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The Biological Basis of
Behavior
Chapter 2
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Neurons: The Messengers
About 100 billion neurons (nerve cells) in
the human brain
 Neurons have many of the same features
as other cells

Nucleus
 Cytoplasm
 Cell membrane


What makes neurons unique is their shape
and function
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Structure of Neurons

Dendrites


Cell Body (Soma)


Contains nucleus
Axon


Carry information to the cell
body from other neurons
Carries information to the
next cell
Myelin Sheath

Insulates the axon and
speeds up the neural
impulse
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Types of Neurons

Sensory neurons



Motor neurons



Carry information from sensory systems to the brain
Also referred to as afferent
Carry information from the brain to muscles and
glands
Also referred to as efferent
Interneurons

Carry information between other neurons
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Glial Cells
Cells that insulate and support neurons
 Create the myelin sheath
 Remove waste products
 Provide nourishment
 Prevent harmful substances from entering
the brain

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Neural Impulse
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Neural Impulse

Ions


Charged molecules
Resting Potential



When more negative
ions are inside the
neuron than outside
Charge is
approximately -70mV
Neuron is not
transmitting
information
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Neural Impulse

Polarization


When the electrical charge of a cell moves
away from zero
Depolarization

When the electrical charge of a cell moves
toward zero
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Neural Impulse

Action Potential



Sudden, massive
change in charge in
the neuron
Occurs when
depolarization reaches
the threshold of
excitation
Ions flow across cell
membrane
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Neural Impulse

Graded Potentials
Subthreshold depolarization
 Many subthreshold depolarizations are added
together to produce an action potential (a
process known as summation)

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Neural Impulse

All-or-None Law
A neuron either fires or it does not
 When it does fire, it will always produce an
impulse of the same strength
 Intensity of a stimulus is coded by the
frequency of action potentials

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Neural Impulse

Absolute refractory period


Period immediately after an
action potential when
another action potential
cannot occur
Relative refractory period

Period following absolute
refractory period when a
neuron will only respond to
a stronger than normal
impulse
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Synapse

Synaptic space (synaptic cleft)


Terminal button


Tiny gap between neurons
Enlarged area at the end of an axon
The synapse

Composed of the terminal button of one
neuron, the synaptic space, and the dendrites
or cell body of the receiving neuron
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Transmission Between Neurons

Synaptic vesicles


Neurotransmitters


Sacs in terminal button
that release chemicals
into synaptic space
Chemicals released by
synaptic vesicles
Receptor sites

Location on receptor
neuron for specific
neurotransmitter
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Some Well-Known
Neurotransmitters

Acetylcholine (ACh)




Released at the neuromuscular junction
Plays an important role in arousal and attention
Loss of ACh producing cells is linked to Alzheimer’s
Disease
Dopamine



Affects neurons associated with voluntary movement
Plays a role in learning, memory, and emotions
Loss of dopamine-producing cells causes symptoms
of Parkinson’s Disease
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Some Well-Known
Neurotransmitters

Serotonin
Found throughout the brain
 Appears to sets an “emotional tone”
 Low serotonin levels are implicated in
depression


Endorphins

Reduce pain by inhibiting or “turning down”
neurons that transmit pain information
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Psychopharmacology
Most psychoactive drugs (and toxins) work
by blocking or enhancing synaptic
transmission
 Botulism

Blocks release of ACh at the neuromuscular
junction, causing paralysis
 “Botox” is botulism toxin used to prevent facial
muscles from making wrinkles

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Psychopharmacology

Curare



Antipsychotic medications



Can stun or kill prey quickly
Blocks ACh receptors causing paralysis
Block dopamine receptors
Reduces schizophrenic hallucinations
Caffeine

Increases the release of excitatory neurotransmitters
by blocking the inhibitory neurotransmitter adenosine
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Psychopharmacology

Cocaine
Prevents reabsorption of dopamine
 Leads to heightened arousal of entire nervous
system

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Neural Plasticity
The brain can be changed, both
structurally and chemically, by experience
 Rat studies show that an “enriched”
environment leads to larger neurons with
more connections
 Has also been shown in humans
 Recent research has uncovered evidence
of neurogenesis, or the production of new
brain cells, in human brains

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Nervous System Organization

Central nervous
system (CNS)


Consists of the brain
and spinal cord
Peripheral nervous
system

Connects the CNS to
the rest of the body


Somatic nervous
system
Autonomic nervous
system
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Central Nervous System
Central Nervous System
Brain
Spinal Cord
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Brain – The Central Core

Medulla


Pons


Controls breathing,
heart rate, and blood
pressure
Maintains the sleepwake cycle
Cerebellum

Coordinates body’s
movements
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Brain – The Central Core

Thalamus


Relays information from
sensory receptors to the
brain
Hypothalamus



Influences motivated
behavior
Regulates hunger, thirst,
body temperature, and
sexual drive.
Directly involved in
emotional behavior
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Brain – The Central Core

Reticular formation
Network of neurons found throughout the
brain
 Serves to alert and arouse higher brain in
response to incoming information

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Brain – The Limbic System


Ring of structures located
between the central core
and the cerebral
hemispheres
Important to learning and
emotional behavior


Hippocampus essential in
formation of new memories
Amygdala, together with
the hippocampus, is
important for regulating
emotions
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Cerebral Cortex

Occipital lobe


Receives and processes
visual information
Temporal lobe




Complex visual tasks such
as face recognition
Receives and processed
auditory information
Involved in balance, some
emotions and motivations
Some language processing
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Cerebral Cortex

Parietal lobe



Receives sensory
information from body
Involved in spatial abilities
Frontal lobe


Coordinated information
from other lobes
Controls voluntary
movement, attention,
setting goals, and
expression of appropriate
emotions
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Hemispheric Specialization

Corpus Callosum



Fibers that connect the
two hemispheres
Allow close
communication
between left and right
hemishphere
Each hemisphere
appears to specialize
in certain functions
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Split-Brain Research

Much information about functions of each
hemisphere has come from studying splitbrain patients
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Tools for Studying the
Nervous System
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Microelectrode Techniques
Very small electrodes inserted into
individual neurons
 Used to study activity of a single neuron

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Macroelectrode Techniques
Used to get a picture of overall activity in
the brain
 An example is an EEG, which uses
electrodes placed on a person’s scalp to
measure brain activity

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Structural Imaging

Computerized Axial Tomography (CTscan)


Uses X-rays to create a 3-dimensional image
of the brain
Magnetic Resonance Imaging (MRI)

Uses a magnetic field and radio waves to
produce images
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Functional Imaging

EEG imaging


electrical activity on the scalp from millions of
neurons is used to produce a continuous
picture of activity in the brain
Magentoencephalography (MEG) and
Magnetic source imaging (MSI)

Can localize activity more precisely than EEG
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Functional Imaging

Positron Emission Tomography (PET) and
Single Photon Emission Computed
Tomography (SPECT)


Use radioactive glucose to determine location
of greatest brain activity
Functional Magnetic Resonance Imaging
(fMRI)

Shows function and structure by measuring
movement of blood molecules within the brain
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Spinal Cord
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Spinal Cord
Complex cable of nerves that connects
brain to rest of the body
 Carries motor impulses from the brain to
internal organs and muscles
 Carries sensory information from
extremities and internal organs to the brain

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Spinal Cord

The spinal cord controls some protective
reflex movements without any input from
the brain
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Peripheral Nervous System
Peripheral Nervous System
Somatic Nervous System
Autonomic Nervous System
Sympathetic Division
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Parasympathetic Division
The Somatic Nervous System
Consists of neurons that communicate
between the body and the brain
 Afferent neurons



Neurons that carry messages from sense
organs to spinal cord
Efferent neurons

Neurons that carry messages from the spinal
cord or brain to muscles and glands
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Autonomic Nervous System

Sympathetic division




Most active when you
are angry, afraid, or
aroused
Fight-or-flight
response
Increases heart rate
and breathing
Stops digestion
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Autonomic Nervous System

Parasympathetic
division




Calms body
Produces effects
opposite to those of
the sympathetic
division
Reduces heart rate
and breathing
Restores digestion
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Endocrine System
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Endocrine System
Helps coordinate and integrate complex
psychological reactions
 Endocrine glands secrete hormones into
the bloodstream
 Hormones serve to organize the nervous
system and body
 Hormones also activate behavior, such as
sexual behavior

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Endocrine System

Thyroid gland


Secretes hormones
(primarily thyroxin) that
control metabolism
Parathyroid glands

Control levels of
calcium and
phosphate which in
turn controls levels of
excitability
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Endocrine System

Pineal gland


Secretes melatonin
which regulates the
sleep-wake cycle
Pancreas


Regulates blood-sugar
levels
Secretes insulin and
glucagon
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Endocrine System

Pituitary gland


Gonads


Referred to as the
“master gland”
because it regulates
many other glands
Ovaries and testes
secrete estrogens and
androgens
Adrenal glands

Secretes hormones in
Psychology: An Introduction
reaction to stressCharles
A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Genes, Evolution, and
Behavior
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Genetics
Heredity - transmission of trait from one
generation to next
 Chromosomes



Pairs of thread like bodies that contain genes
Deoxyribonucleic acid (DNA)
Organic molecule arranged in a double-helix
 Contains the “code of life”

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Behavior Genetics
Study of behavior from a genetic
perspective
 Animal behavior genetic studies include:

Strain studies
 Selection studies

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Human Behavior Genetics

Family studies
Assume that close family members share
more of a trait than non-relatives
 Used to assess the heritability of
psychological disorders or traits


Twin studies
Used to determine how heritable a trait or
disorder may be
 Identical twins would have highest heritability

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Human Behavior Genetics

Adoption studies


Used to assess the influence of environment
Molecular genetics

Direct study of the genetic code
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Evolutionary Psychology

Natural selection


“Survival of the fittest”
Evolutionary psychology looks at the
adaptive or survival value of behaviors
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Social Implications
Study of biological origins of behavior
could lead to genocide and eugenics
aimed at eliminating certain types of
people
 Could also be used to create new
categories of people, such as people bred
to be good soldiers or manual laborers

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
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