Ch. 49: Nervous Systems
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Many animals have a complex nervous system that consists of
 The central nervous system (CNS): the brain and
the spinal cord
 The peripheral nervous system (PNS) consists of
neurons/ nerves and ganglia (clusters of neurons)
carrying information into and out of the CNS. The
neurons of the PNS, when bundled together, form
nerves
Brain
 Region
specialization
is a hallmark
of both
systems
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
(h) Salamander (vertebrate)
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Figure 49.6
Central
nervous
system
(CNS)
Brain
Spinal
cord
Cranial nerves
Ganglia
outside CNS
Spinal nerves
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Peripheral
nervous
system
(PNS)
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 blood-brain barrier
and restricting the entry of most substances into the
brain
 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
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• Information is transmitted from a presynaptic cell (a neuron) to a
postsynaptic cell (a neuron, muscle, or gland cell)
• Most neurons are nourished or insulated by cells called glia or glial
cells
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80 µm
Glia
Cell bodies of neurons
Figure 49.3
Capillary
CNS
Neuron
PNS
VENTRICLE
Cilia
Ependymal
cells
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Astrocytes
Oligodendrocytes
Microglia
Schwann cells
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
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Figure 49.5
 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
Gray matter
White
matter
Ventricles
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 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
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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
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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
 The PNS is further broken down into the motor
division which we have voluntary control over,
and the involuntary autonomic division, further
broken down into the antagonistic sympathetic and
parasympathetic divisions as well as the enteric
division.
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 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
 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
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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
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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
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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
 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
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Figure 49.10
Comparison of vertebrates shows that relative sizes of
particular brain regions vary
These size differences reflect the relative importance of the
particular brain function
Lamprey
ANCESTRAL
VERTEBRATE
Shark
Ray-finned
fish
Amphibian
Crocodilian
Key
Forebrain
Midbrain
Hindbrain
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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
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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
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Telencephalon
Cerebellum
Spinal
cord
Embryo at 5 weeks
Spinal cord
Child
Brainstem
Midbrain
Pons
Medulla
oblongata
Figure 49.UN07
Cerebrum
Forebrain
Thalamus
Hypothalamus
Pituitary gland
Midbrain
Pons
Hindbrain
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Medulla
oblongata
Cerebellum
Spinal
cord
Figure 49.11d
Diencephalon
Thalamus
Pineal gland
Hypothalamus
Pituitary gland
Midbrain
Pons
Medulla
oblongata
Spinal cord
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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
 Sleep is essential and may play a role in the
consolidation of learning and memory
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Figure 49.12
Eye
Reticular formation
Input from touch,
pain, and temperature
receptors
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Input from
nerves of
ears
Key
Some animals have evolutionary adaptations allowing for
substantial activity during sleep
Dolphins, for example, sleep with one brain hemisphere
at a time and are therefore able to swim while “asleep”
Low-frequency waves characteristic of sleep
High-frequency waves characteristic of wakefulness
Location
Left
hemisphere
Right
hemisphere
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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
 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
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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
 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
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Figure 49.14
Thalamus
Hypothalamus
Olfactory
bulb
Amygdala
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Hippocampus
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
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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)
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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
 Information received at the primary sensory areas
is passed to nearby association areas that process
particular features of the input
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Figure 49.17
Frontal lobe
Parietal lobe
Toes
Genitalia
Lips
Jaw
Tongue
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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
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Figure 49.18
Max
Hearing
words
Seeing
words
Min
Speaking
words
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Generating
words
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”
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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
 The differences in hemisphere function are called
lateralization
 The two hemispheres work together by communicating
through the fibers of the corpus callosum
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Memory and Learning
 Neuronal plasticity describes the ability of the
nervous system to be modified after birth
 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 longterm memory, which is later stored in the cerebral
cortex
 Some consolidation of memory is thought to occur
during sleep
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Figure 49.20
N1
N1
Study
hard…..
study
often….
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.
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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
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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
 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 (high-mood)
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
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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
 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
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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
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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
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 49.24
Amyloid plaque
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Neurofibrillary tangle
20 µm
Figure 49.11a
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