Download Nervous Systems Chapter 48 PowerPoint Lectures for Biology, Seventh Edition

Chapter 48
Nervous Systems
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Command and Control Center
• The human brain contains about 100 billion nerve
cells, or neurons
• Each neuron may communicate with thousands of
other neurons
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• Functional magnetic resonance imaging is a
technology that can reconstruct a threedimensional map of brain activity
• Brain imaging and other methods reveal that
groups of neurons function in specialized circuits
dedicated to different tasks
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 48.1: Nervous systems consist of circuits
of neurons and supporting cells
• All animals except sponges have a nervous
system
• What distinguishes nervous systems of different
animal groups is how neurons are organized into
circuits
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Organization of Nervous Systems
• The simplest animals with nervous systems, the
cnidarians, have neurons arranged in nerve nets
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LE 48-2a
Radial
nerve
Nerve net
Hydra (cnidarian)
Nerve
ring
Sea star (echinoderm)
• Sea stars have a nerve net in each arm connected
by radial nerves to a central nerve ring
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LE 48-2b
Eyespot
Brain
Brain
Nerve
cord
Transverse
nerve
Planarian (flatworm)
Ventral
nerve cord
Segmental
ganglion
Leech (annelid)
• Relatively simple cephalized animals, such as
flatworms, have a central nervous system (CNS)
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LE 48-2c
Ganglia
Brain
Ventral
nerve cord
Segmental
ganglia
Insect (arthropod)
Anterior
nerve ring
Longitudinal
nerve cords
Chiton (mollusc)
• Annelids and arthropods have segmentally
arranged clusters of neurons called ganglia
• These ganglia connect to the CNS and make up a
peripheral nervous system (PNS)
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LE 48-2d
Brain
Brain
Ganglia
Squid (mollusc)
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglion
Salamander (chordate)
• Nervous systems in molluscs correlate with
lifestyles
• Sessile molluscs have simple systems, whereas
more complex molluscs have more sophisticated
systems
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• In vertebrates, the central nervous system
consists of a brain and dorsal spinal cord
• The PNS connects to the CNS
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Information Processing
• Nervous systems process information in three
stages: sensory input, integration, and motor
output
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LE 48-3
Sensory input
Sensor
Integration
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
• Sensory neurons transmit information from
sensors that detect external stimuli and internal
conditions
• Sensory information is sent to the CNS, where
interneurons integrate the information
• Motor output leaves the CNS via motor neurons,
which communicate with effector cells
• The three stages of information processing are
illustrated in the knee-jerk reflex
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LE 48-4
Quadriceps
muscle
Cell body of
sensory neuron in
dorsal root
ganglion
Gray
matter
White
matter
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron
Neuron Structure
• Most of a neuron’s organelles are in the cell body
• Most neurons have dendrites, highly branched
extensions that receive signals from other neurons
• The axon is typically a much longer extension that
transmits signals to other cells at synapses
• Many axons are covered with a myelin sheath
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LE 48-5
Dendrites
Cell body
Nucleus
Axon hillock Axon
Presynaptic cell
Signal
direction
Synaptic
Myelin sheath terminals
Synapse
Postsynaptic cell
• Neurons have a wide variety of shapes that reflect
input and output interactions
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LE 48-6
Dendrites
Axon
Cell
body
Sensory neuron
Interneurons
Motor neuron
Supporting Cells (Glia)
• Glia are essential for structural integrity of the
nervous system and for functioning of neurons
• Types of glia: astrocytes, radial glia,
oligodendrocytes, and Schwann cells
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• In the CNS, astrocytes provide structural support
for neurons and regulate extracellular
concentrations of ions and neurotransmitters
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50 µm
LE 48-7
• Oligodendrocytes (in the CNS) and Schwann cells
(in the PNS) form the myelin sheaths around
axons of many vertebrate neurons
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LE 48-8
Nodes of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Myelin sheath
Nodes of
Ranvier
Schwann
cell
Nucleus of
Schwann cell
0.1 µm
Concept 48.2: Ion pumps and ion channels
maintain the resting potential of a neuron
• Across its plasma membrane, every cell has a
voltage called a membrane potential
• The cell’s inside is negative relative to the outside
• Membrane potential of a cell can be measured
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LE 48-9
Microelectrode
–70 mV
Voltage
recorder
Reference
electrode
The Resting Potential
• Resting potential is the membrane potential of a
neuron that is not transmitting signals
• Resting potential depends on ionic gradients
across the plasma membrane
Animation: Resting Potential
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• Concentration of Na+ is higher in the extracellular
fluid than in the cytosol
• The opposite is true for K+
• By modeling a neuron with an artificial membrane,
we can better understand resting potential
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LE 48-10
CYTOSOL
EXTRACELLULAR
FLUID
[Na+]
15 mM
[Na+]
150 mM
[K+]
150 mM
[K+]
5 mM
[Cl–]
[Cl–]
120 mM
10 mM
[A–]
100 mM
Plasma
membrane
LE 48-11
Inner
chamber
–92 mV
Outer
chamber
150 mM
KCl
Inner
chamber
15 mM
NaCl
5 mM
KCl
+62 mV
Outer
chamber
150 mM
NaCl
Cl–
K+
Potassium
channel
Cl–
Na+
Sodium
channel
Artificial
membrane
Membrane selectively permeable to K+
Membrane selectively permeable to Na+
• A neuron that is not transmitting signals contains
many open K+ channels and fewer open Na+
channels in its plasma membrane
• Diffusion of K+ and Na+ leads to a separation of
charges across the membrane, producing the
resting potential
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Gated Ion Channels
• Gated ion channels open or close in response to
one of three stimuli:
– Stretch-gated ion channels open when the
membrane is mechanically deformed
– Ligand-gated ion channels open or close when
a specific chemical binds to the channel
– Voltage-gated ion channels respond to a
change in membrane potential
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Concept 48.3: Action potentials are the signals
conducted by axons
• If a cell has gated ion channels, its membrane
potential may change in response to stimuli that
open or close those channels
• Some stimuli trigger a hyperpolarization, an
increase in magnitude of the membrane potential
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LE 48-12
Stimuli
Stimuli
+50
–50 Threshold
Resting
potential
Hyperpolarizations
0 1 2 3 4 5
Time (msec)
Graded potential hyperpolarizations
+50
Membrane potential (mV)
0
Membrane potential (mV)
Membrane potential (mV)
+50
–100
Stronger depolarizing stimulus
0
–50 Threshold
Resting
potential
–100
0
–50 Threshold
Resting
potential
Depolarizations
0 1 2 3 4 5
Time (msec)
Graded potential depolarizations
Action
potential
–100
0 1 2 3 4 5 6
Time (msec)
Action potential
• Other stimuli trigger a depolarization, a reduction
in the magnitude of the membrane potential
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• Hyperpolarization and depolarization are called
graded potentials
• The magnitude of the change in membrane
potential varies with the strength of the stimulus
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Production of Action Potentials
• Depolarizations are usually graded only up to a
certain membrane voltage, called the threshold
• A stimulus strong enough to produce
depolarization that reaches the threshold triggers
a response called an action potential
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• An action potential is a brief all-or-none
depolarization of a neuron’s plasma membrane
• It carries information along axons
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• Voltage-gated Na+ and K+ channels are involved
in producing an action potential
• When a stimulus depolarizes the membrane, Na+
channels open, allowing Na+ to diffuse into the cell
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• As the action potential subsides, K+ channels
open, and K+ flows out of the cell
• During the refractory period after an action
potential, a second action potential cannot be
initiated
Animation: Action Potential
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-13_5
Na+
Na+
Na+
Na+
K+
K+
Rising phase of the action potential
Falling phase of the action potential
Na+
Na+
Membrane potential
(mV)
+50
0
–50
K+
Action
potential
–100
Threshold
Resting potential
Time
Depolarization
Na+
Na+
Extracellular fluid
Na+
Potassium
channel
Activation
gates
K+
Plasma membrane
Cytosol
Resting state
Undershoot
Sodium
channel
K+
Inactivation
gate
Conduction of Action Potentials
• An action potential can travel long distances by
regenerating itself along the axon
• At the site where the action potential is generated,
usually the axon hillock, an electrical current
depolarizes the neighboring region of the axon
membrane
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LE 48-14c
Axon
Action
potential
Na+
An action potential is generated as Na+ flows inward
across the membrane at one location.
K+
Action
potential
Na+
K+
The depolarization of the action potential spreads to the
neighboring region of the membrane, re-initiating the
action potential there. To the left of this region, the
membrane is repolarizing as K+ flows outward.
K+
Action
potential
Na+
K+
The depolarization-repolarization process is repeated in the
next region of the membrane. In this way, local currents of
ions across the plasma membrane cause the action
potential to be propagated along the length of the axon.
Conduction Speed
• The speed of an action potential increases with
the axon’s diameter
• In vertebrates, axons are myelinated, also causing
an action potential’s speed to increase
• Action potentials in myelinated axons jump
between the nodes of Ranvier in a process called
saltatory conduction
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LE 48-15
Schwann cell
Depolarized region
(node of Ranvier)
Cell body
Myelin
sheath
Axon
Concept 48.4: Neurons communicate with other
cells at synapses
• In an electrical synapse, current flows directly from
one cell to another via a gap junction
• The vast majority of synapses are chemical
synapses
• In a chemical synapse, a presynaptic neuron
releases chemical neurotransmitters stored in the
synaptic terminal
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LE 48-16
Synaptic
terminals
of presynaptic
neurons
5 µm
Postsynaptic
neuron
• When an action potential reaches a terminal, the
final result is release of neurotransmitters into the
synaptic cleft
Animation: Synapse
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LE 48-17
Presynaptic
cell
Postsynaptic cell
Synaptic vesicles
containing
neurotransmitter
Na+
K+
Presynaptic
membrane
Neurotransmitter
Postsynaptic
membrane
Ligandgated
ion channel
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
Ca2+
Synaptic cleft
Ligand-gated
ion channels
Direct Synaptic Transmission
• Direct synaptic transmission involves binding of
neurotransmitters to ligand-gated ion channels
• Neurotransmitter binding causes ion channels to
open, generating a postsynaptic potential
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• Postsynaptic potentials fall into two categories:
– Excitatory postsynaptic potentials (EPSPs)
– Inhibitory postsynaptic potentials (IPSPs)
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• After release, the neurotransmitter diffuses out of
the synaptic cleft
• It may be taken up by surrounding cells and
degraded by enzymes
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Summation of Postsynaptic Potentials
• Unlike action potentials, postsynaptic potentials
are graded and do not regenerate
• Most neurons have many synapses on their
dendrites and cell body
• A single EPSP is usually too small to trigger an
action potential in a postsynaptic neuron
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LE 48-18
Terminal branch
of presynaptic
neuron
Postsynaptic E1
neuron
E1
E2
E1
E1
I
Membrane potential (mV)
Axon
hillock
0
Action
potential
Action
potential
Threshold of axon of
postsynaptic neuron
Resting
potential
–70
E1
E1
Subthreshold, no
summation
E1
E1
Temporal summation
E1 + E2
Spatial summation
E1
I
E1 + I
Spatial summation
of EPSP and IPSP
• If two EPSPs are produced in rapid succession, an
effect called temporal summation occurs
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• In spatial summation, EPSPs produced nearly
simultaneously by different synapses on the same
postsynaptic neuron add together
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• Through summation, an IPSP can counter the
effect of an EPSP
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Indirect Synaptic Transmission
• In indirect synaptic transmission, a
neurotransmitter binds to a receptor that is not
part of an ion channel
• This binding activates a signal transduction
pathway involving a second messenger in the
postsynaptic cell
• Effects of indirect synaptic transmission have a
slower onset but last longer
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Neurotransmitters
• The same neurotransmitter can produce different
effects in different types of cells
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Acetylcholine
• Acetylcholine is a common neurotransmitter in
vertebrates and invertebrates
• It can be inhibitory or excitatory
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Biogenic Amines
• Biogenic amines include epinephrine,
norepinephrine, dopamine, and serotonin
• They are active in the CNS and PNS
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Amino Acids and Peptides
• Four amino acids are known to function as
neurotransmitters in the CNS
• Several neuropeptides, relatively short chains of
amino acids, also function as neurotransmitters
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Gases
• Gases such as nitric oxide and carbon monoxide
are local regulators in the PNS
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Concept 48.5: The vertebrate nervous system is
regionally specialized
• Vertebrate nervous systems show a high degree
of cephalization and distinct CNS and PNS
components
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LE 48-19
Central nervous
system (CNS)
Peripheral nervous
system (PNS)
Brain
Spinal cord
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
• The brain provides the integrative power that
underlies the complex behavior of vertebrates
• The spinal cord integrates simple responses to
certain kinds of stimuli and conveys information to
and from the brain
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• The central canal of the spinal cord and the four
ventricles of the brain are hollow because they are
derived from the dorsal embryonic nerve cord
• Axons within the CNS are often found in bundles
that have a whitish appearance
• This white matter is distinguishable from gray
matter, which consists mainly of dendrites,
unmyelinated axons, and neuron cell bodies
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LE 48-20
Gray matter
White
matter
Ventricles
The Peripheral Nervous System
• The PNS transmits information to and from the
CNS and regulates movement and internal
environment
• Cranial nerves originate in the brain and terminate
mostly in organs of the head and upper body
• Spinal nerves originate in the spinal cord and
extend to parts of the body below the head
• The PNS has two functional components: the
somatic and autonomic nervous systems
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LE 48-21
Peripheral
nervous system
Somatic
nervous
system
Autonomic
nervous
system
Sympathetic
division
Parasympathetic
division
Enteric
division
• The somatic nervous system carries signals to
skeletal muscles
• The autonomic nervous system regulates the
internal environment, in an involuntary manner
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• The autonomic nervous system has sympathetic,
parasympathetic, and enteric divisions
• The sympathetic and parasympathetic divisions
have antagonistic effects on target organs
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• The sympathetic division correlates with the “fightor-flight” response
• The parasympathetic division promotes a return to
self-maintenance functions
• The enteric division controls activity of the
digestive tract, pancreas, and gallbladder
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LE 48-22
Sympathetic division
Parasympathetic division
Action on target organs:
Location of
preganglionic neurons:
brainstem and sacral
segments of spinal cord
Neurotransmitter
released by
preganglionic neurons:
acetylcholine
Location of
postganglionic neurons:
in ganglia close to or
within target organs
Action on target organs:
Dilates pupil
of eye
Constricts pupil
of eye
Inhibits salivary
gland secretion
Stimulates salivary
gland secretion
Constricts
bronchi in lungs
Cervical
Sympathetic
ganglia
Accelerates heart
Slows heart
Stimulates activity
of stomach and
intestines
Inhibits activity of
stomach and intestines
Thoracic
Inhibits activity
of pancreas
Stimulates activity
of pancreas
Stimulates
gallbladder
Stimulates glucose
release from liver;
inhibits gallbladder
Neurotransmitter
released by
preganglionic neurons:
acetylcholine
Location of
postganglionic neurons:
some in ganglia close to
target organs; others in
a chain of ganglia near
spinal cord
Lumbar
Neurotransmitter
released by
postganglionic neurons:
Promotes emptying
acetylcholine
of bladder
Promotes erection
of genitalia
Relaxes bronchi
in lungs
Location of
preganglionic neurons:
thoracic and lumbar
segments of spinal cord
Stimulates
adrenal medulla
Inhibits emptying
of bladder
Sacral
Synapse
Promotes ejaculation and
vaginal contractions
Neurotransmitter
released by
postganglionic neurons:
norepinephrine
Embryonic Development of the Brain
• All vertebrate brains develop from three embryonic
regions: forebrain, midbrain, and hindbrain
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LE 48-23
Brain structures present in adult
Embryonic brain regions
Telencephalon
Cerebrum (cerebral hemispheres; includes cerebral
cortex, white matter, 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
Mesencephalon
Metencephalon
Cerebral hemisphere
Diencephalon:
Hypothalamus
Thalamus
Midbrain
Hindbrain
Diencephalon
Myelencephalon
Pineal gland
(part of epithalamus)
Brainstem:
Midbrain
Pons
Spinal cord
Forebrain
Telencephalon
Pituitary
gland
Medulla
oblongata
Spinal cord
Cerebellum
Central canal
Embryo at one month
Embryo at five weeks
Adult
• By the fifth week of human embryonic
development, five brain regions have formed from
the three embryonic regions
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• As a human brain develops further, the most
profound change occurs in the forebrain, which
gives rise to the cerebrum
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The Brainstem
• The brainstem has three parts: the medulla
oblongata, the pons, and the midbrain
• The medulla oblongata contains centers that
control several visceral functions
• The pons also participates in visceral functions
• The midbrain contains centers for receipt and
integration of sensory information
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Arousal and Sleep
• The core of the brainstem has a diffuse network of
neurons called the reticular formation
• Part of this formation, called the reticular activating
system (RAS), regulates sleep and arousal
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LE 48-24
Eye
Input
from ears
Reticular formation
Input from touch,
pain, and temperature
receptors
The Cerebellum
• The cerebellum is important for coordination and
error checking during motor, perceptual, and
cognitive functions
• It is also involved in learning and remembering
motor skills
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Diencephalon
• The diencephalon develops into three regions: the
epithalamus, thalamus, and hypothalamus
• The epithalamus includes the pineal gland and
choroid plexus
• The thalamus is the main input center for sensory
information to the cerebrum and the main output
center for motor information leaving the cerebrum
• The hypothalamus regulates homeostasis and
basic survival behaviors such as feeding, fighting,
fleeing, and reproducing
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Circadian Rhythms
• The hypothalamus also regulates circadian
rhythms such as the sleep/wake cycle
• Animals usually have a biological clock, a pair of
suprachiasmatic nuclei (SCN) in the hypothalamus
• Biological clocks usually require external cues to
remain synchronized with environmental cycles
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LE 48-25
12 hr light–12 hr dark cycle
Light
Dark
Constant darkness
Light
Dark
1
Days of experiment
5
10
15
20
12
16
24
4
20
Time of day (hr)
8
12
12
16
24
4
20
Time of day (hr)
8
12
The Cerebrum
• The cerebrum develops from the embryonic
telencephalon
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The cerebrum has right and left hemispheres
• Each cerebral hemisphere consists of a cerebral
cortex overlying white matter and basal nuclei
• A thick band of axons called the corpus callosum
provides communication between the right and left
cerebral cortices
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• The basal nuclei are important centers for
planning and learning movement sequences
• In mammals, the cerebral cortex has a convoluted
surface called the neocortex
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LE 48-26
Left cerebral
hemisphere
Right cerebral
hemisphere
Corpus
callosum
Basal
nuclei
Neocortex
• In humans, the cerebral cortex is the largest and
most complex part of the brain
• Here sensory information is analyzed, motor
commands are issued, and language is generated
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Concept 48.6: The cerebral cortex controls
voluntary movement and cognitive functions
• Each side of the cerebral cortex has four lobes:
frontal, parietal, temporal, and occipital
• Each lobe contains primary sensory areas and
association areas
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LE 48-27
Frontal lobe
Parietal lobe
Speech
Frontal
association
area
Taste
Somatosensory
association
area
Reading
Speech
Hearing
Smell
Temporal lobe
Auditory
association
area
Visual
association
area
Vision
Occipital lobe
Information Processing in the Cerebral Cortex
• Specific types of sensory input enter the primary
sensory areas
• Adjacent areas process features in the sensory
input and integrate information from different
sensory areas
• In the somatosensory and motor cortices, neurons
are distributed according to the body part that
generates sensory input or receives motor input
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LE 48-28
Frontal lobe
Parietal lobe
Toes
Genitalia
Lips
Jaw
Tongue
Pharynx
Primary
motor cortex
Abdominal
organs
Primary
somatosensory
cortex
Lateralization of Cortical Function
• During brain development, competing functions
segregate and displace each other in the cortex of
the left and right cerebral hemispheres
• This process results in lateralization of functions
• The left hemisphere is more adept at language,
math, logic, and processing of serial sequences
• The right hemisphere is stronger at pattern
recognition, nonverbal thinking, and emotional
processing
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Language and Speech
• Studies of brain activity have mapped areas
responsible for language and speech
• Portions of the frontal lobe, Broca’s area and
Wernicke’s area, are essential for the generation
and understanding of language
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LE 48-29
Max
Hearing
words
Seeing
words
Min
Speaking
words
Generating
words
Emotions
• The limbic system is a ring of structures around
the brainstem
• It includes three parts of the cerebral cortex: the
amygdala, hippocampus, and olfactory bulb
• These structures interact with the neocortex to
mediate primary emotions and attach emotional
“feelings” to survival-related functions
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LE 48-30
Thalamus
Hypothalamus
Prefrontal
cortex
Olfactory
bulb
Amygdala
Hippocampus
• Structures of the limbic system form in early
development and provide a foundation for
emotional memory, associating emotions with
particular events or experiences
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Memory and Learning
• The frontal lobes are a site of short-term memory
• They interact with the hippocampus and amygdala
to consolidate long-term memory
• Many sensory and motor association areas of the
cerebral cortex are involved in storing and
retrieving words and images
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Cellular Mechanisms of Learning
• Experiments on invertebrates have revealed the
cellular basis of some types of learning
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LE 48-31a
Siphon
Mantle
Gill
Tail
Head
LE 48-31b
Gill withdrawal pathway
Touching
the siphon
Siphon
sensory neuron
Gill motor
neuron
Gill
Sensitization
pathway
Shocking
the tail
Interneuron
Tail sensory
neuron
• In the vertebrate brain, a form of learning called
long-term potentiation (LTP) involves an increase
in the strength of synaptic transmission
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-32
PRESYNAPTIC NEURON
NO
NMDA
receptor
Glutamate
AMPA receptor
NO
P
Ca2+
Signal transduction pathways
POSTSYNAPTIC NEURON
Consciousness
• Modern brain-imaging techniques suggest that
consciousness is an emergent property of the
brain based on activity in many areas of the cortex
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 48.7: CNS injuries and diseases are the
focus of much research
• Unlike the PNS, the mammalian CNS cannot
repair itself when damaged by disease
• Current research on nerve cell development and
stem cells may one day make it possible to repair
or replace damaged neurons
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Nerve Cell Development
• Signal molecules direct an axon’s growth by
binding to receptors on the plasma membrane of
the growth cone
• This receptor binding triggers a signal transduction
pathway, which may cause an axon to grow
toward or away from the signal source
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-33a
Midline of
spinal cord
Developing axon
of interneuron
Growth
cone
Netrin-1
receptor
Netrin-1
Floor
plate
Growth toward the floor
plate
Cell
adhesion
molecules
Growth across the midline
Slit
Slit receptor
No turning back
Growth of an interneuron axon toward and across the midline of the spinal cord
(diagrammed here in cross section)
LE 48-33b
Developing axon
of motor neuron
Netrin-1
receptor
Slit
receptor
Slit
Netrin-1
Growth of a motor neuron
axon away from the
midline of the spinal cord
• Genes and basic events in axon guidance are
similar in invertebrates and vertebrates
• Knowledge of these events may be applied one
day to stimulate axonal regrowth following CNS
damage
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Neural Stem Cells
• The adult human brain contains stem cells that
can differentiate into mature neurons
• Induction of stem cell differentiation and
transplantation of cultured stem cells are potential
methods for replacing neurons lost to trauma or
disease
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
10 µm
LE 48-34
Diseases and Disorders of the Nervous System
• Mental illnesses and neurological disorders take
an enormous toll on society, in both the patient’s
loss of a productive life and the high cost of longterm health care
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Schizophrenia
• About 1% of the world’s population suffers from
schizophrenia
• Schizophrenia is characterized by hallucinations,
delusions, blunted emotions, and other symptoms
• Available treatments focus on brain pathways that
use dopamine as a neurotransmitter
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Depression
• Two broad forms of depressive illness are known:
bipolar disorder and major depression
• Bipolar disorder is characterized by manic (highmood) and depressive (low-mood) phases
• In major depression, patients have a persistent
low mood
• Treatments for these types of depression include
drugs such as Prozac and lithium
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Alzheimer’s Disease
• Alzheimer’s disease (AD) is a mental deterioration
characterized by confusion, memory loss, and
other symptoms
• AD is caused by the formation of neurofibrillary
tangles and senile plaques in the brain
• A successful treatment in humans may hinge on
early detection of senile plaques
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-35
Senile plaque
Neurofibrillary tangle
20 µm
Parkinson’s Disease
• Parkinson’s disease is a motor disorder caused by
death of dopamine-secreting neurons in the
substantia nigra
• It is characterized by difficulty in initiating
movements, slowness of movement, and rigidity
• There is no cure, although various approaches are
used to manage symptoms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings