This document provides an overview of the biology of behavior and the nervous system. It discusses neurons and how they communicate via neurotransmitters and action potentials. It describes the structure and functions of the central nervous system including the brainstem, thalamus, limbic system, and cerebral cortex. It also covers the endocrine system and tools used to study brain activity like EEG, MRI, fMRI, and PET scans. Key topics include neural communication at synapses, the roles of different neurotransmitters, lateralization of brain functions, and brain plasticity.

1. The Biology
of Behavior
Chapter 2

2. Searching for
the biology of
“self”
2
Is our identity in the
heart?
In the brain?
In the whole body?
Biological
Psychologists
explore the
associations
between body,
mind, and behavior.

3. Overview: What We Have in Mind
 Building blocks of mind: Neurons and how they
communicate (neurotransmitters)
 Systems that build the mind: Functions of Parts of
the Nervous system
 Supporting player: the slower-communicating
Endocrine system (hormones)
 Tools for examining the brain and its activities
 More primitive and advanced brain structures

4. Neural and Hormonal Systems

5. Neurons and Neuronal Communication:
The Structure of a Neuron
There are billions of neurons
(nerve cells) throughout the body.

6. Action potential:
a neural impulse that travels down an
axon like a wave
Just as “the wave” can flow to
the right in a stadium even
though the people only move
up and down, a wave moves
down an axon although it is
only made up of ion exchanges
moving in and out.

7. The
neuron
receives
signals
from other
neurons;
some are
telling it to
fire and
some are
telling it
not to fire.
• When the
threshold is
reached, the
action potential
starts moving.
• Like a gun, it
either fires or it
doesn’t; more
stimulation does
nothing.
• This is known as
the “all-or-
none” response.
The
action
potential
travels
down the
axon
from the
cell body
to the
terminal
branches
.
The signal is
transmitted to
another cell.
However, the
message must
find a way to
cross a gap
between cells.
This gap is
also called the
synapse.
How neurons communicate
(with each other):
When does the cell send the action
potential? When it reaches a threshold.
The threshold is reached when
excitatory (“Fire!”) signals
outweigh the inhibitory (“Don’t
fire!”) signals by a certain amount.

8. The synapse is
also known as the
“synaptic
junction” or
“synaptic gap.”
The Synapse
The synapse is a
junction between the
axon tip of the
sending neuron and
the dendrite or cell
body of the receiving
neuron.

9. Neurotransmitters
Neurotransmitters are
chemicals used to send
a signal across the
synaptic gap.

10. Reuptake:
Recycling Neurotransmitters [NTs]
Reuptake:
After the neurotransmitters
stimulate the receptors on
the receiving neuron, the
chemicals are taken back
up into the sending neuron
to be used again.

11. Seeing all the Steps Together
Neural Communication:

12. Some Neurotransmitters and Their Functions
Neurotransmitter Function Problems Caused by Imbalances
Roles of Different Neurotransmitters
Serotonin Affects mood, hunger,
sleep, and arousal
Undersupply linked to depression;
some antidepressant drugs raise
serotonin levels
Dopamine
Influences movement,
learning, attention, and
emotion
Oversupply linked to schizophrenia;
undersupply linked to tremors and
decreased mobility in Parkinson’s
disease and ADHD
Acetylcholine
(ACh)
Enables muscle action,
learning, and memory
ACh-producing neurons deteriorate as
Alzheimer’s disease progresses
Norepinephrine Helps control alertness
and arousal
Undersupply can depress mood and
cause ADHD-like attention problems
GABA gamma-
aminobutyric acid
A major inhibitory
neurotransmitter
Undersupply linked to seizures,
tremors, and insomnia
Glutamate
A major excitatory
neurotransmitter;
involved in memory
Oversupply can overstimulate the brain,
producing migraines or seizures; this is
why some people avoid MSG
(monosodium glutamate) in food

13. Serotonin
pathways
Networks of neurons that
communicate with serotonin
help regulate mood.
Networks of neurons that
communicate with dopamine are
involved in focusing attention
and controlling movement.
Dopamine
pathways

14. Divisions of the Nervous System

15. The Inner and Outer Parts of the
Nervous System
The Central
Nervous
System (CNS),
the brain and
spinal cord, is
the body’s
decisionmaker.
The Peripheral
Nervous
System (CNS),
gathers
information
from the body
and sends CNS
decisions out to
the body.

16. Types of Neurons
Sensory
neurons carry
messages IN
from the body’s
tissues and
sensory
receptors to the
CNS for
processing.
Motor
neurons carry
instructions
OUT from the
CNS out to the
body’s tissues.
Interneurons
(in the brain
and spinal cord)
process
information
between the
sensory input
and motor
output.

17. The Peripheral Nervous System

18. The
Autonomic
Nervous
System:
The sympathetic
NS arouses
(fight-or-flight)
The
parasympathetic
NS calms
(rest and digest)

19. Neural Networks
These complex webs of interconnected neurons form with
experience.
Remember: “Neurons that fire together, wire together.”

20. Interneurons in the Spine
Decisions made without the brain
Your spine’s interneurons
trigger your hand to pull
away from a fire before
you can say OUCH!
This is an example of a
reflex action.
The brain finds out
about the reflex after it
happens.

21. The Endocrine System
The
endocrine
system:
a set of
glands that
produce
chemical
messengers
called
hormones.

22. The Body’s “Slow but Sure”
Endocrine Message System
 The endocrine system sends
molecules as messages, just like the
nervous system, but it sends them
through the bloodstream instead of
across synapses.
 These molecules, called hormones,
are produced in various glands
around the body.
 The messages go to the brain and
other tissues.
Pituitary
gland
 The pituitary gland is the “master gland” of the endocrine
system.
 It is controlled through the nervous system by the nearby brain
area--the hypothalamus.
 The pituitary gland produces hormones that regulate other
glands.

23. Tools of Discovery
and Brain Structures
What We’ll See:
How we learn about
the brain:
 Scans and more
The primitive, life-
sustaining, inner parts
of the brain:
 The brainstem and
limbic system
Higher Brain structure
that help us think and
act:
 The Cerebral Cortex

24. Monitoring activity in the brain
Tools to read electrical, metabolic, and magnetic
activity in the brain:
EEG:
electroencephalogram
MRI: magnetic
resonance imaging
fMRI: functional MRI
PET: positron emission
tomography

25. 25
An EEG (electroencephalogram)
is a recording of the electrical
waves sweeping across the
brain’s surface.
An EEG is useful in studying
seizures and sleep.
EEG:
electroencephalogram

26. The PET scan allows us to see what
part of the brain is active by
tracing where a radioactive form
of glucose goes while the brain
performs a given task.
PET: positron emission
tomography

27. 27
MRI (magnetic resonance imaging)
makes images from signals produced by
brain tissue after magnets align the spin
of atoms.
The arrows below show ventricular
enlargement in a schizophrenic patient
(right).
MRI: magnetic
resonance imaging
Functional MRI reveals
brain activity and
function rather than
structures.
Functional MRI
compares successive
MRI images taken a
split second apart, and
shows changes in the
level of oxygen in
bloodflow in the brain.
fMRI: functional MRI

28. The Brain:
Less Complex Brain Structures
Our tour of the brain begins with parts of the human
brain found also in simpler animals; these parts
generally deal with less complex functions:
Brainstem (Pons and Medulla)
Thalamus
Reticular Formation
Cerebellum
Limbic System

29. The Brainstem:
Pons and Medulla

30. The Base of the
Brainstem:
The Medulla
 The medulla controls the most basic functions
such as heartbeat and breathing.
 Someone with total brain damage above the
medulla could still breathe independently, but
someone with damage in this area could not.

31. The Thalamus
 The thalamus is the
“sensory switchboard” or
“router”: All sensory
messages, except smell, are
routed through the
thalamus on the way to the
cortex (outer brain).
 These messages cross over
from one side of the body
to the opposite side of the
brain.
The
crossover

32. Reticular (“net-like”) Formation
 The reticular formation is a
nerve network in the
brainstem.
 It enables alertness
(arousal); stimulating this
makes us wide awake.
 It also filters incoming
sensory information and
relays it to other brain
areas.

33. The cerebellum
helps coordinate
voluntary
movement such as
playing a sport.
Cerebellum (“little brain”)
The cerebellum has many other
functions, including enabling
nonverbal learning and memory.

34.  emotions such as fear and
aggression.
 basic drives such as hunger and
sex.
 the formation of episodic
memories.
The hippocampus (“seahorse”)
 processes conscious, episodic
memories.
 works with the amygdala to
form emotionally charged
memories.
The Amygdala (“almond”)
 consists of two lima bean- sized
neural clusters.
 helps process emotions,
especially fear and aggression.
The Limbic (“Border”) System
The limbic system coordinates:

35. The Amygdala:
Enabling two different responses to threat
 Electrical stimulation
of one area of a cat’s
amygdala provokes
aggressive reactions.
 If you stimulate a
different part of the
amygdala and put the
cat in a cage with a
mouse, the cat will
cower in terror.

36.  lies below (“hypo”) the thalamus.
 regulates body temperature and
ensures adequate food and water
intake (homeostasis), and is
involved in sex drive.
 directs the endocrine system via
messages to the pituitary gland.
The Hypothalamus:
Thalamus
Riddle: Why did the rat
cross the grid?
Why did the rat want to
get to the other side?
The Hypothalamus as a Reward Center
Pushing the pedal that
stimulated the electrode
placed in the
hypothalamus was much
more rewarding than food
pellets.

37. Review of Brain Structures

38. Higher Brain, Split Brain
Topics for your cortex to process:
 Cerebral Cortex
Structure: The
Lobes
 The motor and
sensory strips and
association areas
 Brain Plasticity
 Functioning of he
right and left
hemispheres from
cases of the
divided and intact
brains

39. The Cerebral Cortex:
300 billion synaptic
connections
The brain has
left and right
hemispheres
 The outer grey “bark” structure that is wrinkled in order
to create more surface area for 20+ billion neurons.
 Organized into 4 lobes in each of two hemispheres.

40. 40
The Lobes of the Cerebral Cortex:
Preview
Frontal Lobes
Parietal Lobes
Occipital Lobes
Temporal Lobes
involved in speaking and muscle
movements and in making plans and
judgments
include the sensory cortex
include the visual areas; they
receive visual information from
the opposite visual field
include the auditory processing
areas

41. Input: Sensory
cortex (Left
hemisphere
section receives
input from the
body’s right side)
Output: Motor
cortex (Left
hemisphere
section
controls the
body’s right
side)
Functions of the Brain:
The Motor and Sensory Strips
 Axons
receiving motor
signals FROM
the cortex
Axons
sending
sensory
information
TO the cortex

42. Sensory Functions of the Cortex
 The sensory strip deals
with information from
touch stimuli.
 The occipital lobe deals
with visual information.
 Auditory information is
sent to the temporal
lobe.

43. The Visual Cortex
This fMRI scan
shows
increased
activity in the
visual cortex
when a person
looks at a
photograph.

44. Association function of the cortex
More complex animals have more cortical space
devoted to integrating/associating information

45. Case study: Phineas Gage
In a work accident, a metal rod
shot up through Phineas Gage’s
skull, destroying his eye and part
of his frontal lobes.
After healing, he was rude, odd,
irritable, and unpredictable.
Possible explanation for the
change in personality:
Damage to his frontal lobes hurt
his ability to inhibit emotions and
impulses.

46. Whole-brain Association Activity
Whole-brain association
activity involves complex
activities which require
communication among
association areas across the
brain such as:
 memory
 language
 attention
 meditation and spirituality
 consciousness

47. This 6-year-old had a
hemispherectomy to end life-
threatening seizures; her
remaining hemisphere
compensated for the damage.
Plasticity: The Brain is Adaptable
If the brain is damaged,
especially in the general
association areas of the cortex:
 the brain does not repair
damaged neurons, BUT it can
restore some functions
 it can form new connections,
reorganize, reassign brain
areas to new functions.
 Some neurogenesis,
production of new brain cells,
helps rebuild

48. Brain Studies
Researchers have studied the
impact of this surgery on
patients’ functioning.
Split-
To end severe
whole-brain
seizures, some
people have had
surgery to cut the
corpus callosum,
a band of axons
connecting the
hemispheres.

49. Separating the Hemispheres:
Factors to Keep in Mind
 Each hemisphere controls the opposite side of
the body AND is aware of the visual field on
that opposite side.
 Without the corpus callosum, the halves of
the body and the halves of the visual field do
not work together.
 Only the left half of the brain has enough
verbal ability to express its thoughts out loud.

50. Split visual field
Each hemisphere
perceives the half of the
view in front of you that
goes with the half of the
body that is controlled
by that hemisphere.

51. 51
Divided Awareness in the Split Brain
Try to explain the following result:

52. The divided brain in action
 Talent: people
are able to
follow two
instructions and
draw two
different shapes
simultaneously
 Drawback:
people can be
frustrated that
the right and left
sides do
different things

53. Our Two
Hemispheres
Lateralization (“going to one side”)
The two hemispheres serve some different functions.
How do we know about these differences?
 Brain damage studies revealed many functions of
the left hemisphere.
 Brain scans and split brain studies show more about
the functions of the two hemispheres, and how they
coordinate with each other.

54. • Thoughts
and logic
• Language:
words and
definitions
• Pieces and
details
• Feelings
and
intuition
• Language:
tone,
inflection,
context
• Wholes,
including
the self
The intact but lateralized brain
Right-Left Hemisphere Differences
Left Hemisphere Right Hemisphere

55. Behavior Genetics and Evolutionary
Psychology

56. Behavior Genetics:
Predicting Individual Differences
More ways of exploring the
origins of the biology of
behavior:
1. Understanding genes
2. Twin and adoption
studies
3. Gene/environment
interactions
4. Evolutionary
Psychology
Behavior geneticists
study how heredity
and environment
contribute to
human differences.
Let’s start by looking
at GENES.

57. Genes are
parts of DNA
molecules,
which are
found in
chromosomes
in the nuclei of
cells.
DNA
(Deoxyribonucleic Acid)
GENES:
The Building Blocks of
Heredity and
Development
Genes are
parts of DNA
molecules,
which are
found in
chromosomes
in the nuclei of
cells.
GENES:
The Building Blocks of
Heredity and
Development

58. Chromosomes are made of DNA,
which are made of genes.
}
Chromosome:
threadlike structure
made largely of DNA
molecules
DNA:
a spiraling, complex
molecule containing
genes

59. Chromosomes and Inheritance
 The human genome includes 46
chromosomes in 23 sets
matched sets; each
chromosome has the same
gene locations.
 This includes the X and Y
chromosomes, not a matched
set in males, who are missing
some genes on the Y.
 A biological parent donates half
his/her set of chromosomes to
his/her offspring.
 We received half a set of
chromosomes from each
biological parent.

60. The Human Genome:
20,000 to 25,000 Genes
 Human genomes are so nearly
identical that we can speak of
one universal human genome.
 Yet tiny genetic differences
make a difference. If there is a:
 .001 percent difference in
genome, your DNA would
not match the crime
scene/you are not the
baby’s father.
 0.5 to 4 percent difference
in genome, you may be a
chimpanzee.
 50 percent difference in
genome, you may be a
banana.
The genome: an
organism’s entire
collection of genes

61. How Genes Work
 Genes are not blueprints;
they are molecules.
 These molecules have
the ability to direct the
assembly of proteins that
build the body.
 This genetic protein
assembly can be turned
on and off by the
environment, or by other
genes.
 Any trait we see is a
result of the complex
interactions of many
genes and countless
other molecules.

62. Or vary the genes in the
same environment?
Next step for behavior geneticists:
Controlling Variables
Can we design an
experiment to keep genes
constant and vary the
environment and see what
happens?

63. Twin and
Adoption Studies
To assess the
impact of nature
and nurture, how
do we examine
how genes make a
difference within
the same
environment?
 study traits of
siblings vs.
identical twins
 see if the
siblings vary
more than
twins
Fraternal and Identical Twins
Fraternal “twins” from separate eggs
are not any more genetically alike than
other siblings.
Identical twin: Same sex only
Fraternal twin: Same or opposite sex

64. Twin and
Adoption Studies
How do we find
out how the same
genes express
themselves in
different
environments?
We can study the
traits of identical
twins as they grow
up, or if they were
raised separately
(e.g., the
Minnesota Twin
Family Study).
Identical vs. Fraternal Twins
Studies of twins in adulthood show
that identical twins are more alike than
fraternal twins in:
 personality traits such as
extraversion (sociability) and
neuroticism (emotional instability).
 behaviors/outcomes such as the
rate of divorce.
 abilities such as overall Intelligence
test scores.

65. Critiques of Twin Studies
1. In the more recent years of the
Minnesota Twin Family Study, twins
have known about each other and
may influence each other to be
more similar.
2. Coincidences happen; some
randomly chosen pairs of people will
have similar traits.
3. Environments may be similar;
adoptive families tend to be more
similar than randomly selected
families in education, income, and
values.
Studies of Identical Twins Raised Apart
Similarities found in
identical twins despite
being raised in different
homes:
 personality, styles of
thinking and relating
 abilities/intelligence
test scores
 attitudes
 interests, tastes
 specific fears
 brain waves, heart
rate
BUT none of these factors explains,
better than the genetic explanation,
why fraternal twins have more
differences than identical twins.

66. Searching for Parenting Effects:
Biological vs. Adoptive Relatives
Studies have been performed with adopted children for
whom the biological relatives are known.
Findings: Adopted children seem to be more similar to
their genetic relatives than their environmental/nurture
relatives.
Given the evidence of genetic impact
on how a person turns out,
does parenting/nurture
make any difference?
Does the home environment have any
impact?

67. Despite the strong impact of
genetics on personality,
parenting has an influence on:
 religious beliefs
 values
 manners
 attitudes
 politics
 habits
Parenting Does Matter

68.  Gene-Environment
Interaction: genes turn
each other on and off in
response to
environmental
conditions
 Epigenetics: The study
of how this happens:
The environment acts
on the surface of genes
to alter their activity
How does the interaction of genes
and environment work?
Example in
animals:
shortened daylight
triggers animals to
change fur color or
to hibernate
Example in
humans:
obesity in adults
can turn off weight
regulation genes in
offspring

69. 69
Some topics:
 Natural selection and
adaptation
 Evolutionary success may help
explain similarities
 An evolutionary explanation
of human sexuality
Evolutionary Psychology:
Understanding Human Nature
Evolutionary
psychology is the
study of how
evolutionary
principles help explain
the origin and
function of the human
mind, traits, and
behaviors.
We have been talking so far about
human differences; we may now
seek insight in the ways in which
humans are alike.

70. Begin with a
species’ genome,
which contains a
variety of
versions of genes
that shape traits.
Conditions make it
difficult for
individuals with
some traits (some
versions of those
genes) to survive
long enough to
reproduce.
Other individuals
thus have their
traits and genes
“selected” to
spread in the
population.
Evolutionary Psychology:
Natural Selection: How it Works

71. 71
 Dmitri Balyaev and
Lyudmila Trut spent
40 years selecting
the most gentle,
friendly, and tame
foxes from a fox
population, and
having those
reproduce.
 As a result, they
were able to shape
avoidant and
aggressive creatures
into social ones, just
as wolves were once
shaped into dogs.
Artificial Selection
The Domesticated Silver Foxes

72. 72
Example:
 Why does “stranger anxiety”
develop between the ages of 9
and 13 months?
Hint: in evolutionary/survival
terms, humans are learning to
walk at that time.
Infants who used their new
ability to walk by walking away
from family and toward a lion
might not have survived to
reproduce as well as those who
decided to stay with parents
around the time they learned
to walk.
How might evolution have shaped
the human species?

73. 73
 Why do people so easily
acquire a phobia of
snakes, more easily than a
phobia of cars?
 An evolutionary
psychologist would note
that snakes are often
poisonous…
…so, those who more
readily learned to fear
them were more likely to
survive and reproduce.
Evolutionary Psychology’s Explanation of
Biologically Driven Phobias

74. Critiquing Evolutionary Psychology
“You’re just
taking current
reality and
constructing a
way you could
have predicted
it.” This is
hindsight
reasoning and
unscientific.
“You’re
attributing too
much to genes
rather than the
human ability to
make choices
about social
behavior.”
Response: yes, but there
are predictions made
about future behavior
using this reasoning.
Response: yes, but our
evolutionary past does not
prevent our ability to act
differently; “is” does not
equal “ought.”

75. Evolution: Theory
 Evolution is a scientific theory
(NOT a “guess” and not a
hypothesis, but something
more): a coherent set of
principles that fits very well
with the accumulated evidence.
 Parts of the evolutionary story
may conflict with other stories
of origins and change over
time.
 Is there room for overlap and
agreement?
Possible areas of
consensus, with or
without evolution:
 The human mind
and body seems
almost “designed,”
by evolution or
other forces, to
have certain traits
and abilities.
 Nurture may shape
us, but we seem to
start out with some
sort of human
nature.