,
at a rate of about 1100 feet per second
2. Sine waves have two basic properties: frequency and amplitude
a) Frequency measures the number of cycles the wave completes in a
given amount of time and is usually measured in Hertz (Hz), or
cycles per second
b) Amplitude measures strength of the wave in peak to valley height
C. Psychological Dimensions of Sound
1. Pitch is the highness or lowness of a sound as determined by a wave’s
frequency. High frequencies produce high pitch, while low frequencies
produce low pitch.
2. Loudness is the physical intensity of a sound as determined by a wave’s
amplitude. Small amplitude waves are experienced as quiet sound and
large amplitude waves are experienced as loud sound.
3. Timbre reflects the complex components of a sound wave. A pure tone
has only one frequency and one amplitude. Most sounds, however, are
not pure tones, which is reflected in timbre.
D. The Physiology of Hearing
1. In order for hearing to occur, four basic energy transformations must
take place
a) First, airborne sound waves must be translated into fluid waves
within the cochlea of the ear. Sound waves travel into the ear until
they reach the end of the canal. There they encounter the tympanic
membrane or eardrum. The sound waves move the eardrum, and
the eardrum transmits the vibrations from the outer ear to the
middle ear, which contains the hammer, the anvil, and the stirrup.
These tiny bones transmit the vibrations from the eardrum to the
primary organ of hearing, the cochlea in the inner ear.
b) Second, the fluid waves must stimulate mechanical vibrations of
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PSYCHOLOGY AND LIFE
the basilar membrane. Vibration of fluid in the cochlea causes a
coiled tube membrane in the cochlea, the basilar membrane, to
move in a wavelike fashion.
c) Third, these vibrations must be converted into electrical impulses.
The wavelike motion of the basilar membrane bends tiny hair cells
connected to the membrane. As the hair cells bend, they stimulate
nerve endings, transforming the wave motion into neural activity.
d) Fourth, the impulses must travel to the auditory cortex from the
cochlea via the auditory nerve. Information from one ear goes to
both sides of the brain.
2. There are two types of hearing impairment, each caused by a defect in
one or more components of the auditory system: conduction deafness
and nerve deafness
a) Conduction deafness is the less serious of the two and involves a-
problem in the conduction of air vibrations to the cochlea. It can
often be corrected by the insertion of artificial anvils or stirrups.
b) Nerve deafness is more serious and involves a defect in the neural
mechanisms that create nerve impulses or that relay them to the
auditory cortex
E. Theories of Pitch Perception
1. Two major theories have been posited to explain sensations of pitch:
place theory and frequency theory
a) Place theory, proposed first by Helmholtz and later modified by
Bekesy, suggests that different portions of the basilar membrane
move depending on the frequency of the sound wave. High-
frequency tones produce greatest motion at the base of the cochlea,
while low-frequency tones produce the greatest motion at the
opposite end.
b) Frequency theory suggests that the rate of vibration of the tone is
reflected in the rate of vibration of the basilar membrane. If a tone
vibrates at 100 Hz, the basilar membrane will also vibrate at 100
Hz and will cause neurons to fire at 100 Hz. For high-pitched
sounds, however, this is impossible, because they cannot fire more
than 1,000 times per second. The volley principle may overcome
this limitation.
2. The Volley Principle suggests that several neurons could work together
and could fire in a volley to match higher cycles per second
3. Frequency and Place Theories are not mutually exclusive. Place theory
accounts well for pitch perception of frequencies above 1,000 Hz, while
frequency theory accounts well for pitch perception of frequencies below
5,000 Hz.
F. Sound Localization
1. Some animals, such as bats, use echolocation instead of vision to
determine distances, locations, sizes, textures, and movements of objects.
Humans lack this ability, but do use sound to determine location
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through two primary mechanisms, assessment of relative timing and
relative intensity.
2. Relative timing involves the comparison of the relative times at which
incoming sound reaches the ear. For example, a sound to your right
reaches your right ear before it reaches your left ear.
3. Relative intensity involves the comparison of the relative intensity at
which incoming sound reaches the ear. The head casts a sound shadow
over the ear farthest from the sound that weakens the sound.
IV. Your Other Senses
A. Smell
1. Odors first interact with receptor proteins on the membranes of tiny
hairs (olfactory cilia) in your nose
2. As few as eight molecules of a substance can initiate a nerve impulse,
but at least 40 nerve endings must be stimulated before a substance can
be smelled.
3. Once initiated, nerve impulses convey odor information to the olfactory
bulb, located just above the receptors and just below the frontal lobes of
the cerebrum
4. Olfactory neurons, unlike most neurons, are constantly dying and being
replaced
5. Although it is thought that smell developed primarily as a means of
detecting food, it can also be used for active communication by the
secretion of pheromones
6. Pheromones are chemical substances used by a specific species to signal
sexual arousal, danger, territorial boundaries, and food sources
B. Taste
1. Many tastes are really smells, as the two work closely together when we
eat
2. The surface of the tongue is covered with papillae
3. Many papillae contain clusters of taste receptor cells called taste buds
4. Taste buds respond best to one of four primary taste qualities: sweet,
sour, bitter, and saline
5. Taste buds may be damaged by alcohol, smoke, and acids, but the taste
system is the most resistant to damage of all sensory systems, as taste
receptors are replaced every few days, even more often than smell
receptors
C. Touch and Skin Senses
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PSYCHOLOGY AND LIFE
1. Cutaneous senses are sensations produced by the skin, such as pressure,
cold, and warmth. Because the skin responds to so many types of
stimuli, many different types of receptors are located near the surface of
the skin.
2. Meissner corpuscles respond best when something rubs against the skin
3. Merkel disks are most active when a small object exerts steady pressure
on the skin
4. The skin has separate receptors for hot and cold
5. Erogenous zones are areas of the skin that give rise to erotic, sexual
sensations
D. The Vestibular and Kinesthetic Senses
1. Vestibular sense tells how the body is oriented in the world with respect to
gravity through tiny hairs in fluid-filled sacs and canals in the inner ear
a) The saccule and utricle detect acceleration and deceleration
b) The semicircular canals are at right angles to each other and can
thus detect movement in any direction
c) Motion sickness occurs when information from the visual system
conflicts with information from the vestibular system
2. The kinesthetic sense provides constant sensory feedback about what the
body is doing during motor activities. There are two sources of
kinesthetic information: receptors in the joints and receptors in muscles
and tendons
a) Receptors in the joints respond to pressures that accompany
different positions of the limbs and to pressure changes that
accompany movements
b) Receptors in the muscles and tendons respond to changes in
tension that accompany muscle shortening and lengthening
E. Pain
1. Pain is the body’s response to noxious stimuli that are intense enough to
cause damage or threaten to do so. Pain is critical to survival. People
with insensitivity to pain often become scarred and their limbs deformed
from injuries that could have been prevented had they been sensitive to
pain.
2. Pain mechanisms
a) Nociceptive pain is the negative feeling induced by a noxious
external stimulus, such as a hot stove
b) Neuropathic pain is caused by the abnormal functioning or over
activity of nerves
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CHAPTER 4: SENSATION
c) The network of pain receptors is a fine mesh that covers the entire
body. Some receptors respond only to temperature, while others
respond to chemical or mechanical stimuli.
d) Peripheral nerve fibers transmit signals to the central nervous
system in two ways:
i) Fast-conducting, myelinated nerves
ii) Slower, smaller, nonmyelinated nerves
e) Pain impulses start at the spinal cord, are relayed to the thalamus,
and then to the cerebral cortex
3. The Psychology of Pain
a) Emotional responses, context factors, and subjective interpretation
can be as important as actual physical stimuli in determining how
much pain is experienced
b) Phantom limb phenomenon is the experience of sensation or pain
in a limb that is no longer there. It occurs in up to 10 percent of
amputees.
c) Pain is partly a psychological response and, thus, can be
influenced by psychological processes, such as hypnosis, deep
relaxation, and thought distraction. The Lamaze preparation for
childbirth is an excellent example of the psychological control of
pain.
d) The Gate-Control Theory of pain, proposed by Ronald Melzack,
suggests that cells in the spinal cord act as neurological gates,
interrupting and blocking some pain signals and letting others
through to the brain. The brain and receptors in the skin send
messages to the spinal cord to open or close the gates.
e) In recent years Melzack proposed an updated neuromatrix theory
of pain which incorporates the reality that people often experience
pain with little or no physical cause.
DISCUSSION QUESTIONS
1. What other senses might there be that humans lack?
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