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CAMPBELL
BIOLOGY
TENTH
EDITION
Reece • Urry • Cain • Wasserman • Minorsky • Jackson
49
Nervous Systems
Lecture Presentation by
Nicole Tunbridge and
Kathleen Fitzpatrick
© 2014 Pearson Education, Inc.
Command and Control Center
 The human brain contains about 100 billion
neurons, organized into circuits more complex
than the most powerful supercomputers
 Powerful imaging techniques allow researchers to
monitor multiple areas of the brain while the
subject performs various tasks
 A recent advance uses expression of
combinations of colored proteins in brain cells, a
technique called “brainbow”
© 2014 Pearson Education, Inc.
Figure 49.1
© 2014 Pearson Education, Inc.
Concept 49.1: Nervous systems consist of
circuits of neurons and supporting cells
 By the time of the Cambrian explosion more than
500 million years ago, specialized systems of
neurons had appeared that enables animals to
sense their environments and respond rapidly
© 2014 Pearson Education, Inc.
 The simplest animals with nervous systems, the
cnidarians, have neurons arranged in nerve nets
 A nerve net is a series of interconnected nerve
cells
 More complex animals have nerves, in which the
axons of multiple neurons are bundled together
 Nerves channel and organize information flow
through the nervous system
© 2014 Pearson Education, Inc.
Figure 49.2
Eyespot
Nerve net
(a) Hydra (cnidarian)
Brain
Brain
Nerve
cords
Radial
nerve
Nerve
ring
Ventral
nerve cord
Transverse
nerve
(b) Sea star (echinoderm)
Segmental
ganglia
(c) Planarian (flatworm)
(d) Leech (annelid)
Brain
Ganglia
Brain
Ventral
nerve
cord
Segmental
ganglia
(e) Insect (arthropod)
© 2014 Pearson Education, Inc.
Anterior
nerve ring
Brain
Ganglia
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
Longitudinal
nerve cords
(f) Chiton (mollusc)
(g) Squid (mollusc)
(h) Salamander
(vertebrate)
Figure 49.2a
Nerve net
(a) Hydra (cnidarian)
Radial
nerve
Nerve
ring
(b) Sea star (echinoderm)
Eyespot
Brain
Nerve
cords
Transverse
nerve
(c) Planarian (flatworm)
© 2014 Pearson Education, Inc.
Brain
Ventral
nerve cord
Segmental
ganglia
(d) Leech (annelid)
Figure 49.2a, b
Nerve net
(a) Hydra (cnidarian)
© 2014 Pearson Education, Inc.
Radial
nerve
Nerve
ring
(b) Sea star (echinoderm)
 Bilaterally symmetrical animals exhibit
cephalization, the clustering of sensory organs at
the front end of the body
 The simplest cephalized animals, flatworms, have
a central nervous system (CNS)
 The CNS consists of a brain and longitudinal
nerve cords
 The peripheral nervous system (PNS) consists
of neurons carrying information into and out of the
CNS
© 2014 Pearson Education, Inc.
Figure 49.2c
Eyespot
Brain
Nerve
cords
Transverse
nerve
(c) Planarian (flatworm)
© 2014 Pearson Education, Inc.
 Annelids and arthropods have segmentally
arranged clusters of neurons called ganglia
© 2014 Pearson Education, Inc.
Figure 49.2d, e
Brain
Ventral
nerve cord
Segmental
ganglia
(d) Leech (annelid)
© 2014 Pearson Education, Inc.
Brain
Ventral
nerve
cord
Segmental
ganglia
(e) Insect (arthropod)
Figure 49.2b
Ganglia
Brain
Ventral
nerve
cord
Segmental
ganglia
Anterior
nerve ring
Longitudinal
nerve cords
(e) Insect (arthropod)
(f) Chiton (mollusc)
Brain
Brain
Ganglia
(g) Squid (mollusc)
© 2014 Pearson Education, Inc.
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
(h) Salamander (vertebrate)
 Nervous system organization usually correlates
with lifestyle
 Sessile molluscs (for example, clams and chitons)
have simple systems, whereas more complex
molluscs (for example, octopuses and squids)
have more sophisticated systems
© 2014 Pearson Education, Inc.
Figure 49.2f, g
Ganglia
Anterior
nerve ring
Brain
Ganglia
Longitudinal
nerve cords
(f) Chiton (mollusc)
© 2014 Pearson Education, Inc.
(g) Squid (mollusc)
 In vertebrates
 The CNS is composed of the brain and spinal cord
 The peripheral nervous system (PNS) is composed
of nerves and ganglia
 Region specialization is a hallmark of both
systems
© 2014 Pearson Education, Inc.
Figure 49.2h
Brain
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
(h) Salamander (vertebrate)
© 2014 Pearson Education, Inc.
Glia
 Glial cells, or glia have numerous functions to
nourish, support, and regulate neurons
 Embryonic radial glia form tracks along which newly
formed neurons migrate
 Astrocytes induce cells lining capillaries in the
CNS to form tight junctions, resulting in a bloodbrain barrier and restricting the entry of most
substances into the brain
© 2014 Pearson Education, Inc.
Figure 49.3
Capillary
CNS
Neuron
PNS
VENTRICLE
Cilia
Ependymal
cells
© 2014 Pearson Education, Inc.
Astrocytes
Oligodendrocytes
Microglia
Schwann cells
 Radial glial cells and astrocytes can both act as
stem cells
 Researchers are trying to find a way to use neural
stem cells to replace brain tissue that has ceased
to function normally
© 2014 Pearson Education, Inc.
Figure 49.4
© 2014 Pearson Education, Inc.
Organization of the Vertebrate Nervous System
 The CNS develops from the hollow nerve cord
 The cavity of the nerve cord gives rise to the
narrow central canal of the spinal cord and the
ventricles of the brain
 The canal and ventricles fill with cerebrospinal
fluid, which supplies the CNS with nutrients and
hormones and carries away wastes
© 2014 Pearson Education, Inc.
Figure 49.5
Gray matter
White
matter
Ventricles
© 2014 Pearson Education, Inc.
 The brain and spinal cord contain
 Gray matter, which consists of neuron cell bodies,
dendrites, and unmyelinated axons
 White matter, which consists of bundles of
myelinated axons
© 2014 Pearson Education, Inc.
Figure 49.6
Central
nervous
system
(CNS)
Brain
Spinal
cord
Cranial nerves
Ganglia
outside CNS
Spinal nerves
© 2014 Pearson Education, Inc.
Peripheral
nervous
system
(PNS)
 The spinal cord conveys information to and from
the brain and generates basic patterns of
locomotion
 The spinal cord also produces reflexes
independently of the brain
 A reflex is the body’s automatic response to a
stimulus
 For example, a doctor uses a mallet to trigger a
knee-jerk reflex
© 2014 Pearson Education, Inc.
Figure 49.7
Cell body of
sensory neuron in
dorsal root ganglion
Gray
matter
Quadriceps
muscle
Spinal cord
(cross section)
Hamstring
muscle
Key
Sensory neuron
Motor neuron
Interneuron
© 2014 Pearson Education, Inc.
White
matter
The Peripheral Nervous System
 The PNS transmits information to and from the
CNS and regulates movement and the internal
environment
 In the PNS, afferent neurons transmit information
to the CNS and efferent neurons transmit
information away from the CNS
© 2014 Pearson Education, Inc.
Figure 49.8
CENTRAL NERVOUS
SYSTEM
(information processing)
PERIPHERAL NERVOUS
SYSTEM
Efferent neurons
Afferent neurons
Sensory
receptors
Autonomic
nervous system
Motor
system
Control of
skeletal muscle
Internal
and external
stimuli
Sympathetic Parasympathetic
division
division
Enteric
division
Control of smooth muscles,
cardiac muscles, glands
© 2014 Pearson Education, Inc.
 The PNS has two efferent components: the motor
system and the autonomic nervous system
 The motor system carries signals to skeletal
muscles and is voluntary
 The autonomic nervous system regulates
smooth and cardiac muscles and is generally
involuntary
© 2014 Pearson Education, Inc.
 The autonomic nervous system has sympathetic
and parasympathetic divisions
 The sympathetic division regulates arousal and
energy generation (“fight-or-flight” response)
 The parasympathetic division has antagonistic
effects on target organs and promotes calming
and a return to “rest and digest” functions
© 2014 Pearson Education, Inc.
Figure 49.9
Parasympathetic division
Sympathetic division
Constricts pupil of eye
Dilates pupil of eye
Stimulates salivary
gland secretion
Inhibits salivary
gland secretion
Constricts
bronchi in lungs
Cervical
Sympathetic
ganglia
Relaxes bronchi in lungs
Slows heart
Accelerates heart
Stimulates activity of
stomach and intestines
Inhibits activity of
stomach and intestines
Thoracic
Stimulates activity
of pancreas
Inhibits activity
of pancreas
Stimulates gallbladder
Stimulates glucose
release from liver;
inhibits gallbladder
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Promotes erection
of genitalia
© 2014 Pearson Education, Inc.
Inhibits emptying
of bladder
Sacral
Synapse
Promotes ejaculation and
vaginal contractions
Figure 49.9a
Parasympathetic division
Sympathetic division
Constricts pupil of eye
Dilates pupil
of eye
Stimulates salivary
gland secretion
Inhibits salivary
gland secretion
Constricts
bronchi in lungs
Slows heart
Stimulates activity of
stomach and intestines
Stimulates activity
of pancreas
Stimulates gallbladder
© 2014 Pearson Education, Inc.
Cervical
Sympathetic
ganglia
Figure 49.9b
Parasympathetic
division
Sympathetic division
Relaxes bronchi in lungs
Sympathetic
ganglia
Accelerates heart
Inhibits activity of
stomach and intestines
Thoracic
Inhibits activity
of pancreas
Stimulates glucose
release from liver;
inhibits gallbladder
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Promotes erection
of genitalia
© 2014 Pearson Education, Inc.
Inhibits emptying
of bladder
Sacral
Synapse
Promotes ejaculation and
vaginal contractions
Concept 49.2: The vertebrate brain is regionally
specialized
 Specific brain structures are particularly
specialized for diverse functions
 The vertebrate brain has three major regions: the
forebrain, midbrain, and hindbrain
© 2014 Pearson Education, Inc.
Figure 49.UN01
Forebrain
Midbrain
Hindbrain
Cerebellum
Olfactory
bulb
Cerebrum
© 2014 Pearson Education, Inc.
 The forebrain has activities including processing
of olfactory input, regulation of sleep, learning, and
any complex processing
 The midbrain coordinates routing of sensory input
 The hindbrain controls involuntary activities and
coordinates motor activities
© 2014 Pearson Education, Inc.
 Comparison of vertebrates shows that relative
sizes of particular brain regions vary
 These size differences reflect the relative
importance of the particular brain function
 Evolution has resulted in a close match between
structure and function
© 2014 Pearson Education, Inc.
Figure 49.10
Lamprey
ANCESTRAL
VERTEBRATE
Shark
Ray-finned
fish
Amphibian
Crocodilian
Key
Forebrain
Midbrain
Hindbrain
© 2014 Pearson Education, Inc.
Bird
Mammal
 During embryonic development the anterior neural
tube gives rise to the forebrain, midbrain, and
hindbrain
 The midbrain and part of the hindbrain form the
brainstem, which joins with the spinal cord at the
base of the brain
 The rest of the hindbrain gives rise to the cerebellum
 The forebrain divides into the diencephelon, which
forms endocrine tissues in the brain, and the
telencephalon, which becomes the cerebrum
© 2014 Pearson Education, Inc.
Figure 49.11a
© 2014 Pearson Education, Inc.
Figure 49.11b
Embryonic brain regions
Brain structures in child and adult
Telencephalon
Cerebrum (includes cerebral cortex, basal nuclei)
Diencephalon
Diencephalon (thalamus, hypothalamus, epithalamus)
Forebrain
Midbrain
Mesencephalon
Midbrain (part of brainstem)
Metencephalon
Pons (part of brainstem), cerebellum
Myelencephalon
Medulla oblongata (part of brainstem)
Hindbrain
Cerebrum
Mesencephalon
Metencephalon
Midbrain
Hindbrain
Diencephalon
Diencephalon
Myelencephalon
Forebrain
Embryo at 1 month
© 2014 Pearson Education, Inc.
Telencephalon
Cerebellum
Spinal
cord
Embryo at 5 weeks
Spinal cord
Child
Brainstem
Midbrain
Pons
Medulla
oblongata
Figure 49.11ba
Embryonic brain regions
Telencephalon
Forebrain
Diencephalon
Midbrain
Mesencephalon
Metencephalon
Hindbrain
Myelencephalon
Brain structures in child and adult
Cerebrum (includes cerebral cortex, basal nuclei)
Diencephalon (thalamus, hypothalamus, epithalamus)
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Medulla oblongata (part of brainstem)
© 2014 Pearson Education, Inc.
Figure 49.11bb
Mesencephalon
Metencephalon
Midbrain
Hindbrain
Forebrain
Embryo at 1 month
© 2014 Pearson Education, Inc.
Diencephalon
Myelencephalon
Telencephalon
Spinal
cord
Embryo at 5 weeks
Figure 49.11bc
Cerebrum
Diencephalon
Cerebellum
Spinal cord
Child
© 2014 Pearson Education, Inc.
Brainstem
Midbrain
Pons
Medulla
oblongata
Figure 49.11c
Left cerebral
hemisphere
Right cerebral
hemisphere
Cerebral cortex
Corpus callosum
Cerebrum
Basal nuclei
Cerebellum
Adult brain viewed from the rear
© 2014 Pearson Education, Inc.
Figure 49.11d
Diencephalon
Thalamus
Pineal gland
Hypothalamus
Pituitary gland
Midbrain
Pons
Medulla
oblongata
Spinal cord
© 2014 Pearson Education, Inc.
Arousal and Sleep
 The brainstem and cerebrum control arousal and
sleep
 The core of the brainstem has a diffuse network of
neurons called the reticular formation
 These neurons control the timing of sleep periods
characterized by rapid eye movements (REMs)
and by vivid dreams
 Sleep is also regulated by the biological clock and
regions of the forebrain that regulate intensity and
duration
© 2014 Pearson Education, Inc.
Figure 49.12
Eye
Reticular formation
Input from touch,
pain, and temperature
receptors
© 2014 Pearson Education, Inc.
Input from
nerves of
ears
 Sleep is essential and may play a role in the
consolidation of learning and memory
 Some animals have evolutionary adaptations
allowing for substantial activity during sleep
 Dolphins sleep with one brain hemisphere at a
time and are therefore able to swim while “asleep”
© 2014 Pearson Education, Inc.
Figure 49.13
Key
Low-frequency waves characteristic of sleep
High-frequency waves characteristic of wakefulness
Location
Left
hemisphere
Right
hemisphere
© 2014 Pearson Education, Inc.
Time: 0 hours
Time: 1 hour
Biological Clock Regulation
 Cycles of sleep and wakefulness are examples of
circadian rhythms, daily cycles of biological activity
 Such rhythms rely on a biological clock, a
molecular mechanism that directs periodic gene
expression and cellular activity
 Biological clocks are typically synchronized to light
and dark cycles
© 2014 Pearson Education, Inc.
 In mammals, circadian rhythms are coordinated by
a group of neurons in the hypothalamus called the
suprachiasmatic nucleus (SCN)
 The SCN acts as a pacemaker, synchronizing the
biological clock
© 2014 Pearson Education, Inc.
Emotions
 Generation and experience of emotions involve
many brain structures, including the amygdala,
hippocampus, and parts of the thalamus
 These structures are grouped as the limbic system
© 2014 Pearson Education, Inc.
Figure 49.14
Thalamus
Hypothalamus
Olfactory
bulb
Amygdala
© 2014 Pearson Education, Inc.
Hippocampus
 Generating and experiencing emotion often
require interactions between different parts of the
brain
 The structure most important to the storage of
emotion in the memory is the amygdala, a mass
of nuclei near the base of the cerebrum
© 2014 Pearson Education, Inc.
Functional Imaging of the Brain
 Brain structures are probed and analyzed with
functional imaging methods
 Positron-emission tomography (PET) enables a
display of metabolic activity through injection of
radioactive glucose
 Today, many studies rely on functional magnetic
resonance imaging (fMRI), in which brain activity
is detected through changes in local oxygen
concentration
© 2014 Pearson Education, Inc.
Figure 49.15
Nucleus accumbens
Happy music
© 2014 Pearson Education, Inc.
Amygdala
Sad music
Figure 49.15a
Nucleus accumbens
Happy music
© 2014 Pearson Education, Inc.
Figure 49.15b
Amygdala
Sad music
© 2014 Pearson Education, Inc.
 The range of applications for fMRI include
monitoring recovery from stroke, mapping
abnormalities in migraine headaches, and
increasing the effectiveness of brain surgery
© 2014 Pearson Education, Inc.
Concept 49.3: The cerebral cortex controls
voluntary movement and cognitive functions
 The cerebrum, the largest structure in the human
brain, is essential for language, cognition,
memory, consciousness, and awareness of our
surroundings
 Four regions, or lobes (frontal, temporal, occipital,
and parietal), are landmarks for particular
functions
© 2014 Pearson Education, Inc.
Figure 49.16
Motor cortex (control of
skeletal muscles)
Somatosensory
cortex
(sense of touch)
Sensory association
cortex (integration
of sensory information)
Frontal lobe
Parietal lobe
Prefrontal cortex
(decision making,
planning)
Visual
association
cortex (combining
images and object
recognition)
Broca’s area
(forming speech)
Temporal lobe
Occipital lobe
Auditory cortex
(hearing)
Cerebellum
Wernicke’s area
(comprehending
language)
© 2014 Pearson Education, Inc.
Visual cortex
(processing visual
stimuli and pattern
recognition)
Information Processing
 The cerebral cortex receives input from sensory
organs and somatosensory receptors
 Somatosensory receptors provide information
about touch, pain, pressure, temperature, and the
position of muscles and limbs
 The thalamus directs different types of input to
distinct locations
© 2014 Pearson Education, Inc.
 Information received at the primary sensory areas
is passed to nearby association areas that process
particular features of the input
 Integrated sensory information passes to the
prefrontal cortex, which helps plan actions and
movements
 In the somatosensory cortex and motor cortex,
neurons are arranged according to the part of the
body that generates input or receives commands
© 2014 Pearson Education, Inc.
Figure 49.17
Frontal lobe
Parietal lobe
Toes
Genitalia
Lips
Jaw
Tongue
© 2014 Pearson Education, Inc.
Primary
motor
cortex
Abdominal
organs
Primary
somatosensory
cortex
Language and Speech
 Studies of brain activity have mapped areas
responsible for language and speech
 Patients with damage in Broca’s area in the frontal
lobe can understand language but cannot speak
 Damage to Wernicke’s area causes patients to be
unable to understand language, though they can
still speak
© 2014 Pearson Education, Inc.
Figure 49.18
Max
Hearing
words
Seeing
words
Min
Speaking
words
© 2014 Pearson Education, Inc.
Generating
words
Lateralization of Cortical Function
 The two hemispheres make distinct contributions
to brain function
 The left hemisphere is more adept at language,
math, logic, and processing of serial sequences
 The right hemisphere is stronger at facial and
pattern recognition, spatial relations, and
nonverbal thinking
© 2014 Pearson Education, Inc.
 The differences in hemisphere function are called
lateralization
 The two hemispheres work together by
communicating through the fibers of the corpus
callosum
© 2014 Pearson Education, Inc.
Frontal Lobe Function
 Frontal lobe damage may impair decision making
and emotional responses but leave intellect and
memory intact
 The frontal lobes have a substantial effect on
“executive functions”
© 2014 Pearson Education, Inc.
Figure 49.UN03
© 2014 Pearson Education, Inc.
Evolution of Cognition in Vertebrates
 Previous ideas that a highly convoluted neocortex
is required for advanced cognition may be
incorrect
 The anatomical basis for sophisticated information
processing in birds (without a highly convoluted
neocortex) appears to be the clustering of nuclei in
the top or outer portion of the brain (pallium)
© 2014 Pearson Education, Inc.
Figure 49.19
Cerebrum
(including pallium)
Cerebellum
Thalamus
Midbrain
(a) Songbird brain
Cerebrum (including
cerebral cortex)
Thalamus
Midbrain
(b) Human brain
© 2014 Pearson Education, Inc.
Cerebellum
Concept 49.4: Changes in synaptic connections
underlie memory and learning
 Two processes dominate embryonic development
of the nervous system
 Neurons compete for growth-supporting factors in
order to survive
 Only half the synapses that form during embryo
development survive into adulthood
© 2014 Pearson Education, Inc.
Neuronal Plasticity
 Neuronal plasticity describes the ability of the
nervous system to be modified after birth
 Changes can strengthen or weaken signaling at a
synapse
 Autism, a developmental disorder, involves a
disruption in activity-dependent remodeling at
synapses
 Children affected with autism display impaired
communication and social interaction, as well as
stereotyped, repetitive behaviors
© 2014 Pearson Education, Inc.
Figure 49.20
N1
N1
N2
N2
(a) Connections between neurons are strengthened or
weakened in response to activity.
(b) If two synapses are often active at the same time,
the strength of the postsynaptic response may
increase at both synapses.
© 2014 Pearson Education, Inc.
Memory and Learning
 The formation of memories is an example of
neuronal plasticity
 Short-term memory is accessed via the
hippocampus
 The hippocampus also plays a role in forming
long-term memory, which is later stored in the
cerebral cortex
 Some consolidation of memory is thought to occur
during sleep
© 2014 Pearson Education, Inc.
Long-Term Potentiation
 In the vertebrate brain, a form of learning called
long-term potentiation (LTP) involves an
increase in the strength of synaptic transmission
 LTP involves glutamate receptors
 If the presynaptic and postsynaptic neurons are
stimulated at the same time, the set of receptors
present on the postsynaptic membranes changes
© 2014 Pearson Education, Inc.
Figure 49.21
PRESYNAPTIC
NEURON
Glutamate
NMDA receptor
(open)
POSTSYNAPTIC
NEURON
Ca2+
Na+
Mg2+
Stored
AMPA
receptor
1
NMDA
receptor
(closed)
(a) Synapse prior to long-term potentiation (LTP)
3
(b) Establishing LTP
3
1
2
Depolarization
(c) Synapse exhibiting LTP
© 2014 Pearson Education, Inc.
4 Action
potential
2
Figure 49.21a
PRESYNAPTIC
NEURON
Glutamate
NMDA receptor
(open)
POSTSYNAPTIC
NEURON
Ca2+
Na+
Mg2+
Stored
AMPA
receptor
NMDA
receptor
(closed)
(a) Synapse prior to long-term potentiation (LTP)
© 2014 Pearson Education, Inc.
Figure 49.21b
1
3
(b) Establishing LTP
© 2014 Pearson Education, Inc.
2
Figure 49.21c
3
1
2
Depolarization
(c) Synapse exhibiting LTP
© 2014 Pearson Education, Inc.
4
Action
potential
Concept 49.5: Many nervous system disorders
can be explained in molecular terms
 Disorders of the nervous system include
schizophrenia, depression, drug addiction,
Alzheimer’s disease, and Parkinson’s disease
 These are a major public health problem
 Genetic and environmental factors contribute to
diseases of the nervous system
 To distinguish between genetic and environmental
variables, scientists often carry out family studies
© 2014 Pearson Education, Inc.
Figure 49.22
40
Genes shared with relatives of
person with schizophrenia
12.5% (3rd-degree relative)
25% (2nd-degree relative)
50% (1st-degree relative)
100%
30
20
Relationship to person with schizophrenia
© 2014 Pearson Education, Inc.
Identical twin
Fraternal twin
Child
Full sibling
Parent
Half sibling
Grandchild
Nephew/niece
Individual,
general
population
0
Uncle/aunt
10
First cousin
Risk of developing schizophrenia (%)
50
Schizophrenia
 About 1% of the world’s population suffers from
schizophrenia
 Schizophrenia is characterized by hallucinations,
delusions, and other symptoms
 Evidence suggests that schizophrenia affects
neuronal pathways that use dopamine as a
neurotransmitter
© 2014 Pearson Education, Inc.
Depression
 Two broad forms of depressive illness are known
 In major depressive disorder, patients have a
persistent lack of interest or pleasure in most
activities
 Bipolar disorder is characterized by manic (highmood) and depressive (low-mood) phases
 Treatments for these types of depression include
drugs such as Prozac, which increase the activity
of biogenic amines in the brain
© 2014 Pearson Education, Inc.
The Brain’s Reward System and Drug Addiction
 The brain’s reward system rewards motivation with
pleasure
 Some drugs are addictive because they increase
activity of the brain’s reward system
 These drugs include cocaine, amphetamine,
heroin, alcohol, and tobacco
 Drug addiction is characterized by compulsive
consumption and an inability to control intake
© 2014 Pearson Education, Inc.
 Addictive drugs enhance the activity of the
dopamine pathway
 Drug addiction leads to long-lasting changes in the
reward circuitry that cause craving for the drug
 As researchers expand their understanding of the
brain’s reward system, there is hope that their
insights will lead to better prevention and
treatment of drug addiction
© 2014 Pearson Education, Inc.
Figure 49.23
Nicotine
stimulates
dopaminereleasing
VTA neuron.
Inhibitory neuron
Dopaminereleasing
VTA neuron
Opium and heroin
decrease activity
of inhibitory
neuron.
Cocaine and
amphetamines
block removal
of dopamine
from synaptic
cleft.
Cerebral
neuron of
reward
pathway
© 2014 Pearson Education, Inc.
Reward
system
response
Alzheimer’s Disease
 Alzheimer’s disease is a mental deterioration
characterized by confusion and memory loss
 Alzheimer’s disease is caused by the formation of
neurofibrillary tangles and amyloid plaques in the
brain
 There is no cure for this disease though some
drugs are effective at relieving symptoms
© 2014 Pearson Education, Inc.
Figure 49.24
Amyloid plaque
© 2014 Pearson Education, Inc.
Neurofibrillary tangle
20 µm
Parkinson’s Disease
 Parkinson’s disease is a motor disorder caused
by death of dopamine-secreting neurons in the
midbrain
 It is characterized by muscle tremors, flexed
posture, and a shuffling gait
 There is no cure, although drugs and various other
approaches are used to manage symptoms
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Figure 49.UN04
Dopa
decarboxylase
L-dopa
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Dopamine
Circadian cycle period (hours)
Figure 49.UN02
Wild-type hamster
𝜏 hamster
Wild-type hamster with
SCN from 𝜏 hamster
𝜏 hamster with SCN
from wild-type hamster
24
23
22
21
20
19
Before
procedures
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After surgery
and transplant
Figure 49.UN05
Brain
Nerve net
Hydra (cnidarian)
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Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
Salamander (vertebrate)
Figure 49.UN06
CNS
PNS
VENTRICLE
Ependymal
cell
Cilia
Astrocyte
Oligodendrocyte
Schwann
cells
Capillary
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Neuron
Microglial cell
Figure 49.UN07
Cerebrum
Forebrain
Thalamus
Hypothalamus
Pituitary gland
Midbrain
Pons
Hindbrain
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Medulla
oblongata
Cerebellum
Spinal
cord
Figure 49.UN08
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