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Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Biological Basis of
Behavior
Chapter 2

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

Structure of Neurons
 Dendrites
 Carry information to the cell
body from other neurons
 Cell Body (Soma)
 Contains nucleus
 Axon
 Carries information to the
next cell
 Myelin Sheath
 Insulates the axon and
speeds up the neural
impulse

Types of Neurons
 Sensory neurons
 Carry information from sensory systems to the brain
 Also referred to as afferent
 Motor neurons
 Carry information from the brain to muscles and
glands
 Also referred to as efferent
 Interneurons
 Carry information between other neurons

Glial Cells
 Cells that insulate and support neurons
 Create the myelin sheath
 Remove waste products
 Provide nourishment
 Prevent harmful substances from entering
the brain

The Neural Impulse

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

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

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

The Neural Impulse
 Graded Potentials
 Subthreshold depolarization
 Many subthreshold depolarizations are added
together to produce an action potential (a
process known as summation)

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

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

The Synapse
 Synaptic space (synaptic cleft)
 Tiny gap between neurons
 Terminal button
 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

Transmission Between Neurons
 Synaptic vesicles
 Sacs in terminal button
that release chemicals
into synaptic space
 Neurotransmitters
 Chemicals released by
synaptic vesicles
 Receptor sites
 Location on receptor
neuron for specific
neurotransmitter

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

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

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

Psychopharmacology
 Curare
 Can stun or kill prey quickly
 Blocks ACh receptors causing paralysis
 Antipsychotic medications
 Block dopamine receptors
 Reduces schizophrenic hallucinations
 Caffeine
 Increases the release of excitatory neurotransmitters
by blocking the inhibitory neurotransmitter adenosine

Psychopharmacology
 Cocaine
 Prevents reabsorption of dopamine
 Leads to heightened arousal of entire nervous
system

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

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

Central Nervous System
Central Nervous System
Brain Spinal Cord

The Brain – The Central Core
 Medulla
 Controls breathing,
heart rate, and blood
pressure
 Pons
 Maintains the sleep-
wake cycle
 Cerebellum
 Coordinates body’s
movements

 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

 Reticular formation
 Network of neurons found throughout the
brain
 Serves to alert and arouse higher brain in
response to incoming information

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

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

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

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

Split-Brain Research
 Much information about functions of each
hemisphere has come from studying split-
brain patients

Tools for Studying the
Nervous System

Microelectrode Techniques
 Very small electrodes inserted into
individual neurons
 Used to study activity of a single neuron

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

Structural Imaging
 Computerized Axial Tomography (CT-
scan)
 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

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

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

The Spinal Cord

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

The Spinal Cord
 The spinal cord controls some protective
reflex movements without any input from
the brain

The Peripheral Nervous System
Peripheral Nervous System
Somatic Nervous System Autonomic Nervous System
Sympathetic Division 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

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

The Autonomic Nervous System
 Parasympathetic
division
 Calms body
 Produces effects
opposite to those of
the sympathetic
division
 Reduces heart rate
and breathing
 Restores digestion

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

 Thyroid gland
 Secretes hormones
(primarily thyroxin) that
control metabolism
 Parathyroid glands
 Control levels of
calcium and
phosphate which in
turn controls levels of
excitability

 Pineal gland
 Secretes melatonin
which regulates the
sleep-wake cycle
 Pancreas
 Regulates blood-sugar
levels
 Secretes insulin and
glucagon

 Pituitary gland
 Referred to as the
“master gland”
because it regulates
many other glands
 Gonads
 Ovaries and testes
secrete estrogens and
androgens
 Adrenal glands
 Secretes hormones in
reaction to stress

Genes, Evolution, and
Behavior

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”

Behavior Genetics
 Study of behavior from a genetic
perspective
 Animal behavior genetic studies include:
 Strain studies
 Selection studies

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

Human Behavior Genetics
 Adoption studies
 Used to assess the influence of environment
 Molecular genetics
 Direct study of the genetic code

Evolutionary Psychology
 Natural selection
 “Survival of the fittest”
 Evolutionary psychology looks at the
adaptive or survival value of behaviors

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

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