Post on 10-May-2015
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PowerPoint® Lecture Slidesprepared byMeg FlemmingAustin Community College
C H A P T E R 8
The Nervous System
© 2013 Pearson Education, Inc.
Chapter 8 Learning Outcomes
• 8-1 • Describe the anatomical and functional divisions of the nervous
system.• 8-2
• Distinguish between neurons and neuroglia on the basis of structure and function.
• 8-3 • Describe the events involved in the generation and propagation of
an action potential.• 8-4
• Describe the structure of a synapse, and explain the mechanism of nerve impulse transmission at a synapse.
• 8-5• Describe the three meningeal layers that surround the central
nervous system.
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Chapter 8 Learning Outcomes
• 8-6 • Discuss the roles of gray matter and white matter in the spinal cord.
• 8-7 • Name the major regions of the brain, and describe the locations
and functions of each.• 8-8
• Name the cranial nerves, relate each pair of cranial nerves to its principal functions, and relate the distribution pattern of spinal nerves to the regions they innervate.
• 8-9 • Describe the steps in a reflex arc.
• 8-10 • Identify the principal sensory and motor pathways, and explain how
it is possible to distinguish among sensations that originate in different areas of the body.
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Chapter 8 Learning Outcomes
• 8-11• Describe the structures and functions of the sympathetic and
parasympathetic divisions of the autonomic nervous system.• 8-12
• Summarize the effects of aging on the nervous system.• 8-13
• Give examples of interactions between the nervous system and other organ systems.
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The Nervous System and the Endocrine System (Introduction)
• The nervous system and endocrine system
coordinate other organ systems to maintain
homeostasis
• The nervous system is fast, short acting
• The endocrine system is slower, but longer lasting
• The nervous system is the most complex system
in the body
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Functions of the Nervous System (8-1)
• Monitors the body's internal and external
environments
• Integrates sensory information
• Coordinates voluntary and involuntary responses
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Divisions of the Nervous System (8-1)
• Anatomical divisions are:
• The central nervous system (CNS)
• Made up of the brain and spinal cord
• Integrates and coordinates input and output
• The peripheral nervous system (PNS)
• All the neural tissues outside of the CNS
• The connection between the CNS and the organs
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Divisions of the Nervous System (8-1)
• Functional divisions are:
• The afferent division
• Includes sensory receptors and neurons that send
information to the CNS
• The efferent division
• Includes neurons that send information to the effectors,
which are the muscles and glands
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Efferent Division of the Nervous System (8-1)
• Further divided into:
• The somatic nervous system (SNS)
• Controls skeletal muscle
• The autonomic nervous system (ANS)
• Controls smooth and cardiac muscle, and glands
• Has two parts
1. Sympathetic division
2. Parasympathetic division
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Figure 8-1 A Functional Overview of the Nervous System.
CENTRAL NERVOUS SYSTEM
PERIPHERAL NERVOUSSYSTEM
Sensory informationwithin
afferent division
Informationprocessing
Motor commandswithin
efferent division
includes
Somaticnervoussystem
Autonomicnervous system
Parasympatheticdivision
Sympatheticdivision
Receptors Effectors
Somatic sensoryreceptors (monitorthe outside worldand our position
in it)
Visceral sensoryreceptors (monitorinternal conditions
and the statusof other organ
systems)
Skeletalmuscle
Smoothmuscle
Glands
Cardiacmuscle
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Checkpoint (8-1)
1. Identify the two anatomical divisions of the
nervous system.
2. Identify the two functional divisions of the
peripheral nervous system, and describe their
primary functions.
3. What would be the effect of damage to the
afferent division of the PNS?
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Neurons (8-2)
• Cells that communicate with one another and other cells
• Basic structure of a neuron includes:
• Cell body
• Dendrites
• Which receive signals
• Axons
• Which carry signals to the next cell
• Axon terminals
• Bulb-shaped endings that form a synapse with the next cell
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Neurons (8-2)
• Have a very limited ability to regenerate when
damaged or destroyed
• Cell bodies contain:
• Mitochondria, free and fixed ribosomes, and rough
endoplasmic reticulum
• Free ribosomes and RER form Nissl bodies and give the
tissue a gray color (gray matter)
• The axon hillock
• Where electrical signal begins
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Cell bodyMitochondrionGolgi apparatusAxon hillock
Dendrite
Nucleus
Nucleolus
Nissl bodies
Axon (may be myelinated)
CollateralAxon terminals
Nucleolus
Nucleus
Axon hillock
Nissl bodies
Nerve cell body
Nerve cell bodyLM x 1500
Figure 8-2 The Anatomy of a Representative Neuron.
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Structural Classification of Neurons (8-2)
• Based on the relationship of the dendrites to the cell body
• Multipolar neurons
• Are the most common in the CNS and have two or more dendrites and
one axon
• Unipolar neurons
• Have the cell body off to one side, most abundant in the afferent
division
• Bipolar neurons
• Have one dendrite and one axon with the cell body in the middle, and
are rare
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Multipolar neuron
Unipolar neuron
Bipolar neuron
Figure 8-3 A Structural Classification of Neurons.
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Sensory Neurons (8-2)
• Also called afferent neurons
• Total 10 million or more
• Receive information from sensory receptors
• Somatic sensory receptors
• Detect stimuli concerning the outside world, in the form of
external receptors
• And our position in it, in the form of proprioceptors
• Visceral or internal receptors
• Monitor the internal organs
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Motor Neurons (8-2)
• Also called efferent neurons
• Total about half a million in number
• Carry information to peripheral targets called
effectors
• Somatic motor neurons
• Innervate skeletal muscle
• Visceral motor neurons
• Innervate cardiac muscle, smooth muscle, and glands
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Interneurons (8-2)
• Also called association neurons
• By far the most numerous type at about 20 billion
• Are located in the CNS
• Function as links between sensory and motor
processes
• Have higher functions
• Such as memory, planning, and learning
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Neuroglial Cells (8-2)
• Are supportive cells and make up about half of all neural
tissue
• Four types are found in the CNS
1. Astrocytes
2. Oligodendrocytes
3. Microglia
4. Ependymal cells
• Two types in the PNS
1. Satellite cells
2. Schwann cells
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Astrocytes (8-2)
• Large and numerous neuroglia in the CNS
• Maintain the blood–brain barrier
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Oligodendrocytes (8-2)
• Found in the CNS
• Produce an insulating membranous wrapping
around axons called myelin
• Small gaps between the wrappings called nodes of Ranvier
• Myelinated axons constitute the white matter of
the CNS
• Where cell bodies are gray matter
• Some axons are unmyelinated
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Microglia (8-2)
• The smallest and least numerous
• Phagocytic cells derived from white blood cells
• Perform essential protective functions such as
engulfing pathogens and cellular waste
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Ependymal Cells (8-2)
• Line the fluid-filled central canal of the spinal cord
and the ventricles of the brain
• The endothelial lining is called the ependyma
• It is involved in producing and circulating
cerebrospinal fluid around the CNS
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Gray matterWhite matter
Graymatter
Neurons
Myelinatedaxons
Ependymal cells
CENTRALCANAL
Microglialcell
Inter-node
Whitematter
AxonNode
Oligoden-drocyte
Astrocyte
CapillaryBasementmembrane
Myelin(cut)
Figure 8-4 Neuroglia in the CNS.
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Neuroglial Cells in PNS (8-2)
• Satellite cells
• Surround and support neuron cell bodies
• Similar in function to the astrocytes in the CNS
• Schwann cells
• Cover every axon in PNS
• The surface is the neurilemma
• Produce myelin
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Schwann cell nucleus
Axons
Neurilemma
Myelin coveringinternode
Schwann cell nucleus
Nodes
Myelinated axon
Unmyelinated axon
A myelinated axon in the PNS is covered by several Schwann cells, each of which forms a myelin sheath around a portion of the axon. This arrangement differs from the way myelin forms in the CNS; compare with Figure 8-4.
A single Schwann cell can encircle several unmy-elinated axons. Every axon in the PNS is completely enclosed by Schwann cells.
TEM x 14,048
TEM x 14,048
Figure 8-5 Schwann Cells and Peripheral Axons.
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Organization of the Nervous System (8-2)
• In the PNS:
• Collections of nerve cell bodies are ganglia
• Bundled axons are nerves
• Including spinal nerves and cranial nerves
• Can have both sensory and motor components
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Organization of the Nervous System (8-2)
• In the CNS:
• Collections of neuron cell bodies are found in centers,
or nuclei
• Neural cortex is a thick layer of gray matter
• White matter in the CNS is formed by bundles of axons
called tracts, and in the spinal cord, form columns
• Pathways are either sensory or ascending tracts, or
motor or descending tracts
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PERIPHERAL NERVOUS SYSTEM
GRAY MATTER
GangliaCollections of neuron cell bodies in the PNS
WHITE MATTER
NervesBundles of axons in the PNS
RECEPTORS
EFFECTORS
PATHWAYSCenters and tracts that connectthe brain with other organs andsystems in the body
Ascending (sensory) pathwayDescending (motor) pathway
CENTRAL NERVOUS SYSTEM
GRAY MATTER ORGANIZATION
Neural CortexGray matter onthe surface ofthe brain
CentersCollections ofneuron cell bodiesin the CNS; eachcenter has specificprocessingfunctions Nuclei
Collections ofneuron cellbodies in theinterior of theCNS
Higher CentersThe most complexcenters in thebrain
WHITE MATTER ORGANIZATION
Tracts
Bundles of CNSaxons that share a common origin,destination, and function
ColumnsSeveral tractsthat form ananatomicallydistinct mass
Figure 8-6 The Anatomical Organization of the Nervous System.
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Checkpoint (8-2)
4. Name the structural components of a typical neuron.
5. Examination of a tissue sample reveals unipolar neurons.
Are these more likely to be sensory neurons or motor
neurons?
6. Identify the neuroglia of the central nervous system.
7. Which type of glial cell would increase in number in the
brain tissue of a person with a CNS infection?
8. In the PNS, neuron cell bodies are located in ________
and surrounded by neuroglial cells called ________ cells.
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The Membrane Potential (8-3)
• A membrane potential exists because of:
• Excessive positive ionic charges on the outside of the
cell
• Excessive negative charges on the inside, creating a
polarized membrane
• An undisturbed cell has a resting membrane potential
measured in the inside of the cell in millivolts
• The resting membrane potential of neurons is –70 mV
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Factors Determining Membrane Potential (8-3)
• Extracellular fluid (ECF) is high in Na+ and CI–
• Intracellular fluid (ICF) is high in K+ and negatively charged
proteins (Pr –)
• Proteins are non-permeating, staying in the ICF
• Some ion channels are always open
• Called leak channels
• Some are open or closed
• Called gated channels
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Factors Determining Membrane Potential (8-3)
• Na+ can leak in
• But the membrane is more permeable to K+
• Allowing K+ to leak out faster
• Na+/K+ exchange pump exchanges 3 Na+ for every
2 K+
• Moving Na+ out as fast as it leaks in
• Cell experiences a net loss of positive ions
• Resulting in a resting membrane charge of –70 mV
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EXTRACELLULAR FLUID
K+ leakchannel
Sodium–potassiumexchange
pump
Na+ leakchannel
Plasmamembrane
CYTOSOL
Protein
Protein
Sodium ion (Na+)
Potassium ion (K+)
Chloride ion (Cl–)
Protein
–70 –30+30
0
mV
KEY
Figure 8-7 The Resting Potential Is the Membrane Potential of an Undisturbed Cell.
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Changes in Membrane Potential (8-3)
• Stimuli alter membrane permeability to Na+ or K+
• Or alter activity of the exchange pump
• Types include:
• Cellular exposure to chemicals
• Mechanical pressure
• Temperature changes
• Changes in the ECF ion concentration
• Result is opening of a gated channel
• Increasing the movement of ions across the membrane
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Changes in Membrane Potential (8-3)
• Opening of Na+ channels results in an influx of Na+
• Moving the membrane toward 0 mV, a shift called
depolarization
• Opening of K+ channels results in an efflux of K+
• Moving the membrane further away from 0 mV, a shift
called hyperpolarization
• Return to resting from depolarization: repolarizing
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Graded Potentials (8-3)
• Local changes in the membrane that fade over
distance
• All cells experience graded potentials when
stimulated
• And can result in the activation of smaller cells
• Graded potentials by themselves cannot trigger
activation of large neurons and muscle fibers
• Referred to as having excitable membranes
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Action Potentials (8-3)
• A change in the membrane that travels the entire
length of neurons
• A nerve impulse
• If a combination of graded potentials causes the
membrane to reach a critical point of
depolarization, it is called the threshold
• Then an action potential will occur
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Action Potentials (8-3)
• Are all-or-none and will propagate down the
length of the neuron
• From the time the voltage-gated channels open
until repolarization is finished:
• The membrane cannot respond to further stimulation
• This period of time is the refractory period
• And limits the rate of response by neurons
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A graded depolarization
brings an area of excitable membrane
to threshold (–60 mV).
Voltage-gated sodium channels open and sodium ions move into the cell. The membrane potential rises to +30 mV.
Potassium channels close, and both sodium
and potassium channels return to their
normal states.
Sodium channels close, voltage-gated potassium channels
open, and potassium ions move out of the cell. Repolarization begins.
D E P O L A R I Z A T I O N R E P O L A R I Z A T I O N
Restingpotential
Threshold
During the refractory period, the membrane cannot respond to further stimulation.
Axon hillock
First part of axon toreach threshold
+30
0
–40
–60–70
Mem
bra
ne
po
ten
tial
(m
V)
REFRACTORY PERIOD
Time (msec)0 21
2
3
41
The Generation of an Action PotentialSPOTLIGHTFIGURE 8-8
Closing of Potassium Channels
Inactivation of SodiumChannels and Activationof Potassium Channels
Activation of SodiumChannels and RapidDepolarization
Depolarization toThresholdResting
PotentialRestingPotential
4321
–60 mV +10 mV+30 mV
–70 mV –90 mV –70 mV
Localcurrent
The axon membranecontains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential.
The stimulus that begins an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold.
When the voltage-gated sodium channels open, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from –60 mVto a positive value.
As the membrane potential approaches+30 mV, voltage-gated sodium channels close. This step coincides with the opening of voltage-gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolariza-tion now begins.
The voltage-gated sodium channels remain inactivated until the membrane has repolar-ized to near threshold levels. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about –70 mV). Until all have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization.
As the voltage-gated potassium channels close, the membrane potential returns to normal resting levels. The action potential is now over, and the membrane is once again at the resting potential.
= Sodium ion= Potassium ion
Figure 8-8 The Generation of an Action Potential
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Sodium channels close, voltage-gated potassium channels open,
and potassium ions move out of thecell. Repolarization begins.
D E P O L A R I Z AT I O N R E P O L A R I Z AT I O N
Restingpotential
Threshold
Voltage-gated sodiumchannels open andsodium ions move intothe cell. The membranepotential rises to +30mV.
Potassium channelsclose, and both sodium
and potassium chan-nels return to their
normal states.
A gradeddepolarization bringsan area of excitable
membrane to thresh-old (–60 mV).
During the refractory period,the membrane cannotrespond to further stimulation.
REFRACTORY PERIOD
Time (msec)
Mem
bra
ne
po
ten
tial
(m
V)
+30
0
–40
–60–70 1
2
3
4
0 1 2
Figure 8-8 The Generation of an Action Potential
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Figure 8-8 The Generation of an Action Potential
The axon membrane contains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential.
= Sodium ion= Potassium ion
–70 mV
Resting Potential
The stimulus that begins an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold.
Localcurrent
–60 mV
Depolarization to Threshold
When the voltage-gated sodium channels open, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from –60 mV to a positive value.
Activation of SodiumChannels and RapidDepolarization
+10 mV
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Figure 8-8 The Generation of an Action Potential
RestingPotential
+30 mV–90 mV
–70 mV
Inactivation of SodiumChannels and Activation of Potassium Channels
As the membrane potential approaches+30 mV, voltage-gated sodium channels close. This step coincides with the opening of voltage-gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolariza-tion now begins.
Closing of Potas-sium Channels
The voltage-gated sodium channels remain inactivated until the membrane has repolar-ized to near threshold levels. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about –70 mV). Until all have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization.
As the voltage-gatedpotassium channelsclose, the mem-brane potential re-turns to normal rest-ing levels. Theaction potential isnow over, and themembrane is onceagain at the restingpotential.
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Propagation of an Action Potential (8-3)
• Occurs when local changes in the membrane in
one site: • Result in the activation of voltage-gated channels in the next
adjacent site of the membrane
• This causes a wave of membrane potential
changes
• Continuous propagation • Occurs in unmyelinated fibers and is relatively slow
• Saltatory propagation • Is in myelinated axons and is faster
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Action potential propagation along anunmyelinated axon
Action potential propagation along amyelinated axon
Stimulusdepolarizes
membrane tothreshold
Stimulusdepolarizes
membrane tothreshold
EXTRACELLULAR FLUID
Plasma membrane CYTOSOL CYTOSOLPlasma membrane
EXTRACELLULAR FLUID
Repolarization(refractory period)
Repolarization(refractory period)
MyelinatedInternode Internode Internode
Myelinated Myelinated
MyelinatedMyelinatedMyelinatedInternode Internode Internode
InternodeInternodeInternodeMyelinated Myelinated Myelinated
Local current
Local current
Figure 8-9 The Propagation of Action Potentials over Unmyelinated and Myelinated Axons.
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Checkpoint (8-3)
9. What effect would a chemical that blocks the voltage-gated
sodium channels in a neuron's plasma membrane have on the
neuron's ability to depolarize?
10. What effect would decreasing the concentration of extracellular
potassium have on the membrane potential of a neuron?
11. List the steps involved in the generation and propagation of an
action potential.
12. Two axons are tested for propagation velocities. One carries
action potentials at 50 meters per second, the other at 1 meter
per second. Which axon is myelinated?
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The Synapse (8-4)
• A junction between a neuron and another cell
• Occurs because of chemical messengers called
neurotransmitters
• Communication happens in one direction only
• Between a neuron and another cell type is a neuroeffector
junction
• Such as the neuromuscular junction or neuroglandular junction
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A Synapse between Two Neurons (8-4)
• Occurs:
• Between the axon terminals of the presynaptic neuron
• Across the synaptic cleft
• To the dendrite or cell body of the postsynaptic neuron
• Neurotransmitters
• Stored in vesicles of the axon terminals
• Released into the cleft and bind to receptors on the
postsynaptic membrane
PLAYPLAY ANIMATION Neurophysiology: Synapse
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Axon ofpresynaptic cell
Axonterminal
Mitochondrion
Synapticvesicles
Presynapticmembrane
Postsynapticmembrane
Synapticcleft
Figure 8-10 The Structure of a Typical Synapse.
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The Neurotransmitter ACh (8-4)
• Activates cholinergic synapses in four steps
1. Action potential arrives at the axon terminal
2. ACh is released and diffuses across synaptic cleft
3. ACh binds to receptors and triggers depolarization of
the postsynaptic membrane
4. ACh is removed by AChE (acetylcholinesterase)
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Figure 8-11 The Events at a Cholinergic Synapse.
An action potential arrives anddepolarizes the axon terminal
Presynapticneuron
Synapticvesicles
Action potentialEXTRACELLULAR
FLUIDAxonterminal
AChE
POSTSYNAPTICNEURON
Extracellular Ca2+ enters the axonterminal, triggering the exocytosis of ACh
Ca2+
Synaptic cleftCa2+
ACh
Chemically regulatedsodium ion channels
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Figure 8-11 The Events at a Cholinergic Synapse.
ACh binds to receptors and depolarizesthe postsynaptic membrane
Initiation ofaction potentialif threshold is
reached
ACh is removed by AChE
Propagation ofaction potential
(if generated)
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Table 8-1 The Sequence of Events at a Typical Cholinergic Synapse
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Other Important Neurotransmitters (8-4)
• Norepinephrine (NE)
• In the brain and part of the ANS, is found in adrenergic
synapses
• Dopamine, GABA, and serotonin
• Are CNS neurotransmitters
• At least 50 less-understood neurotransmitters
• NO and CO
• Are gases that act as neurotransmitters
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Excitatory vs. Inhibitory Synapses (8-4)
• Usually, ACh and NE trigger depolarization
• An excitatory response
• With the potential of reaching threshold
• Usually, dopamine, GABA, and serotonin trigger
hyperpolarization
• An inhibitory response
• Making it farther from threshold
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Neuronal Pools (8-4)
• Multiple presynaptic neurons can synapse with
one postsynaptic neuron
• If they all release excitatory neurotransmitters:
• Then an action potential can be triggered
• If they all release an inhibitory neurotransmitter:
• Then no action potential can occur
• If half release excitatory and half inhibitory neurotransmitters:
• They cancel, resulting in no action
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Neuronal Pools (8-4)
• A term that describes the complex grouping of
neural pathways or circuits
• Divergence
• Is a pathway that spreads information from one neuron
to multiple neurons
• Convergence
• Is when several neurons synapse with a single
postsynaptic neuron
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Divergence Convergence
A mechanism forspreading stimulation tomultiple neurons orneuronal pools in theCNS
A mechanism for providinginput to a single neuron frommultiple sources
Figure 8-12 Two Common Types of Neuronal Pools.
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Checkpoint (8-4)
13. Describe the general structure of a synapse.
14. What effect would blocking calcium channels at
a cholinergic synapse have on synapse
function?
15. What type of neural circuit permits both
conscious and subconscious control of the same
motor neurons?
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The Meninges (8-5)
• The neural tissue in the CNS is protected by
three layers of specialized membranes
1. Dura mater
2. Arachnoid
3. Pia mater
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The Dura Mater (8-5)
• Is the outer, very tough covering
• The dura mater has two layers, with the outer layer
fused to the periosteum of the skull
• Dural folds contain large veins, the dural sinuses
• In the spinal cord the dura mater is separated from the
bone by the epidural space
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The Arachnoid
• Is separated from the dura mater by the subdural
space
• That contains a little lymphatic fluid
• Below the epithelial layer is arachnoid space
• Created by a web of collagen fibers
• Contains cerebrospinal fluid
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The Pia Mater
• Is the innermost layer
• Firmly bound to the neural tissue underneath
• Highly vascularized
• Providing needed oxygen and nutrients
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Checkpoint (8-5)
16. Identify the three meninges surrounding the CNS.
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Spinal Cord Structure (8-6)
• The major neural pathway between the brain and
the PNS
• Can also act as an integrator in the spinal reflexes
• Involving the 31 pairs of spinal nerves
• Consistent in diameter except for the cervical
enlargement and lumbar enlargement
• Where numerous nerves supply upper and lower limbs
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Spinal Cord Structure (8-6)
• Central canal
• A narrow passage containing cerebrospinal fluid
• Surface of the spinal cord is indented by the:
• Posterior median sulcus
• Deeper anterior median fissure
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31 Spinal Segments (8-6)
• Identified by a letter and number relating to the
nearby vertebrae
• Each has a pair of dorsal root ganglia
• Containing the cell bodies of sensory neurons with
axons in dorsal root
• Ventral roots contain motor neuron axons
• Roots are contained in one spinal nerve
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Figure 8-14a Gross Anatomy of the Spinal Cord.
Cervicalenlargement
Posteriormedian sulcus
Lumbarenlargement
Inferior tip of spinal cord
Cauda equina
Cervical spinalnerves
Thoracicspinal
nerves
Lumbarspinal
nerves
Sacral spinalnerves
Coccygealnerve (Co1)
In this superficial view of theadult spinal cord, thedesignations to the left identifythe spiral nerves.
C1C2C3C4C5C6C7C8
T1T2T3T4T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L3
L4
L5
S5S5
S1S1
S2S2
S3S3
S4S4
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Figure 8-14b Gross Anatomy of the Spinal Cord.
This cross section through thecervical region of the spinal cordshows some prominent features andthe arrangement of gray matter andwhite matter.
C3
Dorsal root
Dorsal rootganglion
Centralcanal
Spinalnerve
Ventralroot
Posterior median sulcus
White matter
Gray matter
Anterior median fissure
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Sectional Anatomy of the Spinal Cord (8-6)
• The central gray matter is made up of glial cells
and nerve cell bodies
• Projections of gray matter are called horns
• Which extend out into the white matter
• White matter is myelinated and unmyelinated
axons
• The location of cell bodies in specific nuclei of the
gray matter relate to their function
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Sectional Anatomy of the Spinal Cord (8-6)
• Posterior gray horns are somatic and visceral
sensory nuclei
• Lateral gray horns are visceral (ANS) motor nuclei
• The anterior gray horns are somatic motor nuclei
• White matter can be organized into three columns
• Which contain either ascending tracts to the brain, or
descending tracts from the brain to the PNS
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Posterior white column
Dorsal root
ganglion
Lateralwhite
column
Posteriorgray horn
Lateralgray horn
Anteriorgray
horn
Posteriormedian sulcusPosterior graycommissure
Somatic
VisceralVisceralSomatic
Functional Organizationof Gray MatterThe cell bodies of neurons in thegray matter of the spinal cord areorganized into functional groupscalled nuclei.
Sensory nuclei
Motor nuclei
Ventral rootAnterior gray commissureAnterior white commissureAnterior median fissure
Anterior white column
The left half of this sectional view shows important anatomical landmarks, including thethree columns of white matter. The right half indicates the functional organization of thenuclei in the anterior, lateral, and posterior gray horns.
Posteriormedian sulcus
POSTERIOR Structural Organizationof Gray Matter
The projections of gray mattertoward the outer surface of thespinal cord are called horns.
Posterior gray horn
Lateral gray horn
Anterior gray horn
Dorsalroot
Dorsal rootganglion
Ventral root
Posterior graycommissure
Dura mater
Arachnoid mater(broken)
Central canalAnterior graycommissure
Anterior medianfissure
Pia mater
A micrograph of a section through the spinal cord, showingmajor landmarks in and surrounding the cord.
ANTERIOR
Figure 8-15 Sectional Anatomy of the Spinal Cord.
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Figure 8-15a Sectional Anatomy of the Spinal Cord.
Posterior white column Posteriormedian sulcus
Posterior graycommissure
Posteriorgray horn
Dorsal rootganglion
Lateralwhite
column
Lateralgray horn
Anteriorgray
horn
Somatic
Visceral
Visceral
Somatic
Functional Organizationof Gray Matter
The cell bodies of neurons in thegray matter of the spinal cord areorganized into functional groupscalled nuclei.
Sensory nuclei
Motor nuclei
Ventral rootAnterior gray commissureAnterior white commissureAnterior median fissure
Anterior white column
The left half of this sectional view shows important anatomical landmarks, including thethree columns of white matter. The right half indicates the functional organization of thenuclei in the anterior, lateral, and posterior gray horns.
© 2013 Pearson Education, Inc.
Figure 8-15b Sectional Anatomy of the Spinal Cord.
A micrograph of a section through the spinal cord, showingmajor landmarks in and surrounding the cord.
Pia mater
Anterior medianfissure
Anterior graycommissure
Central canal
Arachnoid mater(broken)
Dura mater
Posterior graycommissure
POSTERIOR
ANTERIOR
Posteriormedian sulcus
Dorsalroot
Dorsal rootganglionVentral root
Structural Organizationof Gray Matter
Posterior gray horn
Lateral gray horn
Anterior gray horn
The projections of gray mattertoward the outer surface of thespinal cord are called horns.
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Checkpoint (8-6)
17. Damage to which root of a spinal nerve would
interfere with motor function?
18. A person with polio has lost the use of his leg
muscles. In which areas of his spinal cord could
you locate virus-infected neurons?
19. Why are spinal nerves also called mixed nerves?
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Six Major Regions of the Brain (8-7)
1. The cerebrum
2. The diencephalon
3. The midbrain
4. The pons
5. The medulla oblongata
6. The cerebellum
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Major Structures of the Brain (8-7)
• The cerebrum
• Is divided into paired cerebral hemispheres
• Deep to the cerebrum is the diencephalon
• Which is divided into the thalamus, the hypothalamus,
and the epithalamus
• The brain stem
• Contains the midbrain, pons, and medulla oblongata
• The cerebellum
• Is the most inferior/posterior part
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Figure 8-16a The Brain.
Longitudinal fissure
Cerebral veins and arteriesbelow arachnoid mater
Right cerebral hemisphereLeft cerebral hemisphere
CEREBRUM
CEREBELLUM
ANTERIOR
POSTERIOR
Superior view
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Figure 8-16b The Brain.
Precentral gyrus
Frontal lobe of leftcerebral hemisphere
Lateral sulcus
Temporal lobe
PONS
Central sulcus
Postcentralgyrus
Parietallobe
Occipitallobe
CEREBELLUM
MEDULLA OBLONGATA Lateral view
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Figure 8-16c The Brain.
Corpuscallosum
Precentralgyrus
Centralsulcus
Postcentralgyrus
ThalamusHypothalamusPineal gland(part of epithalamus)
Parieto-occipital sulcus
CEREBELLUM
Sagittal sectionMEDULLA OBLONGATA PONSMIDBRAIN
Brain stem
Temporal lobe
Fornix
Frontal lobe
Opticchiasm
Mamillary body
DIENCEPHALON
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The Ventricles of the Brain (8-7)
• Filled with cerebrospinal fluid and lined with
ependymal cells
• The two lateral ventricles within each cerebral
hemisphere drain through the:
• Interventricular foramen into the:
• Third ventricle in the diencephalon, which drains
through the cerebral aqueduct into the:
• Fourth ventricle, which drains into the central canal
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Cerebralhemispheres
PonsMedulla oblongata
Spinal cord
A lateral view of the ventriclesCentral canal
Lateralventricles
Interventricularforamen
Thirdventricle
Cerebralaqueduct
Fourthventricle
Cerebral hemispheres
Central canal Cerebellum
An anterior view of the ventricles
Ventricles ofthe Brain
Figure 8-17 The Ventricles of the Brain.
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Cerebrospinal Fluid (8-7)
• CSF
• Surrounds and bathes the exposed surfaces of the CNS
• Floats the brain
• Transports nutrients, chemicals, and wastes
• Is produced by the choroid plexus
• Continually secreted and replaced three times per day
• Circulation from the fourth ventricle into the
subarachnoid space into the dural sinuses
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Figure 8-18a The Formation and Circulation of Cerebrospinal Fluid.
A sagittal section of the CNS. Cerebrospinal fluid, formed in the choroid plexus, circulates along the routes indicated by the red arrows.
Spinal cord
Central canal
Superiorsagittalsinus
ArachnoidgranulationsExtension of choroid
plexus intolateral ventricle
Choroid plexusof third ventricle
CerebralaqueductLateral aperture
Choroid plexus offourth ventricle
Median aperture
Arachnoid mater
Subarachnoid space
Dura mater
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Figure 8-18b The Formation and Circulation of Cerebrospinal Fluid.
The relation-ship of the arachnoid granulations and dura mater.
Piamater
Subarachnoidspace
Arachnoidmater
Subduralspace
Dura mater(inner layer)
Fluidmovement
Arachnoidgranulation
Dura mater(outer layer)
CraniumSuperior
sagittal sinus
Cerebralcortex
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The Cerebrum (8-7)
• Contains an outer gray matter called the cerebral
cortex
• Deep gray matter in the cerebral nuclei and white matter of
myelinated axons beneath the cortex and around the nuclei
• The surface of the cerebrum
• Folds into gyri
• Separated by depressions called sulci or deeper grooves
called fissures
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The Cerebral Hemispheres (8-7)
• Are separated by the longitudinal fissure
• The central sulcus
• Extends laterally from the longitudinal fissure
• The frontal lobe
• Is anterior to the central sulcus
• Is bordered inferiorly by the lateral sulcus
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The Cerebral Hemispheres (8-7)
• The temporal lobe
• Inferior to the lateral sulcus
• Overlaps the insula
• The parietal lobe
• Extends between the central sulcus and the parieto-
occipital sulcus
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The Cerebral Hemispheres (8-7)
• The occipital lobe
• Located most posteriorly
• The lobes are named for the cranial bone above it
• Each lobe has sensory regions and motor regions
• Each hemisphere sends and receives information
from the opposite side of the body
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Motor and Sensory Areas of the Cortex (8-7)
• Are divided by the central sulcus
• The precentral gyrus of the frontal lobe
• Contains the primary motor cortex
• The postcentral gyrus of the parietal lobe
• Contains the primary sensory cortex
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Motor and Sensory Areas of Cortex (8-7)
• The visual cortex is in the occipital lobe
• The gustatory, auditory, and olfactory cortexes
are in the temporal lobe
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Association Areas (8-7)
• Interpret incoming information
• Coordinate a motor response, integrating the
sensory and motor cortexes
• The somatic sensory association area
• Helps to recognize touch
• The somatic motor association area
• Is responsible for coordinating movement
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Primary motor cortex(precentral gyrus)
Somatic motor associationarea (premotor cortex)
FRONTAL LOBE
Prefrontal cortex
Gustatory cortexInsula
Lateral sulcus
Olfactory cortex
TEMPORAL LOBE
Auditory cortex
Auditoryassociation area
Visual cortexOCCIPITAL LOBE
Visual associationarea
Somatic sensoryassociation area
PARIETAL LOBE
Primary sensory cortex(postcentral gyrus)
Central sulcus
Figure 8-19 The Surface of the Cerebral Hemispheres.
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Cortical Connections (8-7)
• Regions of the cortex are linked by the deeper
white matter
• The left and right hemispheres are linked across
the corpus callosum
• Other axons link the cortex with:
• The diencephalon, brain stem, cerebellum, and spinal
cord
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Higher-Order Centers (8-7)
• Integrative areas, usually only in the left
hemisphere
• The general interpretive area or Wernicke's area
• Integrates sensory information to form visual and auditory
memory
• The speech center or Broca's area
• Regulates breathing and vocalization, the motor skills
needed for speaking
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The Prefrontal Cortex (8-7)
• In the frontal lobe
• Coordinates information from the entire cortex
• Skills such as:
• Predicting time lines
• Making judgments
• Feelings such as:
• Frustration, tension, and anxiety
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Hemispheric Lateralization (8-7)
• The concept that different brain functions can and
do occur on one side of the brain
• The left hemisphere tends to be involved in language
skills, analytical tasks, and logic
• The right hemisphere tends to be involved in analyzing
sensory input and relating it to the body, as well as
analyzing emotional content
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General interpretivecenter (language and
mathematical calculation)
Auditory cortex(right ear)
Writing
Speech center
Prefrontalcortex
LEFT HAND RIGHT HAND
Prefrontalcortex
Anterior commissure
Analysis by touch
Auditory cortex(left ear)
Spatial visualizationand analysis
Visual cortex(left visual field)
Visual cortex(right visual field)
CORPUSCALLOSUM
RIGHTHEMISPHERE
LEFTHEMISPHERE
Figure 8-20 Hemispheric Lateralization.
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The Electroencephalogram (8-7)
• EEG
• A printed record of brain wave activity
• Can be interpreted to diagnose brain disorders
• More modern techniques
• Brain imaging, using the PET scan and MRIs, has
allowed extensive "mapping" of the brain's functional
areas
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Patient being wiredfor EEG monitoring
Alpha waves are characteristic of normal resting adults
Beta waves typicallyaccompany intense concentration
Theta waves are seen in children and in frustrated adults
Delta waves occur in deep sleep and in certain pathological conditions
0 1 2 3 4Seconds
Figure 8-21 Brain Waves.
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Memory (8-7)
• Fact memory
• The recall of bits of information
• Skill memory
• Learned motor skill that can become incorporated into unconscious
memory
• Short-term memory
• Doesn't last long unless rehearsed
• Converting into long-term memory through memory consolidation
• Long-term memory
• Remains for long periods, sometimes an entire lifetime
• Amnesia
• Memory loss as a result of disease or trauma
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The Basal Nuclei (8-7)
• Masses of gray matter
• Caudate nucleus
• Lies anterior to the lentiform nucleus
• Which contains the medial globus pallidus and the lateral
putamen
• Inferior to the caudate and lentiform nuclei is the amygdaloid body
or amygdala
• Basal nuclei
• Subconscious control of skeletal muscle tone
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Lateral view of a transparent brain, showing the relative positions of the basal nuclei
Lentiform nucleusThalamusTail of caudatenucleus
Amygdaloidbody
Head of caudatenucleus
Head ofcaudatenucleus Corpus
callosumLateral ventricle Insula
Tip of lateralventricle
AmygdaloidbodyGlobus pallidus
PutamenLentiformnucleus
Frontal section
Figure 8-22 The Basal Nuclei.
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The Limbic System (8-7)
• Includes the olfactory cortex, basal nuclei, gyri, and
tracts between the cerebrum and diencephalon
• A functional grouping, rather than an anatomical one
• Establishes the emotional states
• Links the conscious with the unconscious
• Aids in long-term memory with help of the
hippocampus
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Cingulate gyrus
Corpus callosum
Thalamic nuclei
Hypothalamicnuclei
Olfactory tractAmygdaloid body
Hippocampus
Fornix
Mamillary body
Figure 8-23 The Limbic System.
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The Diencephalon (8-7)
• Contains switching and relay centers
• Centers integrate conscious and unconscious sensory
information and motor commands
• Surround third ventricle
• Three components
1. Epithalamus
2. Thalamus
3. Hypothalamus
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The Epithalamus (8-7)
• Lies superior to the third ventricle and forms the
roof of the diencephalon
• The anterior part contains choroid plexus
• The posterior part contains the pineal gland that
is endocrine and secretes melatonin
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The Thalamus (8-7)
• The left and right thalamus are separated by the
third ventricle
• The final relay point for sensory information
• Only a small part of this input is sent on to the
primary sensory cortex
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The Hypothalamus (8-7)
• Lies inferior to the third ventricle
• The subconscious control of skeletal muscle
contractions is associated with strong emotion
• Adjusts the pons and medulla functions
• Coordinates the nervous and endocrine systems
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The Hypothalamus (8-7)
• Secretes hormones
• Produces sensations of thirst and hunger
• Coordinates voluntary and ANS function
• Regulates body temperature
• Coordinates daily cycles
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The Midbrain (8-7)
• Contains various nuclei
• Two pairs involved in visual and auditory processing, the colliculi
• Contains motor nuclei for cranial nerves III and IV
• Cerebral peduncles contain descending fibers
• Reticular formation is a network of nuclei related to the
state of wakefulness
• The substantia nigra influence muscle tone
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The Pons (8-7)
• Links the cerebellum with the midbrain,
diencephalon, cerebrum, and spinal cord
• Contains sensory and motor nuclei for cranial
nerves V, VI, VII, and VIII
• Other nuclei influence rate and depth of respiration
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The Cerebellum (8-7)
• An automatic processing center
• Which adjusts postural muscles to maintain balance
• Programs and fine-tunes movements
• The cerebellar peduncles
• Are tracts that link the cerebral cortex, basal nuclei, and brain stem
• Ataxia
• Is disturbance of coordination
• Can be caused by damage to the cerebellum
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The Medulla Oblongata (8-7)
• Connects the brain with the spinal cord
• Contains sensory and motor nuclei for cranial nerves VIII,
IX, X, XI, and XII
• Contains reflex centers
• Cardiovascular centers
• Adjust heart rate and arteriolar diameter
• Respiratory rhythmicity centers
• Regulate respiratory rate
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Figure 8-24a The Diencephalon and Brain Stem.
Cerebralpeduncle
Optic tract
Cranialnerves
ThalamusDiencephalon
Thalamic nuclei
MidbrainSuperior colliculusInferior colliculus
Cerebellar peduncles
Medullaoblongata
Spinalcord
Lateral view
Spinalnerve C2
Spinalnerve C1
N XIIN XIN X
N IX
N IIN III
N V
N IV
N VIN VII
N VIII
Pons
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Figure 8-24b The Diencephalon and Brain Stem.
N IV
Choroid plexusThalamusThird ventriclePineal gland
Corpora quadrigeminaSuperior colliculi
Inferior colliculi
Cerebral peduncle
Cerebellar peduncles
Posterior view
Dorsal rootsof spinal nerves
C1 and C2
Choroid plexus in roofof fourth ventricle
© 2013 Pearson Education, Inc.
Checkpoint (8-7)
20. Describe one major function of each of the six regions of
the brain.
21. The pituitary gland links the nervous and endocrine
systems. To which portion of the diencephalon is it
attached?
22. How would decreased diffusion across the arachnoid
granulations affect the volume of cerebrospinal fluid in the
ventricles?
23. Mary suffers a head injury that damages her primary
motor cortex. Where is this area located?
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Checkpoint (8-7)
24. What senses would be affected by damage to the
temporal lobes of the cerebrum?
25. The thalamus acts as a relay point for all but what type of
sensory information?
26. Changes in body temperature stimulate which area of the
diencephalon?
27. The medulla oblongata is one of the smallest sections of
the brain. Why can damage to it cause death, whereas
similar damage in the cerebrum might go unnoticed?
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Peripheral Nervous System (8-8)
• Links the CNS to the rest of the body through
peripheral nerves
• They include the cranial nerves and the spinal
nerves
• The cell bodies of sensory and motor neurons are
contained in the ganglia
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The Cranial Nerves (8-8)
• 12 pairs, noted as Roman numerals I through XII
• Some are:
• Only motor pathways
• Only sensory pathways
• Mixed having both sensory and motor neurons
• Often remembered with a mnemonic
• "Oh, Once One Takes The Anatomy Final, Very Good
Vacations Are Heavenly"
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The Cranial Nerves (8-8)
• The olfactory nerves (N I)
• Are connected to the cerebrum
• Carry information concerning the sense of smell
• The optic nerves (N II)
• Carry visual information from the eyes, through the
optic foramina of the orbits to the optic chiasm
• Continue as the optic tracts to the nuclei of the thalamus
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The Cranial Nerves (8-8)
• The oculomotor nerves (N III)
• Motor only, arising in the midbrain
• Innervate four of six extrinsic eye muscles and the
intrinsic eye muscles that control the size of the pupil
• The trochlear nerves (N IV)
• Smallest, also arise in the midbrain
• Innervate the superior oblique extrinsic muscles of the
eyes
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The Cranial Nerves (8-8)
• The trigeminal nerves (N V) • Have nuclei in the pons, are the largest cranial nerves
• Have three branches
1. The ophthalmic
• From the orbit, sinuses, nasal cavity, skin of
forehead, nose, and eyes
2. The maxillary
• From the lower eyelid, upper lip, cheek, nose, upper
gums, and teeth
• The mandibular
• From salivary glands and tongue
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The Cranial Nerves (8-8)
• The abducens nerves (N VI)
• Innervate only the lateral rectus extrinsic eye muscle,
with the nucleus in the pons
• The facial nerves (N VII)
• Mixed, and emerge from the pons
• Sensory fibers monitor proprioception in the face
• Motor fibers provide facial expressions; control tear and
salivary glands
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The Cranial Nerves (8-8)
• The vestibulocochlear nerves (N VIII)
• Respond to sensory receptors in the inner ear
• There are two components
1. The vestibular nerve
• Conveys information about balance and position
2. The cochlear nerve
• Responds to sound waves for the sense of hearing
• Their nuclei are in the pons and medulla oblongata
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The Cranial Nerves (8-8)
• The glossopharyngeal nerves (N IX)
• Mixed nerves innervating the tongue and pharynx
• Their nuclei are in the medulla oblongata
• The sensory portion monitors taste on the posterior third
of the tongue and monitors BP and blood gases
• The motor portion controls pharyngeal muscles used in
swallowing, and fibers to salivary glands
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The Cranial Nerves (8-8)
• The vagus nerves (N X)
• Have sensory input vital to autonomic control of the
viscera
• Motor control includes the soft palate, pharynx, and
esophagus
• Are a major pathway for ANS output to cardiac muscle,
smooth muscle, and digestive glands
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The Cranial Nerves (8-8)
• The accessory nerves (N XI)
• Have fibers that originate in the medulla oblongata
• Also in the lateral gray horns of the first five cervical
segments of the spinal cord
• The hypoglossal nerves (N XII)
• Provide voluntary motor control over the tongue
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Mamillarybody
Basilarartery
Olfactory bulb, terminationof olfactory nerve (I)
Olfactory tract
Optic chiasmOptic nerve (II)
Infundibulum
Oculomotor nerve(III)
Trochlear nerve(IV)
Trigeminal nerve(V)
Abducens nerve(VI)
Facial nerve (VII)
Vestibulocochlearnerve (VIII)
Glossopharyngeal nerve (IX)
Vagus nerve (X)Hypoglossal nerve
(XII)Accessory nerve (XI)
Diagrammatic view showing the attachment of the 12 pairs of cranial nerves
Spinal cordMedulla
oblongataCerebellum
Inferior view of the brain
Vertebral artery
Pons
Figure 8-25 The Cranial Nerves.
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Table 8-2 The Cranial Nerves
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The Spinal Nerves (8-8)
• Found in 31 pairs grouped according to the region
of the vertebral column
• 8 pairs of cervical nerves, C1–C8
• 12 pairs of thoracic nerves, T1–T12
• 5 pairs of lumbar nerves, L1–L5
• 5 pairs of sacral nerves, S1–S5
• 1 pair of coccygeal nerves, Co1
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Nerve Plexuses (8-8)
• The origin of major nerve trunks of the PNS
• The cervical plexus
• Innervates the muscles of the head and neck and the
diaphragm
• The brachial plexus
• Innervates the shoulder girdle and upper limb
• The lumbar plexus and the sacral plexus
• Innervate the pelvic girdle and lower limb
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Figure 8-26 Peripheral Nerves and Nerve Plexuses.
Phrenic nerve (extends to the diaphragm)
Axillary nerve
Musculocutaneousnerve
Radial nerve
Ulnar nerve Median nerve
Femoral nerve Obturator nerve
Gluteal nerves
Saphenous nerve
Sacralplexus
Lumbarplexus
Brachialplexus
Cervicalplexus
C1
Sciatic nerve
C2C3C4C5C6C7C8T1T2T3T4T5T6T7T8T9
T10T11T12
L1
L2
L3L4L5S1
S2S3S4S5
Co1
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Dermatome (8-8)
• A clinically important area monitored by a specific
spinal nerve
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C2–C3
C2
C2–C3
N V
C3
C4
C3
C5C4
C5
C6
C7C6
C8
C8
C7
T1T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
T2
T3
T4T5T6T7T8T9T10T11
T12
T2
T2
T1
T1
L1
L1L2
L2
L3L4L5
L1
L2
L3
L4
L5 L3
S2
S1 L5
S5
SS4 3
S2
S1
L4
ANTERIOR POSTERIOR
Figure 8-27 Dermatomes.
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Table 8-3 Nerve Plexuses and Major Nerves
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Checkpoint (8-8)
28. What signs would you associate with damage to the
abducens nerve (N VI)?
29. John is having trouble moving his tongue. His physician
tells him it is due to pressure on a cranial nerve. Which
cranial nerve is involved?
30. Injury to which nerve plexus would interfere with the
ability to breathe?
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Reflexes (8-9)
• Rapid, automatic, unlearned motor response to a stimulus
• Usually removes or opposes the original stimulus
• Monosynaptic reflexes
• For example, the stretch reflex
• Which responds to muscle spindles, is the simplest with only
one synapse
• The best known stretch reflex is probably the knee jerk reflex
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Simple Reflexes (8-9)
• Are wired in a reflex arc
• A stimulus activates a sensory receptor
• An action potential travels down an afferent neuron
• Information processing occurs with the interneuron
• An action potential travels down an efferent neuron
• The effector organ responds
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Arrival ofstimulus andactivation ofreceptor
Activation of asensory neuron
Dorsalroot
Sensationrelayed to the brain by axon
collaterals
Informationprocessingin the CNS
REFLEXARC
ReceptorStimulusEffector
Response byeffector Ventral
root
Activation of amotor neuron
KEYSensoryneuron(stimulated)
ExcitatoryinterneuronMotor neuron(stimulated)
Figure 8-28 The Components of a Reflex Arc.
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Stretching of muscle tendonstimulates muscle spindles
Muscle spindle(stretch receptor)
SpinalCord
REFLEXARC
Contraction
Stretch
Activation of motorneuron produces reflex muscle contraction
Figure 8-29 A Stretch Reflex.
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Complex Reflexes (8-9)
• Polysynaptic reflexes
• With at least one interneuron
• Are slower than monosynaptic reflexes, but can activate
more than one effector
• Withdrawal reflexes
• Like the flexor reflex, move a body part away from the
stimulation
• Like touching a hot stove
• Reciprocal inhibition
• Blocks the flexor's antagonist
• To ensure that flexion is in no way interfered with
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Distribution within gray horns to other segments of the spinal cord
Painful stimulus Flexors
stimulated
Extensorsinhibited
KEYSensory neuron(stimulated)
Excitatoryinterneuron
Motor neuron(stimulated)
Motor neuron(inhibited)
Inhibitoryinterneuron
Figure 8-30 The Flexor Reflex, a Type of Withdrawal Reflex.
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Input to Modify Reflexes (8-9)
• Reflexes are automatic, but higher brain centers
can influence or modify them
• The Babinski sign
• Triggered by stroking an infant's sole, resulting in a
fanning of the toes
• As descending inhibitory synapses develop, an adult will
respond by curling the toes instead, called the plantar
reflex
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Checkpoint (8-9)
31. Define reflex.
32. Which common reflex do physicians use to test the
general condition of the spinal cord, peripheral nerves,
and muscles?
33. Why can polysynaptic reflexes produce more involved
responses than can monosynaptic reflexes?
34. After injuring his back lifting a sofa, Tom exhibits a
positive Babinski reflex. What does this imply about
Tom's injury?
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Sensory Pathways (8-10)
• Are ascending pathways
• Posterior column pathway
• Spinothalamic pathway
• Spinocerebellar pathway
• A sensory homunculus
• A mapping of the area of the cortex dedicated to the
number of sensory receptors, not the size of the body
area
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Sensory homunculus ofleft cerebral hemisphere
KEYAxon of first-order neuron
Second-orderneuronThird-orderneuron
Nucleus in medulla
oblongata
Nuclei inthalamus
MIDBRAIN
MEDULLA OBLONGATA
SPINAL CORD
Dorsal rootganglion
Fine-touch, pressure, vibration, and proprio-ception sensations from right side of body
Figure 8-31 The Posterior Column Pathway.
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Motor Pathways (8-10)
• Are descending pathways
• Corticospinal pathway
• Also called pyramidal system
• Medial and lateral pathways
• Also called extrapyramidal system
• A motor homunculus
• Represents the distribution of somatic and ANS motor
innervation
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Motor homunculus on primary motorcortex of left cerebral
hemisphereAxon of uppermotor neuron
Lower motorneuron
To skeletalmuscles
To skeletalmuscles
Motor nucleiof cranial
nerves
MIDBRAIN
MEDULLA OBLONGATA
Lateralcorticospinal
tract
To skeletalmuscles
Anterior corticospinal tract
KEY
SPINAL CORDMotor neuron in anterior gray horn
Motor nucleiof cranial
nerves
Figure 8-32 The Corticospinal Pathway.
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Table 8-4 Sensory and Motor Pathways
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Checkpoint (8-10)
35. As a result of pressure on her spinal cord, Jill cannot feel
touch or pressure on her legs. What sensory pathway is
being compressed?
36. The primary motor cortex of the right cerebral hemisphere
controls motor function on which side of the body?
37. An injury to the superior portion of the motor cortex
would affect the ability to control muscles of which parts
of the body?
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The Autonomic Nervous System (8-11)
• Unconscious adjustment of homeostatically essential
visceral responses
• Sympathetic division
• Parasympathetic division
• The somatic NS and ANS are anatomically different
• SNS: one neuron to skeletal muscle
• ANS: two neurons to cardiac and smooth muscle, glands, and fat
cells
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Two Neuron Pathways of the ANS (8-11)
• Preganglionic neuron
• Has cell body in spinal cord, synapses at the ganglion with the
postganglionic neuron
• In sympathetic division
• Preganglionic fibers are short
• Postganglionic fibers are long
• In parasympathetic division
• Preganglionic fibers are long
• Postganglionic fibers are "short"
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Upper motorneurons inPrimarymotorcortex
Somatic motor nuclei of brain stem
Skeletalmuscle
Lowermotor
neurons
BRAIN
Preganglionic neuronVisceral Effectors
Smoothmuscle
Glands
Cardiacmuscle
Adipocytes
Visceral motor nuclei inhypothalamus
BRAIN
Autonomicnuclei inbrain stem
SPINAL CORD
Autonomic nuclei in spinal cord
Preganglionicneuron
Autonomic nervous systemSomatic nervous system
Somatic motornuclei ofspinal cord
SPINALCORD
Skeletalmuscle
Autonomicganglia
Ganglionicneurons
Figure 8-33 The Organization of the Somatic and Autonomic Nervous Systems.
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Neurotransmitters at Specific Synapses (8-11)
• All synapses between pre- and postganglionic fibers:
• Are cholinergic (ACh) and excitatory
• Postganglionic parasympathetic synapses
• Are cholinergic
• Some are excitatory, some inhibitory, depending on the receptor
• Most postganglionic sympathetic synapses:
• Are adrenergic (NE) and usually excitatory
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The Sympathetic Division (8-11)
• Sympathetic chain
• Arises from spinal segments T1–L2
• The preganglionic fibers enter the sympathetic chain
ganglia just outside the spinal column
• Collateral ganglia are unpaired ganglia that receive
splanchnic nerves from the lower thoracic and upper
lumbar segments
• Postganglionic neurons innervate abdominopelvic cavity
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The Sympathetic Division (8-11)
• The adrenal medullae
• Are innervated by preganglionic fibers
• Are modified neural tissue that secrete E and NE into
capillaries, functioning like an endocrine gland
• The effect is nearly identical to that of the sympathetic
postganglionic stimulation of adrenergic synapses
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Eye
Salivaryglands
Heart
Lung
Liver andgallbladderStomach
Pancreas
Largeintestine
Spleen
Smallintestine
AdrenalmedullaKidney
Sympatheticchain ganglia
Postganglionic fibers to spinal
nerves(innervating skin,
blood vessels,sweat glands,arrector pili
muscles,adipose tissue)
Collateralganglion
Splanchnic nerve
Coll-ateral
ganglion
Splan-chnicnerves
Collateral ganglion
Cardiac andpulmonary plexuses
Cervicalsympathetic
ganglia
Spinal nerves
Spinal cord
Urinary bladderOvaryUterus ScrotumPenis
Sympathetic nerves
PONS
L2L2
T1 T1
Figure 8-34 The Sympathetic Division.
Ganglionic neuronsPreganglionic neurons
KEY
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The Sympathetic Division (8-11)
• Also called the "fight-or-flight" division
• Effects
• Increase in alertness, metabolic rate, sweating, heart
rate, blood flow to skeletal muscle
• Dilates the respiratory bronchioles and the pupils
• Blood flow to the digestive organs is decreased
• E and NE from the adrenal medullae support and
prolong the effect
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The Parasympathetic Division (8-11)
• Preganglionic neurons arise from the brain stem
and sacral spinal cord
• Include cranial nerves III, VII, IX, and X, the vagus,
a major parasympathetic nerve
• Ganglia very close to or within the target organ
• Preganglionic fibers of the sacral areas form the
pelvic nerves
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The Parasympathetic Division (8-11)
• Less divergence than in the sympathetic division,
so effects are more localized
• Also called "rest-and digest" division
• Effects
• Constriction of the pupils, increase in digestive secretions,
increase in digestive tract smooth muscle activity
• Stimulates urination and defecation
• Constricts bronchioles, decreases heart rate
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PONS
Terminal ganglionN III Lacrimal gland
Eye
Salivary glands
Terminal ganglionN VII
Terminal ganglion
Terminal ganglion
N IX
N X (Vagus) Heart
Lungs
Cardiac andpulmonaryplexuses
Liver and gallbladder
Stomach
SpleenPancreas
Large intestine
Small intestine
Rectum
Kidney
Urinary bladder
ScrotumPenisOvaryUterus
Spinalcord
Pelvicnerves
S2
S3
S4
Figure 8-35 The Parasympathetic Division.
KEYPreganglionic neuronsGanglionic neurons
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Dual Innervation (8-11)
• Refers to both divisions affecting the same organs
• Mostly have antagonistic effects
• Some organs are innervated by only one division
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Table 8-5 The Effects of the Sympathetic and Parasympathetic Divisions of the ANS on Various Body Structures(1 of 2)
© 2013 Pearson Education, Inc.
Table 8-5 The Effects of the Sympathetic and Parasympathetic Divisions of the ANS on Various Body Structures(2 of 2)
© 2013 Pearson Education, Inc.
Checkpoint (8-11)
38. While out for a brisk walk, Megan is suddenly confronted
by an angry dog. Which division of the ANS is responsible
for the physiological changes that occur as she turns and
runs from the animal?
39. Why is the parasympathetic division of the ANS
sometimes referred to as the anabolic system?
40. What effect would loss of sympathetic stimulation have on
the flow of air into the lungs?
41. What physiological changes would you expect in a
patient who is about to undergo a root canal procedure
and is quite anxious about it?
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Aging and the Nervous System (8-12)
• Common changes
• Reduction in brain size and weight and reduction in
number of neurons
• Reduction in blood flow to the brain
• Change in synaptic organization of the brain
• Increase in intracellular deposits and extracellular
plaques
• Senility can be a result of all these changes
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Checkpoint (8-12)
42. What is the major cause of age-related
shrinkage of the brain?
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The nervous system is closely integrated with other body systems. Every moment of your life, billions of neurons in your nervous system are exchanging information across trillions of synapses and performing the most complex integrative functions in the body. As part of this process, the nervous system monitors all other systems and issues commands that adjust their activities. However, the impact of these commands varies greatly from one system to another. The normal functions of the muscular system, for example, simply cannot be performed without instructions from the nervous system. By contrast, the cardiovascular system is relatively independent—the nervous system merely coordinates and adjusts cardiovascular activities to meet the circulatory demands of other systems. In the final analysis, the nervous system is like the conductor of an orchestra, directing the rhythm and balancing the performances of each section to produce a symphony, instead of simply a very loud noise.
The NERVOUS System
Provides sensations of touch, pressure, pain, vibration, and temperature; hair provides some protection and insulation for skull and brain; protects peripheral nerves
Provides calcium for neural function; protects brain and spinal cord
Facial muscles express emotional state; intrinsic laryngeal muscles permit communication; muscle spindles provide proprioceptive sensations
Controls contraction of arrector pili muscles and secretion of sweat glands
Controls skeletal muscle contractions that results in bone thickening and maintenance and determine bone position
Controls skeletal muscle contractions; coordinates respiratory and cardiovascular activities
SYSTEM INTEGRATORBody System Nervous System Nervous System Body System
Inte
gu
men
tary
Ske
leta
lM
usc
ula
r
Inte
gum
enta
ry(P
age
138)
Ske
leta
l(P
age
188)
Musc
ula
r(P
age
241)
Endocr
ine
(Pag
e 37
6)C
ard
iovasc
ula
r(P
age
467)
Lym
phati
c(P
age
500)
Resp
irato
ry(P
age
532)
Dig
est
ive
(Pag
e 57
2)U
rinary
(Pag
e 63
7)R
epro
duct
ive
(Pag
e 67
1)
Figure 8-36
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Checkpoint (8-13)
43. Identify the relationships between the nervous
system and the body systems studied so
far.