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Chapter 2
Behavioral
Neuroscience
Copyright 2003 Prentice Hall
2-1
The Evolutionary Perspective
• The evolutionary perspective stresses the role of
physiological structures and behaviors in an
organism's adaptation to the environment and
ultimate survival.
• Natural SelectionThe principle of natural
selection states that the most fit organisms
survive because they adapt best to the
environment and thus pass on their genes to
future generations.
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Biology and Behavior
• The term behavioral neuroscience
describes the work of scientists from
several disciplines who work to
understand how the nervous system is
related to behavior.
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The Nervous System
• We use the processes of sensing,
processing, and responding to interact
with the environment.
• The nervous system is divided into the
central nervous system (CNS-brain and
spinal cord) and the peripheral nervous
system (PNS-all parts of the nervous
system outside the CNS), coordinates
these three activities.
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The CNS
• The spinal cord is composed of sensory
(afferent or ascending) and motor (efferent
or descending) nerves.
• Interneurons may connect sensory and
motor neurons.
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CNS Nerves
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The PNS
• The PNS is composed of the somatic division
and the autonomic division.
• The somatic division consists of afferent
(sensory) nerves that run from the receptors to
the brain and efferent (motor) nerves that run to
the glands and muscles.
• The autonomic division consists of the
sympathetic division, which mobilizes the body's
resources, and the parasympathetic division
which returns the body to a normal state of
homeastasis.
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Divisions of the Nervous System
• Central Nervous
System
– Brain
– Spinal cord
• Peripheral Nervous
System
– Somatic
– Autonomic
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Neurons: The Basic Cells
• The cells that make up the nervous
system are called neurons.
• Neurons are composed of:
– dendrites that receive signals from adjacent
neurons
– a cell body or soma
– an axon that transmits signals
– terminal buttons that contain
neurotransmitters.
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Structure of a Neuron
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Neurotransmitters
• Neurotransmitters enable the signal from
one neuron to be relayed to other neurons
across the synapse, a small gap that
separates neurons.
• A myelin sheath covers the axons of some
neurons to increase the speed of
transmission of the neural signal.
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The Synapse
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Key Neurotransmitters
• Acetylcholine (ACh): excitatory or
inhibitory
• Dopamine: inhibitory or excitatory
• Serotonin: inhibitory or excitatory
• Endorphins: inhibitory
• Norepinephrine: Generally excitatory
• Gamma amino butryic acid (GABA):
inhibitory
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Neurotransmitters
• Among the key neurotransmitters, dopamine has
been implicated in the development of
Parkinson's disease (low levels) and certain
types of schizophrenia (high levels).
• Acetycholine seems to play a role in Alzheimer's
disease (low levels).
• Serotonin has been implicated In a variety of
disorders, including depression and obsessivecompulsive disorder.
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How Neurons Communicate
• Ions (electrically charged particles) are
found on the inside and outside of the
neuron's semipermeable cell membrane
• When a neuron is in a resting state, more
negative ions are on the inside of the cell
(measured at -70 mV) than on the out
side.
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How Neurons Communicate
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How Neurons Communicate
• Neurotransmitters stimulate the cell
membrane to allow ions to enter the
neuron resulting in
– depolarization (positive ions move inside the
neuron resulting in excitation) or
– hyperpolarization (additional negative ions
move inside resulting in in hibition).
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How Neurons Communicate
• If depolarization of the dendrite and soma
reaches the threshold level (-65 to -60
mV), the axon quickly reverses electrical
charge (to about +40 mV), and the signal
is transmitted to the next neuron.
• This reversal in electrical charge known as
the action potential.
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The Action Potential
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How Neurons Communicate
• Neurotransmitters must be removed from
the synapse be fore another signal can be
transmitted.
• Removal is accomplished either by
destroying the neurotransmitter
(breakdown) or by taking it back into the
terminal buttons (reuptake).
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Agonists and Antagonists
• Agonists are drugs that promote the action
of a neurotransmitter.
• Antagonists are drugs that oppose or
inhibit the action of a neurotransmitter.
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Agonists and Antagonists
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Agonists and Antagonists
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The Brain: A Closer Look
• Phrenology is a pseudoscience
popularized in the 1800s by Franz Joseph
Gall
• Gall believed we could determine a
person's skills and characteristics by
identifying bumps on the skull.
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The Brain: A Closer Look
• Early studies of brain functioning involved
stimulating or removing portions of the
cortex.
• The stereotaxic instrument allowed
examination of subcortical structures
without damaging the cortex.
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The Brain: A Closer Look
• The electroencephalograph (EEG) provides an
investigator with a chart of a person's brain
waves.
• lmages of the structures of the brain can be
produced by computerized techniques such as:
–
–
–
–
the PET (positron emission tomography),
the CT or CAT (computerized axial tomography),
the MRI (magnetic resonance imaging),
and the fMRl (functional magnetic resonance
imaging).
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The Brain
• The brain is divided
into the hindbrain, the
midbrain, and the
forebrain.
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The Hindbrain
• The oldest of the three main divisions of
the brain.
• Its major structures are the medulla, pons,
and cerebellum.
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The Midbrain
• A major division of the brain that contains
fibers known as the reticular formation.
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The Forebrain
• A major division of the brain that consists
of subcortical structures and the two
hemispheres of the cerebral cortex
• The hemispheres of the cerebral cortex
are joined by the corpus collosum
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The Corpus Callosum
• Millions of myelinated axons connecting the
brain’s hemispheres
• Provides a pathway for communication between
the hemispheres
• If surgically severed for treatment of epilepsy,
hemispheres cannot communicate directly
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The Cortex
• The cerebral cortex covers the forebrain
and is divided into four lobes:
– frontal,
– parietal,
– temporal,
– and occipital.
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Lobes of the Cerebral Cortex
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Subcortical Structures
• A group of subcortical structures involved
in emotion, memory, eating, drinking, and
sexual behavior are located beneath the
cortex.
• These structures include the limbic
system, thalamus, and hypothalamus.
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Limbic System
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More About the Brain
• The brain has been described as plastic,
which means it can change over time and
recover to some degree even from
removal of an entire hemisphere.
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Plasticity in Brain and Behavior
• Some rats are housed alone in empty cages
• Their littermate twins are group-housed in cages
with toys, which are changed frequently
• Richer environments led to heavier, thicker
brains, more synapses, and better learning
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More About the Brain
• Studying the human brain yields
information about aphasias (language
deficits) and apraxias (nonverbal deficits).
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Sperry’s Split-Brain Experiment
• Split-brain subjects could not name
objects shown only to the right hemisphere
• If asked to select these objects with their
left hand, they succeeded
• The right side of the brain doesn’t control
speech
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The Endocrine System
• The endocrine system affects behavior by
producing and secreting hormones, which
are chemicals that regulate body
functions.
• Among the major endocrine glands are the
pineal gland, hypothalamus pituitary gland,
the thyroid gland, the pancreas, the
gonads, and the adrenal glands.
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The Endocrine System
• Endocrine system:
– Ductless glands that
regulate growth,
reproduction,
metabolism, mood,
and some behavior
• Hormones:
– Chemical messengers
secreted into the
bloodstream
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