Download Ch. 7c The Nervous System

THE NERVOUS SYSTEM: PART C
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Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
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Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
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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Spinal Cord Protection
• Bone
• Meninges
• CSF
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Cervical
spinal nerves
Dura and
arachnoid
mater
Cauda
equina
Thoracic
spinal nerves
Lumbar
spinal nerves
Sacral
spinal nerves
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Figure 7.18
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
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Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
Visceral
sensory
neuron
Visceral
motor
neuron
Somatic
motor neuron
Spinal nerve
Ventral root
(motor)
Ventral horn
(motor neurons)
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
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Figure 12.32
White
matter
Dorsal root
ganglion
Dorsal horn Gray
Ventral horn matter
Lateral horn
Spinal nerve
Central canal
Dorsal root
Ventral root
Pia mater
Arachnoid mater
Spinal dura mater
(b) The spinal cord and its meningeal coverings
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Figure 7.19
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
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Endoneurium
Axon
Myelin sheath
Perineurium
Epineurium
Fascicle
Blood
vessels
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Figure 7.20
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
20
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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
23
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Cranial Nerves
• 12 pairs
• Extend from base of brain
• Primarily innervate head and neck
(except Vagus N.)
21
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22
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Cranial Nerves
• Sensory only
• CN I (Olfactory) -smell
• CN II (Optic) -vision
• CN VIII (Vestibulocochlear) -Hearing and balance
• Remaining cranial nerves are motor or mixed
11
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Somatic & Autonomic Nervous System
Compared
Somatic Nervous System
The axon of ONE motor neuron
extends all the way to skeletal
muscle
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Autonomic Nervous System
A chain of TWO motor neurons
Somatic & Autonomic Nervous System
Compared
• Somatic nervous system
• All somatic motor neurons release acetylcholine (ACh)
• ANS
• Preganglionic fibers release acetylcholine (Ach)
• Postganglionic fibers release norepinephrine or ACh at
effectors
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Cell bodies in central
nervous system
Peripheral nervous system
Neurotransmitter
at effector
Effector
organs
Effect
SOMATIC
NERVOUS
SYSTEM
Single neuron from CNS to effector organs
ACh
Skeletal muscle
NE
SYMPATHETIC
ACh
Ganglion
Epinephrine and
norepinephrine
ACh
Adrenal medulla
PARASYMPATHETIC
AUTONOMIC NERVOUS SYSTEM
Two-neuron chain from CNS to effector organs
Acetylcholine (ACh)
ACh
Ganglion
Blood vessel
ACh
Smooth muscle
(e.g., in gut),
glands, cardiac
muscle
Norepinephrine (NE)
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Figure 7.24
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-orflight” 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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Parasympathetic
Sympathetic
Eye
Brain
stem
Salivary
glands
Heart
Eye
Skin*
Cranial
Sympathetic
ganglia
Salivary
glands
Cervical
Lungs
Lungs
T1
Heart
Stomach
Stomach
Thoracic
Pancreas
Liver
and gallbladder
Pancreas
L1
Liver and
gallbladder
Adrenal
gland
Lumbar
Bladder
Bladder
Genitals
Genitals
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Sacral
Figure 7.25
Sympathetic Division
• Preganglionic fibers pass through white rami
communicantes and enter sympathetic trunk
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Spinal cord
Dorsal root
Ventral root
Sympathetic
trunk ganglion
Sympathetic
trunk
Ventral ramus
of spinal nerve
Gray ramus
communicans
White ramus
communicans
(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
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Lateral horn (visceral
motor zone)
Skin (arrector
pili muscles
and sweat
glands)
Dorsal root
Dorsal root ganglion
Dorsal ramus of
spinal nerve
Ventral ramus of
spinal nerve
Gray ramus
communicans
White ramus
communicans
To effector
Ventral root
Sympathetic
trunk ganglion
Sympathetic trunk
1 Synapse at the same level
Blood vessels
(b) Three pathways of sympathetic innervation
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Figure 7.26
Skin (arrector
pili muscles
and sweat
glands)
To effector
Blood vessels
2 Synapse at a higher or lower level
(b) Three pathways of sympathetic innervation
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Figure 7.26
Splanchnic nerve
Collateral ganglion
Target organ
in abdomen
3 Synapse in a distant collateral ganglion
anterior to the vertebral column
(b) Three pathways of sympathetic innervation
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Figure 7.26
White
matter
Dorsal root
ganglion
Dorsal horn Gray
Ventral horn matter
Lateral horn
Spinal nerve
Central canal
Dorsal root
(fans out into
dorsal rootlets)
Ventral root
(derived from several
ventral rootlets)
Pia mater
Arachnoid mater
Spinal dura mater
(b) The spinal cord and its meningeal coverings
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Figure 7.19