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Chapter 28
Nervous System
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Can an Injured Spinal Cord Be Fixed?
• Injuries to the spinal cord
–
Disrupt communication between the central
nervous system (brain and spinal cord) and the
rest of the body
Spinal
cord
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The late actor Christopher Reeve
–
Suffered a spinal cord injury during an
equestrian competition
–
Was an influential advocate for spinal cord
research
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
NERVOUS SYSTEM STRUCTURE AND FUNCTION
28.1 Nervous systems receive sensory input,
interpret it, and send out appropriate commands
• Nervous systems
– Are the most intricately organized dataprocessing systems on Earth
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The nervous system obtains and processes sensory
information
–
And sends commands to effector cells, such as
muscles, that carry out appropriate responses
Sensory input
Integration
Sensory receptor
Motor output
Brain and spinal cord
Effector cells
Figure 28.1A
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Peripheral nervous
system (PNS)
Central nervous
system (CNS)
• Sensory neurons
– Conduct signals from sensory receptors
to the central nervous system (CNS)
• The CNS
– Consists of the brain and spinal cord
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• Interneurons in the CNS
– Integrate information and send it to motor
neurons
• Motor neurons
– Convey signals to effector cells
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• Automatic responses called reflexes
–
Provide an example of nervous system function
1 Sensory
receptor
2 Sensory neuron
Brain
Ganglion
Motor
neuron
3
Spinal
cord
4
Quadriceps
muscles
Interneuron
CNS
Flexor
muscles
Figure 28.1B
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Nerve
PNS
• Located outside the CNS, the peripheral
nervous system (PNS)
– Consists of nerves (bundles of fibers of
sensory and motor neurons) and ganglia
(clusters of cell bodies of the neurons)
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28.2 Neurons are the functional units of nervous
systems
• Neurons
– Are cells specialized for carrying signals
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• A neuron consists of
– A cell body
– Two types of extensions (fibers) that conduct
signals, dendrites and axons
Signal direction Dendrites
SEM 3,600
Cell body
Cell body
Node of Ranvier
Layers of myelin
in sheath
Axon
Nucleus
Signal
pathway
Schwann cell
Nucleus
Nodes of
Ranvier
Figure 28.2
Myelin sheath
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Synaptic terminals
Schwann cell
• Many axons are enclosed by cellular insulation
called the myelin sheath
– Which speeds up signal transmission
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NERVE SIGNALS AND THEIR TRANSMISSION
28.3 A neuron maintains a membrane potential across its
membrane
• At rest, a neuron’s plasma membrane
–
Has an electrical voltage called the resting potential
Voltmeter
Plasma
membrane
Microelectrode
outside cell
– 70 mV
Microelectrode
inside cell
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Axon
Neuron
Figure 28.3A
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• The resting potential
–
Is caused by the membrane’s ability to maintain
a positive charge on its outer surface opposing
a negative charge on its inner surface
Outside of cell
Na+
Na+
K+
Na+
Na+
Na+
Na+
Na+
channel
Na+
Na+
K+
Plasma
membrane
K+
Na+
Na+
Na+
Na+
Na+
Na+ - K+
pump
K+ channel
Na+
K+
K+
K+
Protein
K+
K+
K+
K+
Figure 28.3B
Inside of cell
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Na+
K+
K+
28.4 A nerve signal begins as a change in the
membrane potential
• A stimulus alters the permeability of a portion of
the membrane
– Allowing ions to pass through and changing
the membrane’s voltage
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• A nerve signal, called an action potential
–
Is a change in the membrane voltage from
the resting potential to a maximum level and
back to the resting potential
Na+
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Na+
2 A stimulus opens some Na+
channels; if threshold is reached,
action potential is triggered.
Membrane potential
(mV)
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inactivate. K+ channels open,
and K+ rushes out; interior of
cell more negative than
outside.
+50
Na+
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K+
3 Additional Na+ channels open,
K+ channels are closed; interior
of cell becomes more positive.
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Action
potential
3
0
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– 50
Threshold
1
5 The K+ channels close
relatively slowly, causing
a brief undershoot.
1
5
– 100
Resting potential
Time (msec)
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Neuron
interior
1 Resting state: voltage-gated Na+
and K+ channels closed; resting
potential is maintained.
Figure 28.4
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Neuron
interior
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1 Return to resting state.
28.5 The action potential propagates itself along
the neuron
• Action potentials
– Are self-propagated in a one-way chain
reaction along a neuron
– Are all-or-none events
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• Propagation of the action potential along an axon
Axon
Action potential
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Figure 28.5
K+
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K
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Action potential

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+ Na +


Axon
segment
• The frequency of action potentials, but not their
strength
– Changes with the strength of the stimulus
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28.6 Neurons communicate at synapses
• The transmission of signals between neurons
– Or between neurons and effector cells
occurs at junctions called synapses
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• Electrical signals
– Pass between cells at electrical
synapses
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• At chemical synapses
– The sending cell secretes a chemical
signal, a neurotransmitter
• The neurotransmitter
– Crosses the synaptic cleft and binds to a
receptor on the surface of the receiving
cell
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• Neuron communication
Sending neuron
1
Action
potential
arrives
Vesicles
Axon of
sending
neuron
Synaptic
terminal
Synapse
2
Vesicle fuses
with plasma
membrane
3
Neurotransmitter
is released into
synaptic cleft
Receiving Synaptic
cleft
neuron
Receiving
neuron
Ion channels
Neurotransmitter
molecules
Neurotransmitter
Receptor
4
Neurotransmitter
binds to receptor
Neurotransmitter broken
down and released
Ions
5 Ion channel opens
Figure 28.6
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6 Ion channel closes
28.7 Chemical synapses make complex information
processing possible
• A neuron may receive information
–
From hundreds of other neurons via thousands of
synaptic terminals
Synaptic terminals
Dendrites
Myelin
sheath
Inhibitory Excitatory
Receiving
cell body
Axon
Figure 28.7
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SEM 5,500
Synaptic
terminals
• Some neurotransmitters
– Excite the receiving cell
• Other types of neurotransmitters
– Inhibit the receiving cell’s activity by
decreasing its ability to develop action
potentials
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• The summation of excitation and inhibition
– Determines whether or not a neuron will
transmit a nerve signal
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28.8 A variety of small molecules function as
neurotransmitters
• Many small, nitrogen-containing molecules
– Serve as neurotransmitters
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CONNECTION
28.9 Many drugs act at chemical synapses
• Many psychoactive drugs
–
Act at synapses and affect neurotransmitter
action
Figure 28.9
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AN OVERVIEW OF ANIMAL NERVOUS SYSTEMS
28.10 Nervous system organization usually correlates
with body symmetry
• Radially symmetrical animals
–
Have a nervous system arranged in a weblike
system of neurons called a nerve net
Nerve
net
Neuron
Figure 28.10A
A Hydra (cnidarian)
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• Most bilaterally symmetrical animals exhibit
–
Cephalization, the concentration of the
nervous system in the head region
–
Centralization, the presence of a central
nervous system
Eyespot
Brain
Brain
Brain
Nerve
cord
Tranverse
nerve
B Flatworm (planarian)
Ventral
nerve
cord
Ventral
nerve
cord
Brain
Giant
axon
Segmental
ganglion
C Leech (annelid)
Figure 28.10B–E
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Ganglia
D Insect (arthropod)
E Squid (mollusc)
28.11 Vertebrate nervous systems are highly
centralized and cephalized
Central nervous
system (CNS)
Brain
Spinal cord
Peripheral
nervous
system (PNS)
Cranial
nerves
Ganglia
outside CNS
Spinal
nerves
Figure 28.11A
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• The brain and spinal cord
– Contain fluid-filled spaces
Cerebrospinal fluid
Brain
Meninges
Gray matter
Dorsal root
ganglion
(part of PNS)
White matter
Central canal
Spinal nerve
(part of PNS)
Ventricles
Central canal
of spinal cord
Spinal cord
Figure 28.11B
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Spinal cord
(cross section)
• Cranial and spinal nerves
– Make up the peripheral nervous system
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28.12 The peripheral nervous system of vertebrates is a
functional hierarchy
• The PNS can be divided into two functional components
–
The somatic nervous system and the autonomic
nervous system
Peripheral
nervous system
Somatic
nervous
system
Autonomic
nervous
system
Sympathetic
division
Figure 28.12
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Parasympathetic
division
Enteric
division
• The somatic nervous system
– Carries signals to and from skeletal
muscles, mainly in response to external
stimuli
• The autonomic nervous system
– Regulates the internal environment by
controlling smooth and cardiac muscles
and the organs of various body systems
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28.13 Opposing actions of sympathetic and
parasympathetic neurons regulate the internal
environment
• The parasympathetic division of the autonomic
nervous system
–
Primes the body for activities that gain and
conserve energy for the body
• The sympathetic division of the autonomic nervous
system
–
Prepares the body for intense, energyconsuming activities
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• The autonomic nervous system
Parasympathetic division
Brain
Sympathetic division
Eye
Constricts
pupil
Dilates
pupil
Salivary
glands
Stimulates
saliva
production
Inhibits
saliva
production
Lung
Dilates
bronchi
Constricts
bronchi
Spinal
cord
Slows
heart
Heart
Liver
Stomach
Stimulates
stomach,
pancreas,
and intestines
Accelerates
Adrenal heart
gland
Stimulates
epinephrine
and norepinephrine release
Pancreas Stimulates
glucose release
Inhibits
stomach,
pancreas,
and intestines
Intestines
Bladder
Stimulates
urination
Inhibits
urination
Promotes
erection of
genitals
Promotes
ejaculation
and vaginal
contractions
Figure 28.13
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Genitalia
28.14 The vertebrate brain develops from three anterior
bulges of the neural tube
• The vertebrate brain
–
Develops from the forebrain, midbrain, and hindbrain
Embryonic
Brain Regions
Brain Structures
Present in Adult
Cerebrum (cerebral hemispheres; includes
cerebral cortex, white matter, basal ganglia)
Forebrain
Diencephalon (thalamus, hypothalamus,
posterior pituitary, pineal gland)
Midbrain
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Hindbrain
Medulla oblongata (part of brainstem)
Cerebral
hemisphere
Midbrain
Hindbrain
Diencephalon
Midbrain
Pons
Cerebellum
Medulla
oblongata
Spinal cord
Forebrain
Figure 28.14
Embryo (one month old)
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Fetus (three months old)
• The size and complexity of the cerebrum in
birds and mammals
– Correlates with their sophisticated
behavior
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THE HUMAN BRAIN
28.15 The structure of a living supercomputer:
The human brain
• The human brain
– Is more powerful than the most
sophisticated computer
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• The human brain is composed of three main parts
–
The forebrain, the midbrain, and the
hindbrain
Cerebral
cortex
Cerebrum
Forebrain
Thalamus
Hypothalamus
Pituitary gland
Midbrain
Pons
Hindbrain
Figure 28.15A
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Medulla
oblongata
Cerebellum
Spinal
cord
• Major structures of the human brain
Table 28.15
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• The midbrain and subdivisions of the hindbrain,
together with the thalamus and hypothalamus
– Function mainly in conducting
information to and from higher brain
centers
– Regulate homeostatic functions, keep
track of body position, and sort sensory
information
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• The forebrain’s cerebrum
– Is the largest and most complex part of
the brain
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• Most of the cerebrum’s integrative power
– Resides in the cerebral cortex of the two
cerebral hemispheres
Left cerebral
hemisphere
Figure 28.15B
Corpus
callosum
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Right cerebral
hemisphere
Basal
ganglia
28.16 The cerebral cortex is a mosaic of specialized,
interactive regions
• Specialized integrative regions of the cerebral cortex include
–
The somatosensory cortex and centers for vision,
hearing, taste, and smell
Frontal lobe
Parietal lobe
Frontal
association
area
Speech
Somatosensory
association
area
Taste
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Figure 28.16
Temporal lobe
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Occipital lobe
• The motor cortex
– Directs responses
• Association areas
– Concerned with higher mental activities
such as reasoning and language, make
up most of the cerebrum
• The right and left cerebral hemispheres
– Tend to specialize in different mental
tasks
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CONNECTION
28.17 Injuries and brain operations provide insight
into brain function
• Brain injuries and surgeries
–
Have been used to study brain function
Figure 28.17A, B
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28.18 Several parts of the brain regulate sleep
and arousal
• Sleep and arousal involve
– Activity by the hypothalamus, medulla
oblongata, pons, and neurons of the
reticular formation
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• The reticular formation
–
Receives data from sensory receptors and
sends useful data to the cerebral cortex
Data to cerebral cortex
Eye
Reticular formation
Figure 28.18A
Input from touch, pain,
and temperature receptors
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Input from
ears
• An EEG
– Measures brain waves during sleep and
arousal
Awake but quiet (alpha waves)
Awake during intense mental activity (beta waves)
Figure 28.18B, C
Delta waves
Asleep
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REM sleep
Delta waves
28.19 The limbic system is involved in emotions,
memory, and learning
• The limbic system
–
Is a functional group of integrating centers in the
cerebral cortex, thalamus, and hypothalamus
–
Is involved in emotions, memory, and learning
Thalamus
Hypothalamus
Cerebrum
Prefrontal
cortex
Smell
Figure 28.19
Olfactory
Amygdala
bulb
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Hippocampus
CONNECTION
20.20 Changes in brain physiology can produce
neurological disorders
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Schizophrenia
• Schizophrenia is a severe mental disturbance
– Characterized by psychotic episodes in
which patients lose the ability to
distinguish reality
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Depression
• Two broad forms of depressive illness have
been identified
– Major depression and bipolar disorder
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Selective serotonin reuptake inhibitors (SSRIs)
– Are prescribed to treat depression
140
Prescriptions (millions)
120
100
80
60
40
20
0
Figure 28.20A
1995
1996
1997
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1998
1999
Year
2000
2001 2002
2003
Alzheimer’s Disease
• Alzheimer’s disease (AD)
– Is characterized by confusion, memory
loss, and a variety of other symptoms
Figure 28.20B
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Neurofibrillary tangle
LM 250
Senile plaque
Parkinson’s Disease
• Parkinson’s disease is a motor disorder
–
Characterized by difficulty in initiating
movements, slowness of movement, and rigidity
Figure 28.20C
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings