the nervous system. functions of the nervous system figure 7.1
DESCRIPTION
Functions of the Nervous System Sensory input—gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration To process and interpret sensory input and decide if action is neededTRANSCRIPT
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The Nervous System
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Functions of the Nervous System
Figure 7.1
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Functions of the Nervous SystemSensory input—gathering information
To monitor changes occurring inside and outside the body
Changes = stimuliIntegration
To process and interpret sensory input and decide if action is needed
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Functions of the Nervous SystemMotor output
A response to integrated stimuliThe response activates muscles or glands
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Organization of the Nervous System
Figure 7.2
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Structural Classification of the Nervous SystemCentral nervous system (CNS)
BrainSpinal cord
Peripheral nervous system (PNS)Nerves outside the brain and spinal cord
Spinal nerves Cranial nerves
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Functional Classification of the Peripheral Nervous System
Sensory (afferent) divisionNerve fibers that carry information to the
central nervous systemMotor (efferent) division
Nerve fibers that carry impulses away from the central nervous system
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Functional Classification ofthe Peripheral Nervous SystemMotor (efferent) division (continued)
Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary
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Neuron Classification
Figure 7.6
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Figure 7.4
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Neurons= nerve cellsCells specialized to transmit messages
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Nervous Tissue: NeuronsCell body
NucleusLarge nucleolus
Processes outside the cell bodyDendrites—conduct impulses toward the cell
bodyAxons—conduct impulses away from the cell
body
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Figure 7.4
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Nervous Tissue: Neurons
Figure 7.5
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Nervous Tissue: NeuronsMyelin sheath—whitish, fatty material
covering axonsSchwann cells—produce myelin sheaths in
jelly roll–like fashionNodes of Ranvier—gaps in myelin sheath
along the axonNeurilemma – exposed layer of cell
membrane of Schwann cells
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Nervous Tissue: NeuronsAxons end in axonal terminalsMost cells average about 10,000 axon
terminalsAxon terminals contain vesicles with
neurotransmitters (chemicals that excite or inhibit neurons or effector cells)
Axon terminals are separated from the next neuron by a gapSynaptic cleft—gap between adjacent neuronsSynapse—junction between nerves
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Neuron Cell Body LocationMost neuron cell bodies are found in the
central nervous systemWhite matter – condensed areas of
myelinated fibersGray matter—areas of unmyelinated fibers
Ganglia—collections of cell bodies outside the central nervous system
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Figure 7.8a
Structural Classification of NeuronsMultipolar neurons—many extensions from
the cell body
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Structural Classification of NeuronsBipolar neurons—one axon and one dendrite
Figure 7.8b
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Structural Classification of NeuronsUnipolar neurons—have a short single
process leaving the cell body
Figure 7.8c
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Nerve ImpulseThe principle way neurons communicate is
by generating and propagating ACTION POTENTIALS (Aps).
Only cells with excitable membranes (like muscle cells and neurons) can generate APs.
An AP is a brief reversal of membrane potential.
In neurons, an AP is called a NERVE IMPULSE and only axons can generate one.
An AP involves the movement of Na+ and K+ ions moving in and out of the neuron, resulting in changes in POLARITY.
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All or None ResponseIf the action potential (nerve impulse) starts, it is propagated over the entire axon
There are NO partial impulses. The impulse happens completely or not at all.
Impulses travel faster when fibers have a myelin sheath.
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Transmission of a Signal at SynapsesImpulses are able to cross the synapse to
another nerveNeurotransmitter is released from a nerve’s
axon terminalThe dendrite of the next neuron has receptors
that are stimulated by the neurotransmitterAn action potential is started in the dendrite
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Transmission of a Signal at Synapses
Figure 7.10
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Receptor
Neurotransmitter
Na+Na+
Neurotransmitterbroken downand released
Ion channel opens Ion channel closes
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Transmission of a Signal at Synapses
Figure 7.10, step 1
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmitting
neuron
Receivingneuron
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Figure 7.10, step 2
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Vesiclefuses withplasmamembrane
Synaptic cleft
Ion channels Receiving neuron
Transmitting neuron
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Figure 7.10, step 3
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
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Figure 7.10, step 4
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
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Figure 7.10, step 5
SynapseReceivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Receptor
Neurotransmitter
Na+
Ion channel opens
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Transmission of a Signal at Synapses
Figure 7.10, step 6
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Receptor
Neurotransmitter
Na+
Na+
Neurotransmitterbroken downand released
Ion channel opens Ion channel closes
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Figure 7.10, step 7
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channelsReceiving neuron
Transmitting neuron
Receptor
Neurotransmitter
Na+
Na+
Neurotransmitterbroken downand released
Ion channel opens Ion channel closes
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Nerve ImpulsesResting neuron
The plasma membrane at rest is polarizedFewer positive ions are inside the cell than
outside the cellDepolarization
A stimulus depolarizes the neuron’s membraneA depolarized membrane allows sodium (Na+)
to flow inside the membraneThe exchange of ions initiates an action
potential in the neuron
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Nerve ImpulsesAction potential
If the action potential (nerve impulse) starts, it is propagated over the entire axon
Impulses travel faster when fibers have a myelin sheath
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Nerve ImpulsesRepolarization
Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane
The sodium-potassium pump, using ATP, restores the original configuration
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Nerve Impulses
Figure 7.9a–b
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Nerve Impulses
Figure 7.9c–d
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Nerve Impulses
Figure 7.9e–f