Chapter 28 Nervous Systems · Central nervous system (CNS) –The brain and spinal cord –Contains...
Transcript of Chapter 28 Nervous Systems · Central nervous system (CNS) –The brain and spinal cord –Contains...
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PowerPoint Lectures for
Biology: Concepts & Connections, Sixth Edition
Campbell, Reece, Taylor, Simon, and Dickey
Chapter 28 Nervous Systems
Lecture by Edward J. Zalisko
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Introduction: Can an Injured Spinal Cord Be Fixed?
Spinal cord injuries disrupt communication between
– The central nervous system (brain and spinal cord)
– The rest of the body
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Spinalcord
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The late actor Christopher Reeve
– Suffered a spinal cord injury during an equestrian competition in 1995
– Was an influential advocate for spinal cord research
– Died of complications to the injury in 2004
Introduction: Can an Injured Spinal Cord Be Fixed?
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Over 10,000 Americans suffer spinal cord injuries each year
Current research shows promise
– Steroids reduce damage if used within hours of damage
– Coaxing damaged nerve cells to regenerate
– Transplants of nerve cells or stem cells
Introduction: Can an Injured Spinal Cord Be Fixed?
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NERVOUS SYSTEM STRUCTURE
AND FUNCTION
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28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands
The nervous system
– Obtains sensory information
– Processes sensory information
– Sends commands to effector cells (muscles) that carry out appropriate responses
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Sensory input
Sensory receptor
Integration
Motor output
Effector cells
Brain and spinal cord
Peripheral nervoussystem (PNS)
Central nervoussystem (CNS)
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The central nervous system (CNS) consists of
– Brain
– Spinal cord (vertebrates)
Peripheral nervous system (PNS)
– Located outside the CNS
– Consists of
– Nerves (bundles of fibers of sensory and motor neurons) and
– Ganglia (clusters of cell bodies of the neurons)
28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands
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Sensory neurons
– Conduct signals from sensory receptors
– To the CNS
Interneurons in the CNS
– Integrate information
– Send it to motor neurons
Motor neurons convey signals to effector cells
28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands
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Sensory
receptor
12
3
4
Sensory neuron
Brain
Spinalcord
Ganglion
Motorneuron
Quadricepsmuscles
Flexormuscles
Nerve
Interneuron
CNS
PNS
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28.2 Neurons are the functional units of nervous systems
Neurons are
– Cells specialized for carrying signals
– The functional units of the nervous system
A neuron consists of
– A cell body
– Two types of extensions (fibers) that conduct signals
– Dendrites
– Axons
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Myelin sheaths
– Enclose axons
– Form a cellular insulation
– Speed up signal transmission
28.2 Neurons are the functional units of nervous systems
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Signal directionDendrites
Cellbody
Nucleus Axon
Schwanncell
Myelin sheath
Signalpathway
Nodes ofRanvier
Synaptic terminals
Node ofRanvier
NucleusSchwanncell
Layers ofmyelin sheaths
Cell Body
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NERVE SIGNALS AND THEIR TRANSMISSION
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28.3 A neuron maintains a membrane potential across its membrane
At rest, a neuron’s plasma membrane
– Has potential energy—the membrane potential
– Just inside the cell is slightly negative
– Just outside the cell is slightly positive
– Resting potential—voltage across the plasma membrane
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The resting potential exists because of differences in ion concentration inside and outside a cell
– Inside a cell
– K+ high
– Na+ low
– Outside a cell
– K+ low
– Na+ high
28.3 A neuron maintains a membrane potential across its membrane
Animation: Resting Potential
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Neuron Axon
Plasmamembrane
Outside of cell Na+ K+
Na+
Na+
Na+-K+
pump
Na+
channel
Plasmamembrane
K+ channel
Protein
Inside of cell
Na+
Na+ Na+
Na+
Na+
Na+
Na+Na+
K+ Na+
Na+
Na+
Na+
K+
K+K+
K+
K+
K+
K+
K+
K+
K+
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28.4 A nerve signal begins as a change in the membrane potential
A stimulus
– Alters the permeability of a section of membrane
– Allows ions to pass through
– Changes the membrane’s voltage
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A nerve signal—an action potential
– A change in the membrane voltage
– From the resting potential
– To a maximum level
– And back to the resting potential
28.4 A nerve signal begins as a change in the membrane potential
Animation: Action Potential
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Na+
K+
Additional Na channels open,
K channels are closed; interior of
cell becomes more positive.
1
2
3
K+
Na+
A stimulus opens some Na
channels; if threshold is reached,
action potential is triggered.
Na+
Sodium
channel
Potassium
channel
Neuroninterior
Plasmamembrane
K+
Resting state: voltage-gated Na
and K channels closed; restingpotential is maintained.
Na+
K+
4
5
1
Na+
K+
Neuron
interior
Na channels close and
inactivate. K channels
open, and K rushes
out; interior of cell more
negative than outside.
The K channels
close relatively
slowly, causing a
brief undershoot.
Return to resting state.
Me
mb
ran
e p
ote
nti
al
(mV
)
Actionpotential
Threshold
Resting potential
Time (msec)
50
0
–50
–100
1
2
3
4
51
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1
Neuron interior
Na+
K+
Time (msec)–100
Resting potential
1
Threshold–50
0
50Actionpotential
Mem
bra
ne p
ote
nti
al
(mV
)
Plasmamembrane
Sodiumchannel
Potassiumchannel
Resting state: voltage-gated
Na and K channels closed;
resting potential is maintained.
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2 Na+
K+
Time (msec)–100
Resting potential
1
Threshold
2
–50
0
50Actionpotential
Mem
bra
ne p
ote
nti
al
(mV
)
A stimulus openssome Na channels;if threshold is reached,
action potential istriggered.
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3 Na+
K+
Time (msec)–100
Resting potential
1
Threshold
2
3
–50
0
50Actionpotential
Mem
bra
ne p
ote
nti
al
(mV
)
Additional Na channelsopen, K channels areclosed; interior of cellbecomes more positive.
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4 Na+
K+
Time (msec)–100
Resting potential
1
Threshold
2
34
–50
0
50Actionpotential
Mem
bra
ne p
ote
nti
al
(mV
)
Na channels close andinactivate. K channelsopen, and K rushes out;interior of cell morenegative than outside.
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5
Time (msec)–100
Resting potential
1
Threshold
2
34
5
–50
0
50Actionpotential
Mem
bra
ne p
ote
nti
al
(mV
)
The K channelsclose relativelyslowly, causing abrief undershoot.
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Return to resting state.1
Neuroninterior
Na+
K+
Time (msec)–100
Resting potential
1
Threshold
2
34
5
–50
0
50
1
Actionpotential
Mem
bra
ne p
ote
nti
al
(mV
)
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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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Axon
Action potential
Axonsegment
1Na+
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Axon
Action potential
Axonsegment
Action potential
2
1Na+
Na+
K+
K+
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Axon
Action potential
Axonsegment
Action potential
Action potential
2
3
1Na+
Na+
Na+
K+
K+
K+
K+
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The strength of the stimulus changes
– The frequency of action potentials
– But not the strength of action potentials
28.5 The action potential propagates itself along the neuron
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28.6 Neurons communicate at synapses
Synapses are junctions where signals are transmitted between
– Two neurons
– Or between neurons and effector cells
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Electrical synapses
– Electrical signals pass between cells
Chemical synapses
– Sending (presynaptic) cell secretes a chemical signal, a neurotransmitter
– The neurotransmitter crosses the synaptic cleft
– The neurotransmitter binds to a receptor on the surface of the receiving (postsynaptic) cell
28.6 Neurons communicate at synapses
Animation: Synapse
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Sending neuron 1
23
4
65
Axon ofsendingneuron
Vesicles
Synapticterminal
Vesicle fuseswith plasmamembrane
Synapticcleft
Receivingneuron
Receivingneuron
Ion channels
Neurotransmittermolecules
Neurotransmitteris released into synaptic cleft
Neurotransmitterbinds to receptor
Synapse
Actionpotentialarrives
Neurotransmitter
Receptor
Ions
Neurotransmitter brokendown and released
Ion channel closesIon channel opens
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Sending neuron
4
Axon ofsendingneuron
Vesicles
Synapticterminal
Vesicle fuseswith plasmamembrane
Synapticcleft
Receivingneuron
Receivingneuron
Ion channels
Neurotransmittermolecules
Neurotransmitteris released into synaptic cleft
Neurotransmitterbinds to receptor
Synapse
Actionpotentialarrives
32
1
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5
Neurotransmitter
Ion channel closesIon channel opens
Receptor
Ions
Neurotransmitter broken
down and released
6
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28.7 Chemical synapses make complex information processing possible
Some neurotransmitters
– Excite the receiving cell
– Inhibit the receiving cell’s activity by decreasing its ability to develop action potentials
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A neuron may receive information
– From hundreds of other neurons
– Via thousands of synaptic terminals
The summation of excitation and inhibition
– Determines if a neuron will transmit a nerve signal
28.7 Chemical synapses make complex information processing possible
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Dendrites
Myelinsheath
Axon
Receivingcell body
Inhibitory Excitatory
Synaptic terminals
Synaptic
terminals
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Dendrites
Myelinsheath
Axon
Receivingcell body
Inhibitory Excitatory
Synaptic terminals
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Synapticterminals
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28.8 A variety of small molecules function as neurotransmitters
Many small, nitrogen-containing molecule serve as neurotransmitters
– Acetylcholine is a neurotransmitter
– In the brain
– Between neurons and muscle cells
– Biogenic amines
– Important in the CNS
– Serotonin and dopamine affect sleep, mood, attention
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– Amino acids important in the CNS
– Some are excitatory
– Some are inhibitory
– Neuropeptides
– Substance P mediates perceptions of pain
– Endorphins decrease perception of pain
– Nitric oxide
– A dissolved gas
– Triggers erections
28.8 A variety of small molecules function as neurotransmitters
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28.9 CONNECTION: Many drugs act at chemical synapses
Many psychoactive drugs
– Act at synapses
– Affect neurotransmitter action
Caffeine counts inhibitory neurotransmitters
Nicotine acts as a stimulant
Alcohol is a depressant
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AN OVERVIEW OF ANIMAL
NERVOUS SYSTEMS
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28.10 EVOLUTION CONNECTION: The evolution of animal nervous systems reflects changes in body symmetry
Radially symmetrical animals
– Nervous system arranged in a weblike system of neurons
– Nerve net
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Nervenet
Neuron
Hydra (cnidarian)A
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Most bilaterally symmetrical animals exhibit
– Centralization—presence of a central nervous system
– Cephalization—concentration of the nervous system in the head region
28.10 EVOLUTION CONNECTION: The evolution of animal nervous systems reflects changes in body symmetry
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Eyespot
B
Brain
Nervecord
Transversenerve
Flatworm (planarian)
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Brain
C
Ventralnervecord
Segmentalganglion
Leech (annelid)
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Brain
D
Ventralnervecord
Ganglia
Insect (arthropod)
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Brain
E
Giantaxon
Squid (mollusc)
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28.11 Vertebrate nervous systems are highly centralized and cephalized
Vertebrate nervous systems are
– Highly centralized
– Cephalized
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Central nervous system (CNS)
– The brain and spinal cord
– Contains fluid-filled spaces
– In ventricles of the brain
– In the central canal of the spinal cord
– Surrounding the brain
Peripheral nervous system (PNS)
– Nerves—cranial nerves and spinal nerves
– Ganglia
28.11 Vertebrate nervous systems are highly centralized and cephalized
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Brain
Central nervoussystem (CNS)
Spinal cord
Peripheralnervous
system (PNS)
Cranialnerves
Gangliaoutside
CNS
Spinalnerves
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Brain
Ventricles
Central canalof spinal cord
Cerebrospinal fluid
Meninges
Spinal cord
Whitematter
Graymatter Dorsal root
ganglion(part of PNS)
Spinal nerve(part of PNS)Central canal
Spinal cord(cross section)
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28.12 The peripheral nervous system of vertebrates is a functional hierarchy
Two functional components of the PNS
– Somatic nervous system—mostly voluntary
– Autonomic nervous system (ANS)—mostly involuntary
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Somatic nervous system
– Carries signals to and from skeletal muscles
– Mainly in response to external stimuli
Autonomic nervous system
– Regulates the internal environment
– Controls
– Smooth muscle
– Cardiac muscle
– Organs of various body systems
28.12 The peripheral nervous system of vertebrates is a functional hierarchy
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Peripheralnervous system
Somaticnervoussystem
Autonomicnervoussystem
Sympatheticdivision
Parasympatheticdivision
Entericdivision
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28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment
Parasympathetic division of ANS
– Primes the body for activities that gain and conserve energy for the body
Sympathetic division of ANS
– Prepares the body for intense, energy-consuming activities
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Brain
Parasympathetic division
Constrictspupil
Eye
Stimulatessalivaproduction
Lung
Constrictsbronchi
Slowsheart
Spinalcord
Stimulatesstomach,pancreas,and intestines
Liver
Stimulatesurination
Promoteserection ofgenitals
Intestines
Genitalia
Bladder
Pancreas
Stomach
Adrenalgland
Heart
Salivaryglands
Sympathetic division
Dilatespupil
Inhibitssalivaproduction
Dilatesbronchi
Acceleratesheart
Stimulatesepinephrineand norepi-nephrine release
Stimulatesglucose release
Inhibitsstomach,pancreas,and intestines
Inhibitsurination
Promotes ejacu-lation and vaginalcontractions
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28.14 The vertebrate brain develops from three anterior bulges of the neural tube
The vertebrate brain evolved by the enlargement and subdivision of the
– Forebrain
– Midbrain
– Hindbrain
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EmbryonicBrain Regions
Forebrain
Midbrain
Hindbrain
Midbrain
Hindbrain
Forebrain
Embryo (one month old)
Brain StructuresPresent in Adult
Cerebrum (cerebral hemispheres; includescerebral cortex, white matter, basal ganglia)
Diencephalon (thalamus, hypothalamus,posterior pituitary, pineal gland)
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Medulla oblongata (part of brainstem)
Cerebralhemisphere Diencephalon
Midbrain
Pons
Cerebellum
Medullaoblongata
Spinal cord
Fetus (three months old)
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EmbryonicBrain Regions
Brain StructuresPresent in Adult
Cerebrum (cerebral hemispheres; includescerebral cortex, white matter, basal ganglia)
Diencephalon (thalamus, hypothalamus,posterior pituitary, pineal gland)
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Medulla oblongata (part of brainstem)
Forebrain
Midbrain
Hindbrain
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Midbrain
Hindbrain
Forebrain
Embryo (one month old)
Cerebralhemisphere Diencephalon
Midbrain
Pons
Cerebellum
Medullaoblongata
Spinal cord
Fetus (three months old)
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In birds and mammals
– Size and complexity of the cerebrum
– Correlates with their sophisticated behavior
28.14 The vertebrate brain develops from three anterior bulges of the neural tube
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THE HUMAN BRAIN
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28.15 The structure of a living supercomputer: The human brain
The human brain
– More powerful than the most sophisticated computer
– Composed of three main parts
– Forebrain
– Midbrain
– Hindbrain
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Midbrain
Hindbrain
Forebrain
Cerebrum
Thalamus
Hypothalamus
Pituitary gland
Pons
Medullaoblongata
Cerebellum
Cerebral
cortex
Spinalcord
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Left cerebralhemisphere
Right cerebralhemisphere
Corpuscallosum
Basalganglia
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Midbrain, subdivisions of the hindbrain, thalamus, and hypothalamus
– Conduct information to and from higher brain centers
– Regulate homeostatic functions
– Keep track of body position
– Sort sensory information
28.15 The structure of a living supercomputer: The human brain
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Cerebrum
– Part of the forebrain
– Largest and most complex part of the brain
– Most integrative power is in the cerebral cortex
28.15 The structure of a living supercomputer: The human brain
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28.16 The cerebral cortex is a mosaic of specialized, interactive regions
Cerebral cortex
– About 5 mm thick
– Accounts for 80% of brain mass
– Specialized integrative regions
– Somatosensory cortex
– Centers for vision, hearing, taste, and smell
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Motor cortex—directs responses
Association areas
– Make up most of the cerebrum
– Higher mental activities
– Reasoning
– Language
Right and left cerebral hemispheres
– Specialize in different mental tasks
28.16 The cerebral cortex is a mosaic of specialized, interactive regions
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Frontal lobe Parietal lobe
Temporal lobe Occipital lobe
Frontal association
area
Somatosensoryassociationarea
Visualassociation
areaAuditory association
area
Speech
Smell
Hearing
Taste
Speech
Reading
Vision
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28.17 CONNECTION: Injuries and brain operations provide insight into brain function
Brain injuries and surgeries reveal brain functions
– The case of Phineas Gage
– Stimulation of the cerebral cortex during surgery
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28.18 CONNECTION: fMRI scans can provide insight into brain structure and function
fMRI
– A scanning and imaging technology used to study brain functions
– Used on conscious patients
– Monitors changes in blood oxygen usage in the brain
– Correlates to regions of intense brain function
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28.19 Several parts of the brain regulate sleep and arousal
Sleep and arousal involve activity by the
– Hypothalamus
– Medulla oblongata
– Pons
– Neurons of the reticular formation
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Sleep
– Is essential for survival
– Sleep is an active state
– Sleep may be involved in consolidating learning and memory
28.19 Several parts of the brain regulate sleep and arousal
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28.20 The limbic system is involved in emotions, memory, and learning
The limbic system
– Is a functional group of integrating centers in
– Cerebral cortex
– Thalamus
– Hypothalamus
– Is involved in
– Emotions
– Memory
– Learning
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Cerebrum
ThalamusHypothalamus
Prefrontalcortex
Olfactorybulb
Amygdala Hippocampus
Smell
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28.21 CONNECTION: Changes in brain physiology can produce neurological disorders
Many neurological disorders can be linked to changes in brain physiology
– Schizophrenia
– Depression
– Alzheimer’s disease
– Parkinson’s disease
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28.21 CONNECTION: Changes in brain physiology can produce neurological disorders
Schizophrenia
– A severe mental disturbance
– Characterized by psychotic episodes in which patients lose the ability to distinguish reality
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28.21 CONNECTION: Changes in brain physiology can produce neurological disorders
Depression
– Two broad forms of depressive illness have been identified
– Major depression
– Bipolar disorder—manic-depressive disorder
– Treatments may include selective serotonin reuptake inhibitors (SSRIs)
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Year
Pre
scri
pti
on
s (
mil
lio
ns)
1995 96 97 98 99 2000 01 02 03 04 05 060
20
40
60
80
100
120
140
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Alzheimer’s disease is characterized by
– Confusion
– Memory loss
A firm diagnosis is difficult to make
28.21 CONNECTION: Changes in brain physiology can produce neurological disorders
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Parkinson’s disease
– Motor disorder
– Characterized by
– Difficulty in initiating movements
– Slowness of movement
– Rigidity
28.21 CONNECTION: Changes in brain physiology can produce neurological disorders
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Sensoryreceptor
Effectorcells
Sensory input
Integration
Motor output
PNS CNS
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Dendrites
Cellbody
AxonMyelin
(speeds signaltransmission)
Synapticterminals
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Nervous system
CNS PNS
Brain Spinal cordSomatic: voluntary
control over musclesAutonomic: involuntary
control over organs
Sympatheticdivision:
fight or flight
Parasympatheticdivision:
rest and digest
Enteric: regulatedby sympathetic and
parasympathetic
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c.
d.
e.
h.
brain
b. a.
f. g.
i.
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1. Describe the structural and functional subdivisions of the nervous system
2. Describe the three parts of a reflex, noting the three types of neurons involved in the reaction
3. Explain how an action potential is produced and the resting membrane potential restored
4. Compare the structures, functions, and locations of electrical and chemical synapses
You should now be able to
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Copyright © 2009 Pearson Education, Inc.
5. Describe the types and functions of neurotransmitters known in humans
6. Explain how drugs can alter chemical synapses
7. Describe the diversity of animal nervous systems
8. Describe the general structure of the brain, spinal cord, and associated nerves of vertebrates
9. Compare the functions of the somatic nervous system and autonomic nervous system
You should now be able to
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Copyright © 2009 Pearson Education, Inc.
You should now be able to
10. Describe the parts and functions of the human brain
11. Explain how injuries, illness, and surgery provide insight into the functions of the brain
12. Describe the causes, symptoms, and treatments of schizophrenia, depression, Alzheimer’s disease, and Parkinson’s disease