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Biology and Behavior
Neurons
The nervous system has two parts. The central nervous system consists of
the brain and spinal cord. The peripheral nervous system is made up of
nerve cells that send messages between the central nervous system and other
parts of the body. Nerve cells are called neurons.
Components of a Neuron
• The cell body produces energy
that fuels the neuron’s activity.
• Dendrites receive information
from other neurons and pass
the message through the cell
body.
• An axon transmits information
away from the cell body.
Components of a Neuron
(con’t)
• Myelin is a white, fatty
substance that covers the axon,
insulating and protecting it. The
myelin sheath helps to speed
up the work of neurons.
• Axon terminals branch out at
the end of the axon.
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Biology and Behavior
The Communication Process
• Messages are sent from the axon terminals of one neuron to the
dendrites of another neuron.
• In order for this process to happen, the message must cross a
synapse.
• A synapse is a junction between the axon terminals of one neuron
and the dendrites of another.
• Messages travel in only one direction. Messages
– enter the dendrites
– travel through the cell body and axon to the axon terminals
– cross the synapses to the dendrites of other neurons
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Biology and Behavior
Original Content Copyright by HOLT McDougal. Additions and changes to the original content are the responsibility of the instructor.
Biology and Behavior
Neurotransmitters: The Body’s Chemical
Messengers
• Neurons send messages across synapses through the release of
neurotransmitters.
• Neurotransmitters are chemicals that are stored in sacs in the axon
terminals.
• A neuron fires, or sends a message, by releasing neurotransmitters.
– The message is converted into an electrical impulse that travels through
the neuron.
– The message is transmitted to the next neuron by other
neurotransmitters until the message arrives at its destination.
• There are several kinds of neurotransmitters.
– Acetylcholine is involved in the control of muscles and in learning and
memory.
– Dopamine is involved primarily in motor behavior.
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Biology and Behavior
Original Content Copyright by HOLT McDougal. Additions and changes to the original content are the responsibility of the instructor.
Biology and Behavior
The Central Nervous System
• The central nervous systems consists of the neurons of the spinal
cord and the brain.
• The spinal cord is a column of nerves about as thick as a thumb that
extends from the brain down the back.
• The spinal cord transmits messages between the brain and the
muscles and glands in the body.
• The spinal cord sends messages to specific muscles.
• The spinal cord is involved in spinal reflexes.
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Biology and Behavior
The Peripheral Nervous System
The Somatic Nervous
System
The Autonomic Nervous
System
• The somatic nervous system
transmits sensory messages to the
central nervous system.
• The autonomic nervous system
regulates the body’s vital functions,
such as heartbeat, breathing,
digestion, and blood pressure.
• It carries messages from the
voluntary muscles and sense
organs.
• It is activated by touch, pain,
changes in temperature, and
changes in body position.
• It has two divisions.
• The sympathetic nervous system
reacts to stress.
• The parasympathetic nervous
system restores peace to the
body’s systems
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Biology and Behavior
Early Beliefs About the Brain
• In ancient times, people did not attribute human psychological
processes such as thinking to the working of the brain.
• Instead, people widely believed that the body was inhabited by souls
or demons.
• Ancient Egyptians believed that a little person dwelled within the skull
and regulated behavior.
• The Greek philosopher Aristotle thought that the soul resided in the
heart.
• Today we recognize that the mind, or consciousness, dwells within
the brain.
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Biology and Behavior
Parts of the Brain
The Hindbrain
• The medulla is involved in heart rate, blood pressure, and breathing.
• The pons regulates body movement, attention, sleep, and alertness.
• The cerebellum is involved in balance and coordination.
The Midbrain
• Areas within the midbrain are involved in vision and hearing.
• Contains part of the reticular activating system, which is important
for attention, sleep, arousal, and alertness.
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Biology and Behavior
The Forebrain
• The thalamus serves a relay station for sensory stimulation.
• The hypothalamus is vital to the regulation of body temperature, the
storage of nutrients, and various aspects of motivation and emotion.
It is also involved in hunger, thirst, sexual behavior, caring for
offspring, and aggression.
• The limbic system is involved in learning and memory, emotion,
hunger, sex, and aggression.
• The cerebrum makes up about 70 percent of the brain’s weight and
is where most conscious and intellectual activities take place.
• The cerebral cortex is the outer layer of the brain. It is the part that
thinks, and it also deals with memory, language, emotions, complex
motor skills, perception, and more.
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Biology and Behavior
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Biology and Behavior
The Cerebral Cortex
• The cerebral cortex has a left side and right side.
• Each side is called a hemisphere.
• The corpus callosum is the structure that connects the two
hemispheres.
• Information received by one side of the body is transmitted to the
opposite hemisphere of the brain.
• Each hemisphere is divided into four parts:
– frontal lobe
– parietal lobe
– temporal lobe
– occipital lobe
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Biology and Behavior
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Biology and Behavior
Senses and Motor
Behavior
Association Areas
•
The association areas of the
cerebral cortex shape information
into something meaningful.
• The temporal lobe is the hearing, or
auditory, area of the cerebral
cortex.
•
The association areas in the
frontal lobes function as the
brain’s executive center.
• Messages received from the skin’s
sensory receptors are projected to
the sensory cortex in the parietal
lobe.
•
Association areas provide the core
of the working memory.
•
The frontal region of the brain thus
retrieves visual, auditory, and
other kinds of memories.
•
Other association areas make
possible the psychological
functions of language.
• The occipital lobe is the primary
visual area of the cerebral cortex.
• These sensations include warmth,
cold, touch, and pain.
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Biology and Behavior
Language Abilities
• For nearly all right-handed people,
language functions are based in the
left hemisphere.
• Language functions are also based
in the left hemisphere of about two
out of three left-handed people.
• Wernicke’s area connects sounds
and sights. When this area is
damaged, people find it difficult to
understand speech.
• Broca’s area is involved in speech.
When this area is damaged, people
speak slowly and use simple
sentences.
Left and Right
Hemispheres
•
The left hemisphere is usually
more involved in logic, problem
solving, and mathematical
computation.
•
The right hemisphere is more
concerned with imagination, art,
feelings, and spatial relations.
•
Split-brain operations have taught
psychologists much of what they
know about left- and righthemisphere functioning.
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Biology and Behavior
Methods of Studying the Brain
Accidents
Lesions
• Researchers are able to learn how
the brain is related to psychological
functions through the study of brain
damage due to accidents.
• Scientists can study a brain by
cutting, removing, or destroying
parts of it.
Electrical Stimulation
Electroencephalogram
• Electrical stimulation of the brain
has shown that specific areas are
associated with specific types of
sensations.
• The EEG is a device that records
electrical activity of the brain.
• It is not a reliable research tool.
• This method is used on laboratory
animals.
• EEG readings can help diagnose
certain psychological disorders and
to help locate tumors.
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Biology and Behavior
Brain Imaging
• Brain imaging can provide information about
– brain damage
– cancers
– difficult surgeries
• Brain imaging techniques include
– CAT scans
– MRI scans
– PET scans
– fMRI scans
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Biology and Behavior
Three Endocrine Glands
• The endocrine system consists of glands that secrete substances
called hormones.
The Pituitary Gland
The Thyroid Gland
• It lies just below the hypothalamus
in the middle of the brain.
• It produces the hormone thyroxin.
• It secretes hormones that include
human growth hormone, prolactin,
and oxytocin.
• Some pituitary hormones stimulate
other endocrine glands such as the
adrenals, thyroid, and ovaries or
testes.
• Thyroxin affects the body’s
metabolism.
• Too little thyroxin can cause
hypothyroidism and cretinism.
• Too much thyroxin can cause
hyperthyroidism.
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Biology and Behavior
The Adrenal Glands
• They are located above the kidneys.
• The outer layer, or cortex, secretes cortical steroids.
• Cortical steroids increase resistance to stress, promote muscle
development, and make the liver release stored sugar to provide
energy during emergencies.
• The adrenal glands produce adrenaline and noradrenaline.
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Biology and Behavior
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Biology and Behavior
Ovaries and Testes
Ovaries in females and testes in males produce hormones that
influence sexual development and functions.
Both glands produce estrogen, progesterone, and testosterone.
Estrogen and Progesterone
Testosterone
• Estrogen and progesterone are
female sex hormones that regulate
the menstrual cycle.
• Testosterone is the primary male
sex hormone.
• Estrogen has psychological as well
as biological effects.
• Low levels of estrogen and
progesterone are found in males.
• It aids the growth of muscle and
bone.
• It aids development of primary and
secondary sex characteristics.
• Small amounts are found in
females.
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Biology and Behavior
Heredity, Genes, and Chromosomes
• Heredity is the transmission of characteristics from parents to
offspring.
• Psychologists study heredity to understand people’s behavior.
• Genes are the building blocks of heredity.
• Genes are found in threadlike structures called chromosomes.
– Genes are composed of DNA.
– Most normal human cells have 46 pairs of chromosomes divided into 23
pairs.
– In each pair, one chromosome is from the father and one is from the
mother.
– The twenty-third pair determines gender.
– When a child is born without all 46 chromosomes, physical and
behavioral disorders may result.
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Biology and Behavior
Original Content Copyright by HOLT McDougal. Additions and changes to the original content are the responsibility of the instructor.
Biology and Behavior
Nature and Nurture
• The debate over the role of biology in determining who we are as
people is called the “nature-nurture” issue.
• Nature refers to what people inherit.
• Nurture refers to environmental factors.
• “Nature” supporters argue that biological makeup primarily
determines people’s traits and personalities.
• “Nurture” supporters argue that the environment and everyday
experiences determine how we behave and think.
• Both views are extreme.
• Most psychologists think that both nature and nurture determine
psychological traits.
• The role of heredity is still a controversial topic.
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Biology and Behavior
Kinship Studies
• Kinship studies focus on the roles that heredity and environment play
in determining a trait.
• Kinships refers to the degree to which people are related.
• Twin Studies Studies of identical and fraternal twins provide a way
to learn about relative influence of nature and nurture.
• Adoptee Studies Psychologists also study children who have been
adopted to look for relative similarities between children and their
adoptive and biological families.
• Twins Reared Apart One of the most useful types of kinship studies
focuses on twins who have been reared apart.
– Lack of common experiences makes it more likely that similarities are
attributable to genetic factors.
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Biology and Behavior
Current Research in Psychology
The Genographic Project
Have you ever wondered where your ancestors came from? Some families can
trace their history back several centuries. But where were your ancestors 1,000
or 10,000 years ago? A remarkable program called the Genographic Project
aims to map the migratory history of all humankind. What can it tell us about
what we have inherited from our ancestors?
• The Genographic Project analyzes
DNA voluntarily contributed by
people around the world.
• The project aims to find out how
people migrated and populated the
world.
• Another goal is to learn why people
look so different from each other.
• The ultimate goal of the project is to
uncover a web of migration stories
that will explain how humans
populated the world and to show
how closely the human family is
related.
• The project relies on DNA
contributions from hundreds of
thousands of people.
Original Content Copyright by HOLT McDougal. Additions and changes to the original content are the responsibility of the instructor.
Biology and Behavior
Original Content Copyright by HOLT McDougal. Additions and changes to the original content are the responsibility of the instructor.
Biology and Behavior
Original Content Copyright by HOLT McDougal. Additions and changes to the original content are the responsibility of the instructor.