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Chapter 2
Neural and Genetic Bases of Behavior
Overview of Nervous System
LO 2.1 What Are the Nervous System, Neurons, and Nerves?
 Nervous System: an extensive network
of specialized cells that carry
information to and from all parts of the
body
 Neuroscience: deals with the structure
and function of neurons, nerves, and
nervous tissue
– relationship to behavior and learning
An Overview of the Nervous
System
The Neuron
 Neurons are specialized cells in the
nervous system that send and receive
information throughout the body.
– Neurons are the nervous system’s
building blocks.
A Neuron
The nervous system contains 90 to 180 billion neurons (98.8
percent in the brain and 1.2 percent in the spinal cord).
Each neuron transmits information to about a thousand
other neurons; there are trillions of different neural
connections in the brain.
Structure of the Neuron
LO 2.1 What Are the Nervous System, Neurons, and Nerves?
 Parts of a Neuron
– dendrites: branch-like structures that
receive messages from other neurons
– soma: the cell body of the neuron,
responsible for maintaining the life of
the cell
– axon: long, tube-like structure that
carries the neural message to other
cells
Neuron
Structure of a Neuron
There are three basic types of
neurons:
 Sensory
neurons: send information
from sensory receptors to the brain
 Motor neurons: send commands
from the brain to glands, muscles,
and organs
 Interneurons: connect other
neurons to one another
Structure and Operation
of the Neuron
Action Potential
– A neuron’s electrochemical impulse results
from positively and negatively charged
ions.
– The tiny electrical charge from the
chemical balance of an inactive neuron is
known as the resting potential.

negative ions inside the axon attract
positive ions along the external cell
membrane wall.

This electrical disturbance is called the
action potential.
Neural
Communication
 Action Potential
– a neural impulse; a brief electrical charge
that travels down an axon
– generated by the movement of positively
charged atoms in and out of channels in
the axon’s membrane
 Threshold
– the level of stimulation required to trigger a
neural impulse
 Firing is all or none
Synapses: Points of Chemical
Transmission between Neurons
– Axon terminal buttons contain round
sacs called synaptic vesicles.
– When an action potential arrives, it
causes these vesicles to release
chemical messengers, called
neurotransmitters, which travel
across the synaptic cleft.
– These neurotransmitters fit into the
receiving dendrites’ receptor sites,
like keys fit into locks.
Synaptic Transmission
Synaptic Transmission—Reuptake
Synaptic Transmission— Enzyme
Deactivation
Synapses: Chemical Transmission between
Neurons
After locking into receptor sites, neurotransmitters
either excite or inhibit firing of the receiving
neuron.
Excitatory messages increase the probability of an
action potential.
Inhibitory messages reduce the likelihood of neural
firing.

Whether the neuron fires will depend on which type
of message is in greater abundance.
Synapses: Chemical Transmission
between Neurons
 After neurotransmitters deliver their
messages they are either:
– Repackaged into new synaptic
vesicles in a process known as
reuptake or
– Broken down by enzymes and
removed from the synaptic cleft in a
process called enzyme deactivation.
Chemical Neurotransmitters
About 75 neurotransmitters have been
identified, including:
Acetylcholine (ACh): involved in muscle
contraction, cognition, and memory formation
 Dopamine (DA): controls large muscle
movements; influences pleasure and
motivation
 Endorphins: important in the experience of
pleasure and control of pain
 Serotonin: involved in regulating emotional
states such as depression, sleep cycles and
dreaming, aggression, and appetite

Agonists and Antagonists
Neurotransmitter
molecule
Receptor site on
receiving neuron
Receiving cell
membrane
Agonist mimics
neurotransmitter
Antagonist
blocks
neurotransmitter
Neural and Hormonal Systems
 The nervous system is the body’s
primary information system and is
divided into two major portions:
– Central nervous system
– Peripheral nervous system
Neural and Hormonal
Systems
 Nerves
– neural “cables” containing many axons
– part of the peripheral nervous system
– connect the central nervous system
with muscles, glands, and sense
organs
Organization of the
Nervous System
Nervous
system
Central
(brain and
spinal cord)
Peripheral
Autonomic (controls
self-regulated action of
internal organs and glands)
Skeletal (controls
voluntary movements of
skeletal muscles)
Sympathetic
(arousing)
Parasympathetic
(calming)
Nervous System
 Central Nervous System (CNS)
–the brain and spinal cord
 Peripheral Nervous System (PNS)
–the sensory and motor neurons
that connect the central nervous
system (CNS) to the rest of the
body
The Peripheral Nervous System
 Peripheral nervous system: All the nerves located
outside the brain and spinal cord.
– Its function—to connect the brain and spinal
cord with the organs and tissues of the body.
– The peripheral nervous system is composed of
two major divisions:
The somatic/skeletal nervous system
 The autonomic nervous system
– Sympathetic nervous system
– Parasympathetic nervous system

Spinal Cord: Connects the Peripheral
Nervous System to the Brain
 Central nervous system (CNS): brain and spinal cord
– Spinal cord: slender, tube-shaped part of the (CNS)
that connects the brain to the body via the peripheral
nervous system
 The spinal cord transmits information from sensory
neurons to the brain, and from the brain to motor
neurons that initiate movement.
 The upper segments of the spinal cord control the
upper parts of the body, while the lower segments
control the lower body.
 The spinal cord also controls some automatic,
involuntary responses to sensory stimuli called
reflexes.
Reflex
 a simple, automatic, inborn response to a
sensory stimulus
Brain
Sensory neuron
(incoming information)
Muscle
Skin
receptors
Motor neuron
(outgoing
information)
Interneuron
Spinal cord
Neural and Hormonal
Systems
Nervous
system
Central
(brain and
spinal cord)
Peripheral
Autonomic (controls
self-regulated action of
internal organs and glands)
Skeletal (controls
voluntary movements of
skeletal muscles)
Sympathetic
(arousing)
Parasympathetic
(calming)
The Endocrine System Communicates
by Secreting Hormones
 The endocrine system is interconnected with—but not
part of—the nervous system.
– consists of a network of glands that make
and secrete hormones - chemical
messengers.
– The pituitary gland, in the base of the
brain, releases about 10 different
hormones and is controlled by the
hypothalamus.
– Other endocrine glands include the thyroid
gland, the adrenal glands, and the gonads.
The Brain
Technology to Study the Brain
 Electroencephalograph (EEG): records
“waves” of electrical activity in the brain using
metal electrodes
 Computerized axial tomograph (CAT):
thousands of X-ray photos of the brain are
combined to form a cross-sectional picture
 Magnetic resonance imaging (MRI):
produces three-dimensional images of the brain’s
soft tissues by detecting magnetic activity from
nuclear particles in brain molecules
Technology to Study the Brain
 Positron emission tomography (PET):
measures neural activity in different brain regions
over several minutes by monitoring sugar glucose
consumption
 Functional magnetic resonance imaging
(fMRI): measures neural activity in different brain
regions averaged over seconds by monitoring
blood oxygen levels
PET Scan
MRI Scan
Three Major Brain Regions
 Their names come from their physical
location in the human embryo.
– Hindbrain: Located above the spinal
cord,
– Midbrain: Located above the
hindbrain
– Forebrain: Located above the
Figure 2-6 Development of
the Brain
The Brainstem and
Thalamus
Three Major Brain Regions: Hindbrain
 Hindbrain consists of:
– Medulla: controls breathing, heart
rate, swallowing, digestion, and
posture
– Pons: associated with sleep and
arousal
– Cerebellum: regulates and
coordinates body movement and may
The Cerebellum
Midbrain
Reticular formation: regulates and
maintains consciousness
– plays an important role in
controlling arousal
Forebrain
Controls complex emotional reactions,
cognitive processes, and movement
patterns. Consists of:
– Thalamus: the brain’s sensory relay
station
– Hypothalamus: regulates eating, drinking,
sexual activity, emotion, and body
temperature
– Limbic system: influences fear,
aggression, and new memories
– Cerebral cortex: located on top of these
structures; the most complex part of the
Thalamus
 Brain’s Sensory Switchboard
 Directs incoming information from the
sensory systems (except smell) to the
appropriate location on the cortex.
Limbic System
 a doughnut-shaped system of neural structures at the
border of the brainstem and cerebral hemispheres
 associated with emotions such as fear and aggression
and drives such as those for food and sex
 includes the hypothalamus, hippocampus and amygdala
The Limbic System
Hypothalamus
 neural structure lying below (hypo) the
thalamus
 directs several maintenance activities
eating
drinking
body temperature
 helps govern the endocrine system via the
pituitary gland
 linked to emotion
Hippocampus
 Structure linked to the
processing/formation of new explicit
memories
 Manufactures new neurons
Limbic System
 Amygdala [ah-MIG-dah-la]
–two almond-shaped neural
clusters that are components
of the limbic system and are
linked to emotion, especially
rage and fear
The Limbic System
 Electrode implanted in reward center
Figure 2-7 Main Parts of
the Human Brain
Lobes of the Cerebral Cortex
 The cerebral cortex is divided into two
rounded halves, called the cerebral
hemispheres.
– These hemispheres are connected
together at the bottom by the corpus
callosum.
– Both hemispheres are divided into
four major sections called lobes:
The Cerebral
Cortex
Cortical Localization
 Frontal Lobes
–involved in speaking and
muscle movements and in
making plans and judgments
 Parietal Lobes
–include the sensory cortex
Cortical Localization
 Occipital Lobes
–include the visual areas, each of
which receives visual information
from the opposite visual field
 Temporal Lobes
–include the auditory areas, each
of which receives auditory
information primarily from the
The Cerebral Cortex
The Cerebral
Cortex
 Motor Cortex
–area at the rear of the frontal
lobes that controls voluntary
movements
 Sensory Cortex
–area at the front of the
parietal lobes that registers
and processes body
The Cerebral Cortex
 Functional MRI
scan of the
visual cortex
activated by
light shown in
the subject’s
eyes
Visual and Auditory Cortex
Association Areas
 Areas of the cerebral
cortex that are not
involved in primary
motor or sensory
functions
 Involved in higher
mental functions
such as learning,
remembering,
thinking, and
speaking
The Cerebral Cortex
 Aphasia
– impairment of language, usually
caused by left hemisphere damage
either to Broca’s area (impairing
speaking) or to Wernicke’s area
(impairing understanding)
 Broca’s Area
– an area of the frontal lobe that directs
the muscle movements involved in
speech
Specialization and Integration
Brain Structures
Brain activity when hearing, seeing and
speaking words
Right and Left Cerebral Hemispheres
Function Differently: Cortical Lateralization
 Right hemisphere: superior to the left hemisphere in visual
and spatial tasks, recognizing nonlinguistic sounds,
identifying faces, and perceiving and expressing emotions
 Left hemisphere: superior to the right hemisphere at
language, logic, and providing explanations for events
 Women may be more likely than men to use both
hemispheres for language (their brains are more
bilateralized).
Brain Reorganization
Corpus Callosum
Brain Reorganization
Plasticity
–the brain’s capacity for
modification as evident in
brain reorganization
following damage
(especially in children) and
in experiments on the
Brain Reorganization
 Corpus Callosum
– large bundle of neural fibers
connecting the two brain hemispheres
and carrying messages between the
hemispheres
 Split Brain
– a condition in which the two
hemispheres of the brain are isolated
by cutting the connecting fibers (mainly
those of the corpus callosum) between
Testing the Split Brain
The Brain Can Alter Its Neural
Connections
– Plasticity: the flexibility of the brain to alter its
neural connections following injury
– Hemispherectomy: a radical surgical procedure in
which one of the cerebral hemispheres is removed
to control life-threatening epileptic seizures. The
remaining healthy hemisphere takes over many of
the functions of the removed hemisphere.
– Plasticity is highest in childhood, but it also occurs
in older adults.
Collateral Growth
The Brain Is Protected from Toxins
by the Blood-Brain Barrier
 Blood-brain barrier: a semipermeable wall
of tiny blood vessels that prevent certain
chemicals in the bloodstream from reaching
the brain
– The blood-brain barrier:
- Protects the brain from many
“foreign substances” in the blood
that may injure the brain,
- Protects the brain from hormones
The Brain Is Protected from Toxins
by the Blood-Brain Barrier
 Beneficial
substances allowed to
enter the brain through the bloodbrain barrier are blood gases, such
as oxygen, and small nutritional
molecules.
 An important nutritional molecule
transported out of the bloodstream
in this way is glucose.
 Scientists have learned how to trick
The Blood-Brain Barrier