Download - Chapter 28 Nervous System
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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
Spinalcord
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• The late actor Christopher Reeve
– Suffered a spinal cord injury during an equestrian competition
– Was an influential advocate for spinal cord research
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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 data-processing systems on Earth
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• The nervous system obtains and processes sensory information
– And sends commands to effector cells, such as muscles, that carry out appropriate responses
Sensory input
Sensory receptor
Effector cells
Motor output
Integration
Peripheral nervous system (PNS)
Brain and spinal cord
Central nervoussystem (CNS)Figure 28.1A
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• 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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Quadricepsmuscles
Flexormuscles
Brain
Spinalcord
Nerve
PNS
Ganglion
CNS
• Automatic responses called reflexes
– Provide an example of nervous system function
Interneuron
4
Sensory neuron2
Motorneuron 3
1 Sensory receptor
Figure 28.1B
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• 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
Schwann cell
Signal direction Dendrites
Cell body
Nucleus
Axon
Schwann cell
Signalpathway
Myelin sheath
Nodes ofRanvier
Node of RanvierLayers of myelinin sheath
Nucleus
Synaptic terminals
Cell body
SE
M 3
,600
Figure 28.2
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• 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 potentialVoltmeter
Plasmamembrane Microelectrode
outside cell– 70 mV
Axon
Neuron
Microelectrodeinside cell
+ + + + + + + +
– – – – – – – –
– – – – – – – –
+ + + + + + + +
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+Na+
K+
Na+
Na+
Na+K+ Na+ Na+
Na+Na+
Na+Na+
K+
Protein
Na+
Plasmamembrane
K+ channel
K+
K+
K+K+K+
K+
K+
K+
Na+ - K+
pump
Na+
Na+
K+
Na+
channel
Inside of cellFigure 28.3B
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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
3
2
1
4
5
1
Na+
+ + + + + + +
– – + + – – –
– – + + – – –
+ + + + + + +
Additional Na+ channels open, K+ channels are closed; interior of cell becomes more positive.
A stimulus opens some Na+ channels; if threshold is reached, action potential is triggered.
Resting state: voltage-gated Na+ and K+ channels closed; resting potential is maintained.
Na+ channels close and inactivate. K+ channels open, and K+ rushes out; interior of cell more negative than outside.
The K+ channels closerelatively slowly, causinga brief undershoot.
Return to resting state.
Na+
+ + + + + + +
– – + – – – –
– – + – – – –
+ + + + + + +
+ + + + + + + +
– – – – – – – –
– – – – – – – –
+ + + + + + + +
+ + + + + + +
– – – – – – –
– – – – – – –
+ + + + + + +
+ + + + + + + +
– – – – – – – –
– – – – – – – –
+ + + + + + + +
Neuroninterior Neuron
interior
Actionpotential
Resting potential
Threshold
+50
0
– 50
– 100Time (msec)
K+
K+
Mem
bra
ne
pote
ntia
l(m
V) 3
1
2
4
51
Na+
Na+
Figure 28.4
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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
Action potential
Action potential
Axonsegment
Na
K
K
Na
K
K
Na
• Propagation of the action potential along an axon
1
2
3
Figure 28.5
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• 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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Sending neuron
Axon ofsendingneuron
Receivingneuron
Synapticcleft
Receivingneuron
Synapticterminal
Neurotransmittermolecules
Vesicles
Ion channels
Neurotransmitter brokendown and released
Ions
NeurotransmitterReceptor
Synapse
• Neuron communication
Vesicle fuseswith plasmamembrane
23
Neurotransmitteris released intosynaptic cleft
4Neurotransmitterbinds to receptor
1Actionpotentialarrives
5 Ion channel opens 6 Ion channel closesFigure 28.6
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28.7 Chemical synapses make complex information processing possible
• A neuron may receive information
– From hundreds of other neurons via thousands of synaptic terminals
Dendrites
Myelinsheath
Axon
Synaptic terminals
Inhibitory
Receivingcell body
Excitatory
Synapticterminals
SE
M 5
,500
Figure 28.7
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• 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
Nervenet
Neuron
A Hydra (cnidarian)Figure 28.10A
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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
B Flatworm (planarian)
Eyespot
Brain
Nervecord
Tranversenerve
E Squid (mollusc)
Brain
Giantaxon
Brain
Ventralnervecord
Segmentalganglion
C Leech (annelid)
Brain
Ventralnervecord
Ganglia
D Insect (arthropod)
Figure 28.10B–E
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28.11 Vertebrate nervous systems are highly centralized and cephalized
Central nervoussystem (CNS)
Brain
Spinal cord
Peripheralnervoussystem (PNS)
Cranialnerves
Gangliaoutside CNS
Spinalnerves
Figure 28.11A
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• The brain and spinal cord
– Contain fluid-filled spaces
BrainCerebrospinal fluid
Meninges
White matter
Gray matter Dorsal rootganglion(part of PNS)
Spinal nerve(part of PNS)
Central canal
Spinal cord(cross section)
Ventricles
Central canalof spinal cord
Spinal cord
Figure 28.11B
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• 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
Peripheralnervous system
Somaticnervoussystem
Autonomicnervoussystem
Sympatheticdivision
Parasympatheticdivision
Entericdivision
Figure 28.12
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• 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, energy-consuming activities
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• The autonomic nervous system
Parasympathetic division Sympathetic division
Eye
Salivaryglands
Lung
Liver
Heart Adrenalgland
Pancreas
Stomach
Intestines
Bladder
Genitalia
Spinalcord
Brain
Constrictspupil
Stimulatessalivaproduction
Constrictsbronchi
Slowsheart
Stimulatesstomach,pancreas,and intestines
Stimulatesurination
Promoteserection ofgenitals
Promotesejaculation and vaginalcontractions
Inhibitsurination
Inhibitsstomach,pancreas,and intestines
Stimulatesglucose release
Stimulatesepinephrineand norepinep-hrine release
Acceleratesheart
Dilates bronchi
Inhibitssalivaproduction
Dilatespupil
Figure 28.13
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28.14 The vertebrate brain develops from three anterior bulges of the neural tube
• The vertebrate brain
– Develops from the forebrain, midbrain, and hindbrain
EmbryonicBrain Regions
Brain StructuresPresent in Adult
Forebrain
Midbrain
Hindbrain
Midbrain Hindbrain
Forebrain
Embryo (one month old)
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
PonsCerebellum
Medullaoblongata
Spinal cord
Fetus (three months old)Figure 28.14
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• 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
Forebrain
Midbrain
Hindbrain
Cerebrum
Thalamus
Hypothalamus
Pituitary gland
Pons
Medullaoblongata
Cerebellum
Spinalcord
Cerebralcortex
Figure 28.15A
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• 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 cerebralhemisphere
Right cerebralhemisphere
Corpuscallosum
BasalgangliaFigure 28.15B
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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
Occipital lobeTemporal lobe
Frontalassociationarea M
otor
cor
tex
Som
atos
enso
ry c
orte
x
Somatosensory associationarea
Speech
TasteReading
Hearing
Smell
Auditory associationarea
Visual associationarea
Vision
Speech
Figure 28.16
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• 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
Eye
Reticular formation
Input from touch, pain,and temperature receptors
Input fromears
Data to cerebral cortex
Figure 28.18A
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• An EEG
– Measures brain waves during sleep and arousal
Awake but quiet (alpha waves)
Awake during intense mental activity (beta waves)
Asleep
Delta waves REM sleep Delta wavesFigure 28.18B, C
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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
Smell
Olfactorybulb Amygdala Hippocampus
Cerebrum
Thalamus
Hypothalamus
Prefrontalcortex
Figure 28.19
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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
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• Selective serotonin reuptake inhibitors (SSRIs)
– Are prescribed to treat depression
140
120
100
80
60
40
20
01995 1996 1997 1998 1999 2000 2001 2002 2003
Year
Pre
scrip
tions
(m
illio
ns)
Figure 28.20A
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Alzheimer’s Disease
• Alzheimer’s disease (AD)
– Is characterized by confusion, memory loss, and a variety of other symptoms
Senile plaque Neurofibrillary tangle
LM
25
0
Figure 28.20B
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Parkinson’s Disease
• Parkinson’s disease is a motor disorder
– Characterized by difficulty in initiating movements, slowness of movement, and rigidity
Figure 28.20C