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Chapter 3: The Biological Bases
of Behavior
Biology & Behavior
 Evidence over that past few decades has highlighted
the power effects biology plays into our behavior.
 Much more complex than mere cause and effect, as
multiple systems work simultaneously within the
body.
Communication in the Nervous System
 Your nervous system is living tissue composed of
cells that fall into two major categories: glial and
neurons.
 Neurons are individual cells in the nervous system
that receive, integrate, and transmit information.
The Structure and Function of Neurons
Neurons process and transmit information
•

Two types of branches extend from the cell body: axons and
dendrites
Structure of Neuron
 Soma, or cell body, contains the cell nucleus & much of
the chemical machinery common to most cells.
 Dendrites are the parts of a neuron that are specialized
to receive information.
 The axon is a long, thin fiber that transmits signals away
from the soma to other neurons or to muscles or glands.
Structure of Neuron (con’t)
 The myelin sheath is insulating material that
encases some axons.
 Axons end in a cluster of Terminal buttons, which
are small knobs that secrete chemicals called
neurotransmitters.
 Synapse is a junction where information is
transmitted from one neuron to another.
The Structure and Function of Neurons
Neurons process and transmit information
•

Two types of branches extend from the cell body: axons and
dendrites
Glial Cells
 Found throughout the nervous system
 Glia (literally “glue”) tend to be much smaller than
neurons, but are in equeal amounts. .
 Appear to account for over 50% of the brain’s
volume.
 Supply nourishment, help remove waste products, &
provide insulation around many axons.
Glial Cells (con’t)
 Glia play complicated role in development of nervous
system in human embryo.
 Myelin sheaths that encase some axons are derived
from special types of glial cells.
Glial Cells and the Blood-Brain Barrier
Glia Form Myelin
•
The myelin sheath insulates axons and speeds
electrical transmission along axons
The Neural Impulse: Using
Energy to Send Information
How Neurons Work
 Information is received at the dendrites, is passed
through the soma (cell body) to the branches ends of
axon.
 Then transmitted to the dendrites of other cells at
meeting points called synapses, where
neurotransmitters are released from terminal
buttons.
Axons Transmit Information
Neural Communication: A Two-Step Process
•
•
Electrical signaling: action potential
Chemical signaling: neurotransmitters
The Neuron at Rest: A Tiny Battery
 Neural impulse is a complex electrochemical
reaction (Hodgkin and Huxley ,1952).
 The neural impulse is a brief change in a neuron’s
electrical charge that moves along an axon.
 The resting potential of a neuron is its stable,
negative charge when the cell is inactive.
The Action Potential
 Triggers the release of chemicals called
neurotransmitters that diffuse across a synapse to
communicate with other neurons.
 Like a spark traveling along a trail of gunpowder, the
voltage change races down the axon.
Generating an Action Potential
Electrical Signaling: Propagating an Action
Potential
The All-or-None Law
 The neural impulse is an all-or-none proposition,
like firing a gun. You can’t half-fire a gun.
 Either the neuron fires or it doesn’t, and its action
potentials are all the same size ( Kandel, 2000).
 Weaker stimuli do not produce smaller action
potentials and stronger stimuli do not evoke larger
action potentials.
Sending Signals: Chemicals as Couriers
 Neuron that sends a signal = presynaptic neuron
 neuron that receives = postsynaptic neuron.
 Arrival of action potential triggers the release of
neurotransmitters—chemicals that transmit
information from one neuron to another.
Chemical Signaling: Releasing
Neurotransmitters
Receiving Signals: Postsynaptic Potentials
 When a neurotransmitter & receptor molecule
combine, reactions in cell membrane cause a
postsynaptic potential (PSP), a voltage change at
a receptor site on a postsynaptic cell membrane.
Receiving Signals: Postsynaptic Potentials
 Two types of messages can be sent from cell to cell:
excitatory and inhibitory.

An excitatory PSP is a positive voltage shift that increases the
likelihood that the postsynaptic neuron will fire action
potentials.

An inhibitory PSP is a negative voltage shift that decreases the
likelihood that the postsynaptic neuron will fire action
potentials.
Receiving Signals: Postsynaptic Potentials
(con’t)
 Once synaptic activity is complete, reuptake occurs
when neurotransmitters are sponged up from the
synaptic cleft by the presynaptic membrane.
Communicating Through the Synapse
Overview of Synaptic Transmission
Synapses & Neural Pathways
Neurotransmitters and
Behavior
NEUROTRANSMITTERS ARE FUNDAMENTAL TO
BEHAVIOR, PLAYING A KEY ROLE IN EVERYTHING
FROM MUSCLE MOVEMENTS TO MOODS AND
MENTAL HEALTH.
Acetylcholine (ACh)
 Plays a key role in muscular movement.
 Contributes to the regulation of attention, arousal, and
memory.
 Disoder associated with imbalance of
Ach = Alzheimer’s.

Source: Microsoft ClipArt
Monoamines: Dopamine (DA)
 Dopamine (DA) contributes to control of voluntary
movement.

Cocaine and amphetamines elevate activity at DA synapses

Dopamine circuits in medial forebrain bundle characterized as
“reward pathway”
 Disorders from imbalance of DA: Parkinson's,
schizophrenic disorders & addictive disorders
Monoamines: Norepinephrine (NE)
 Contributes to modulation of mood and arousal.
 Cocaine and amphetamines elevate activity at NE
synapses.
 Disorders from imbalance = Depressive disorders
Monoamines: Serotonin
 Involved in regulation of sleep and wakefulness,
eating, aggression
 Antidepressant drugs affect serotonin circuits
 Disorders from imbalance = depressive, obsessive-
compulsive & eating disorders.
GABA
 Serves as widely distributed inhibitory transmitter,
contributing to regulation of anxiety & sleep/arousal
 Valium and similar antianxiety drugs work at GABA
synapses
 Disorder from imbalance = Anxiety disorders
Endorphins
 Resemble opiate drugs in structure and effects
 Play role in pain relief and response to stress
 Contribute to regulation of eating behavior
 May underlie the experience of the “runner’s
high.”

Source: Microsoft ClipArt
Organization of the
Nervous System
The Organization of the Nervous System
The Spinal Cord
The Spinal Nerves and Reflexes
The Central Nervous System
 CNS is bathed in cerebrospinal fluid,
which provides a protective cushion.
The Peripheral Nervous System
 Consists of the nerves that lie outside the brain and
spinal cord.
 Subdivided into:

somatic nervous system = connects to muscles and sensory
receptors

autonomic nervous system = connects to blood vessels, smooth
muscles, and glands.
The Somatic Nervous System and the Cranial
Nerves
The Peripheral Nervous System (con’t)
 autonomic nervous system controls the largely automatic
arousal that accompanies emotion & is divided into

sympathetic

parasympathetic
 Cannon (1932) called it the fight-or-flight response =
organisms generally respond to threat by preparing
physically for attacking (fight) or fleeing (flight) the
enemy.
Fight or Flight Response Redefined
 Human stress response is an elaborate and complex
psychobiological series of reactions designed for
coping, adaptation, & survival of both the individual
and the species.
 Theory has expanded to include fight, flight, freeze,
or faint as the most likely behaviors induced in the
stress response (Bracha, 2004).
Human Stress Response
 Taylor (2000) addressed gender imbalances in
research by exploring how women react to stress.
 She suggested “tend and befriend” is more accurate
description of how, when women see another person
in distress, they will circle the wagons using
friendship to tend to the person.
 More recent studies show this is not gender specific.
The Autonomic Nervous System and
Homeostasis
The Brain and Behavior
Looking Inside the Brain: Research
Methods
 Lesioning involves destroying a piece of the brain to
see the effect on behavior.
 CT scans and MRI scans provide images of brain
structure.
 PET scans and fMRI scans can track brain activity.
The
Brain
Divided
Source: Microsoft ClipArt
The Brain Divided
The Hindbrain
 The medulla regulates functions such as breathing
and circulation
 The cerebellum is involved in movement and
balance
 The pons contributes to sleep and arousal.
The Midbrain
 Segment of the brainstem that lies between the
hindbrain and the forebrain.
 Contains an area that is concerned with integrating
sensory processes, such as vision and hearing ( Stein,
Wallace, & Stanford, 2000).
The Forebrain
 The largest & most complex region of the brain.
 Houses a variety of structures including the
thalamus, hypothalamus, limbic system, and
cerebrum
 All three structures are located near the top of the
brainstem.
The Thalamus: A Relay Station
 A structure in the forebrain through which all
sensory information (except smell) must pass to get
to the cerebral cortex.
 Appears to play an active role in integrating
information from various senses.
The Hypothalamus: A Regulator of
Biological Needs
 A structure found near the base of the forebrain that
is involved in the regulation of basic biological needs
 Plays a major role in the regulation of basic
biological drives related to survival, including the socalled “four F’s”: fighting, fleeing, feeding, and
fornicating.
The Limbic System: The Seat of Emotion
 A loosely connected network of structures located
roughly along the border between the cerebral cortex
and deeper subcortical areas.
 Includes parts of the thalamus & hypothalamus, the
hippocampus, the amygdala, and other nearby
structures.
The Limbic System (con’t)
 hippocampus & adjacent structures clearly play a
role in memory processes
 In essence, this is the part of the brain that processes
our experiences through our inner storyline.
The Limbic System (con’t)
 Amygdala may play a central role in the learning of
fear responses and the processing of other basic
emotional responses.
 The limbic system also appears to contain emotion-
tinged “pleasure centers.”
The Cerebrum: The Seat of Complex
Thought
 Cerebrum = largest and most complex part of the
brain.
 Includes brain areas responsible for our most
complex mental activities, including learning,
remembering, thinking, and consciousness itself.
The Cerebrum: The Seat of Complex
Thought
 The cerebral cortex is the convoluted outer layer of
the cerebrum. The cortex is folded and bent, so that
its large surface area—about 1.5 square feet—can be
packed into the limited volume of the skull.
 The cerebrum is divided into two halves called
hemispheres.
The Cerebrum: The Seat of Complex
Thought
 The corpus callosum is the major structure that
connects the two cerebral hemispheres
The Cerebrum: The Seat of Complex
Thought
 Each cerebral hemisphere is divided by deep fissures
into four parts called lobes.
 Lobes & their primary known functions:

occipital lobe (vision),

parietal lobe (touch),

temporal lobe (hearing),

frontal lobe (movement of the body)
The Cerebrum: Mirror Neurons
 Neurons activated by performing an action or by
seeing another monkey or person perform the same
action.
 Mirror neurons appear to provide a new model for
understanding complex social cognition at a neural
level.
 New findings suggest mirror neurons may play a
fundamental role in the acquisition of new motor
skills
The Cerebrum: Prefrontal Cortex
 disproportionately large in humans, accounting for
about one-third of the cerebral cortex.
 Contributes to certain types of decision making as
some sort of “executive control system,” which is
thought to monitor, organize, and direct thought
processes.
 Affected functions include problem solving, delaying
gratification, planning, compassion & higher order
reasoning.
Plasticity of the Brain
 Neuroplasticity - anatomical structure and functional
organization of the brain are more flexible or
“plastic” than widely assumed.
 Neurogenesis—the formation of new neuron
Neuroplasticity
Right Brain/Left Brain
CEREBRAL SPECIALIZATION
Hemispheric Specialization in the Intact
Brain
 Two sides of the brain are in constant
communication.
 Newer brain imaging methods map fluid
communication networks in the brain

Revealing a highly dynamic interhemispheric communication
& coordination (Doron, Bassett, & Gassaniga, 2012).

Images of Einstein’s brain reveal exceptional degree of
connectivity btwn right & left hemispheres.
The Endocrine System: Another Way to
Communicate
 Endocrine system = system of glands that secrete
hormones into the blood stream that help control
bodily functioning.
 Hormone release tends to be pulsatile (released
several times per day in brief bursts that last only a
few minutes).
The Endocrine System
 Oxytocin—a hormone released by pituitary, that
regulates reproductive behaviors.
 Fosters bonding, empathy, and trust.
The Endocrine System
 Much of the endocrine system is controlled by the
nervous system through the hypothalamus connected to
the pituitary gland.
 Pituitary gland releases variety of hormones that fan out
within the body, stimulating actions in the other
endocrine glands.
 Pituitary is the “master gland” of the endocrine system.
The Pituitary Gland
The Endocrine Glands
Heredity and Behavior
IS IT ALL IN THE GENES?
Basic Principles of Genetics
 Chromosomes are threadlike strands of DNA
(deoxyribonucleic acid) molecules that carry genetic
information.
 Genes are DNA segments that serve as the key
functional units in hereditary transmission.
Genes, Chromosomes, and DNA
Basic Principles of Genetics
 The basic units of genetic transmission are pairs of
genes housed on chromosomes, which can be
scrambled in an endless variety of ways.
 The key to the concept of genetic relatedness is that
closer relatives share a larger proportion of genes
than more-distant relatives.
Basic Principles of Genetics
 Like chromosomes, genes operate in pairs, with one
gene of each pair coming from each parent.
 Most behavioral qualities appear to involve polygenic
inheritance, which means that many pairs of genes
play a role in influencing the traits.
Detecting Hereditary Influence: Research
Methods
 Family studies evaluate hereditary influence by
examining blood relatives to see how much they
resemble one another on a specific trait.
 Adoption studies assess hereditary influence by
examining the resemblance between adopted
children and both their biological and their adoptive
parents.
Detecting Hereditary Influence: Research
Methods
 Twin studies estimate hereditary influence by
comparing the resemblance of identical twins and
fraternal twins with respect to a trait.
 Twin studies generally can provide the strongest
evidence.
The Interplay of Heredity and
Environment
 Epigenetics = study of heritable changes in gene
expression that do not involve modifications to the
DNA sequence.
 New work in epigenetics has further demonstrated
that genetic and environmental factors are deeply
intertwined.
The Evolutionary Bases of Behavior
 Evolutionary psychology = theory that analyzes
behavioral processes in terms of their adaptive
significance.
Darwin’s Insights
 Darwin argued that if a heritable trait contributes to
an organism’s survival or reproductive success,
organisms with that trait should produce more
offspring than those without the trait & the
prevalence of that trait should gradually increase
over generations-thanks to natural selection.
Darwin’s Insights
 Fitness refers to organisms’ reproductive success.
 Variations in reproductive success are what really
fuels evolutionary change.

Source: Microsoft ClipArt
Later Refinements to Evolutionary Theory
 An adaptation is an inherited characteristic that
increased in a population (through natural selection)
because it helped solve a problem of survival or
reproduction during the time it emerged.
Later Refinements to Evolutionary Theory
 Because of the incremental nature of evolution,
adaptations sometimes linger in a population even
though they no longer provide a survival or
reproductive advantage.
 Examples of behaviors sculpted by evolution include
eating behavior, the avoidance of predators, and
mating strategies.
Behaviors as Adaptive Traits
 Modern evolutionary psychology is based on the
well-documented assumption that a species’ typical
patterns of behavior often reflect evolutionary
solutions to adaptive problems.