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Copyright © 2010 Pearson Education, Inc.
THE NERVOUS SYSTEM: PART C
Copyright © 2010 Pearson Education, Inc.
Central nervous system (CNS) Peripheral nervous system (PNS)
Motor (efferent) divisionSensory (afferent)division
Somatic nervoussystem
Autonomic nervoussystem (ANS)
Sympatheticdivision
Parasympatheticdivision
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Spinal Cord
• Location
• Begins at the foramen magnum
• Ends at L1 vertebra
• Functions
• Provides two-way communication to and from the brain
• Contains spinal reflex centers
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Spinal Cord
• Spinal nerves
• 31 pairs
• Cauda equina
• The collection of nerve roots at the inferior end of the vertebral canal
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• Bone
• Meninges
• CSF
Spinal Cord Protection
Copyright © 2010 Pearson Education, Inc. Figure 7.18
Dura andarachnoid
mater
Caudaequina
Cervicalspinal nerves
Lumbarspinal nerves
Sacralspinal nerves
Thoracicspinal nerves
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Gray Matter
• Dorsal horns—interneurons that receive sensory input
• Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots
• Dorsal root (spinal) ganglia—contain cell bodies of sensory neurons
Copyright © 2010 Pearson Education, Inc. Figure 12.32
Somaticsensoryneuron
Dorsal root (sensory)
Dorsal root ganglion
Visceralsensory neuron
Somaticmotor neuron
Spinal nerve
Ventral root(motor)
Ventral horn(motor neurons)
Dorsal horn (interneurons)
Visceralmotorneuron
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Copyright © 2010 Pearson Education, Inc. Figure 7.19
(b) The spinal cord and its meningeal coverings
Central canal
Pia mater
Arachnoid mater
Spinal dura mater
Dorsal horn Graymatter
Lateral hornVentral hornWhite
matterDorsal rootganglion
Dorsal root
Ventral root
Spinal nerve
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White Matter
• Mainly ascending (sensory) and descending (motor) tracts
• Tracts are located in three white columns on each side—posterior, lateral, and anterior columns
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Spinal Cord Trauma
• Flaccid paralysis—severe damage to the ventral root or ventral horn cells
• Impulses do not reach muscles; there is no voluntary or involuntary control of muscles
• Muscles atrophy
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Structure of a Nerve
• Cordlike organ of the PNS
• Bundle of myelinated and unmyelinated peripheral axons enclosed by CT
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Structure of a Nerve
• Connective tissue coverings include:
• Endoneurium—loose CT; encloses axons and their myelin sheaths
• Perineurium—coarse CT ; bundles fibers into fascicles
• Epineurium—tough fibrous sheath around a nerve
Copyright © 2010 Pearson Education, Inc. Figure 7.20
Bloodvessels
Fascicle
Epineurium
Perineurium
Endoneurium
AxonMyelin sheath
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20
Classifying Nerves
• Mixed nerves carry both sensory and motor fibers
• Afferent (sensory) nerves carry impulses toward CNS
• Efferent (motor) nerves carry impulses away from CNS
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23
Spinal Nerves • A spinal nerve is formed where ventral and dorsal roots fuse
• After spinal nerve is formed it divides into dorsal and ventral rami
• Ventral Rami form intercostal nerves (T1-T12) and networks of nerves called plexuses
• Plexuses serve limbs:
• Brachial plexus
• Lumbar plexus
• Sacral plexus
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21
Cranial Nerves
• 12 pairs
• Extend from base of brain
• Primarily innervate head and neck (except Vagus N.)
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22
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• Sensory only
• CN I (Olfactory) -smell
• CN II (Optic) -vision
• CN VIII (Vestibulocochlear) -Hearing and balance
• Remaining cranial nerves are motor or mixed
11
Cranial Nerves
Copyright © 2010 Pearson Education, Inc.
Somatic & Autonomic Nervous System Compared
Somatic Nervous System Autonomic Nervous System
The axon of ONE motor neuron extends all the way to skeletal
muscle
A chain of TWO motor neurons
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• Somatic nervous system
• All somatic motor neurons release acetylcholine (ACh)
• ANS
• Preganglionic fibers release acetylcholine (Ach)
• Postganglionic fibers release norepinephrine or ACh at effectors
Somatic & Autonomic Nervous System Compared
Copyright © 2010 Pearson Education, Inc.
Skeletal muscle
Cell bodies in centralnervous system Peripheral nervous system Effect
Effectororgans
ACh
AChSmooth muscle(e.g., in gut),glands, cardiacmuscle
Ganglion
Adrenal medulla Blood vessel
ACh
ACh
ACh
NE
Epinephrine andnorepinephrine
Acetylcholine (ACh) Norepinephrine (NE)
Ganglion
Neuro-transmitterat effector
Single neuron from CNS to effector organs
Two-neuron chain from CNS to effector organs
SO
MA
TIC
NER
VO
US
SYSTE
M
AU
TO
NO
MIC
NER
VO
US
SYS
TEM
PA
RA
SYM
PA
TH
ETIC
SYM
PA
TH
ETIC
Figure 7.24
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Divisions of the ANS
1.Sympathetic division
2.Parasympathetic division
• Dual innervation
• Most visceral organs are served by both divisions, but they cause opposite effects
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Role of the Sympathetic Division
• Mobilizes the body during activity; “fight-or-flight” system
• Promotes adjustments during exercise, or when threatened
• Blood flow directed to skeletal muscles & heart
• Bronchioles dilate
• Liver releases glucose
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Role of the Parasympathetic Division
• Promotes maintenance activities, conserves body energy
• Its activity is illustrated in a person who relaxes, reading, after a meal
• Blood pressure, heart rate, and respiratory rates are low
• GI tract activity is high
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Salivaryglands
Eye
Skin*
Heart
Lungs
Liverand gall-bladder
Genitals
Pancreas
Eye
Lungs
Bladder
Liver andgall-bladder
Pancreas
Stomach
Cervical
Sympatheticganglia
Cranial
Lumbar
Thoracic
Genitals
Heart
Salivaryglands
Stomach
Bladder
Adrenalgland
Parasympathetic Sympathetic
Sacral
Brainstem
L1
T1
Figure 7.25
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Sympathetic Division
• Preganglionic fibers pass through white rami communicantes and enter sympathetic trunk
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Spinal cord
Dorsal root
Ventral root
Sympathetictrunk ganglion
SympathetictrunkVentral ramusof spinal nerve
Gray ramuscommunicansWhite ramuscommunicans
(a) Location of the sympathetic trunk
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Sympathetic Trunks and Pathways
• Upon entering a sympathetic trunk ganglion a preganglionic fiber may do one of the following:
1.Synapse with a ganglionic neuron at the same level
2.Ascend or descend the sympathetic trunk to synapse at another level
3.Pass through trunk ganglion and emerge without synapsing
Copyright © 2010 Pearson Education, Inc. Figure 7.26
To effector
Blood vessels
Skin (arrectorpili musclesand sweatglands)
Dorsal root ganglionDorsal ramus ofspinal nerve
Dorsal root
Sympathetictrunk ganglion
Lateral horn (visceralmotor zone)
Ventral root
Sympathetic trunk
Gray ramuscommunicansWhite ramuscommunicans
Ventral ramus ofspinal nerve
Synapse at the same level
(b) Three pathways of sympathetic innervation
1
Copyright © 2010 Pearson Education, Inc. Figure 7.26
To effector
Blood vessels
Skin (arrectorpili musclesand sweatglands)
Synapse at a higher or lower level
(b) Three pathways of sympathetic innervation
2
Copyright © 2010 Pearson Education, Inc. Figure 7.26
Splanchnic nerve
Collateral ganglion
Target organin abdomen
Synapse in a distant collateral ganglionanterior to the vertebral column
(b) Three pathways of sympathetic innervation
3
Copyright © 2010 Pearson Education, Inc. Figure 7.19
(b) The spinal cord and its meningeal coverings
Central canal
Pia mater
Arachnoid mater
Spinal dura mater
Dorsal horn Graymatter
Lateral hornVentral hornWhite
matterDorsal rootganglion
Dorsal root(fans out into dorsal rootlets)
Ventral root(derived from severalventral rootlets)
Spinal nerve
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