1. The nervous system: Part C

2. Somatic nervous system
Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
Motor (efferent) division
Somatic nervous system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division

3. Spinal Cord Location Functions Begins at the foramen magnum
Ends at L1 vertebra
Functions
Provides two-way communication to and from the brain
Contains spinal reflex centers

4. Spinal Cord Spinal nerves Cauda equina 31 pairs
The collection of nerve roots at the inferior end of the vertebral canal

5. Spinal Cord Protection
Bone
Meninges
CSF

6. Dura and arachnoid mater
Cervical
spinal nerves
Dura and
arachnoid
mater
Thoracic
spinal nerves
Lumbar
spinal nerves
Cauda
equina
Sacral
spinal nerves
Figure 7.18

7. 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

8. Dorsal horn (interneurons)
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
Visceral
sensory
neuron
Visceral
motor
neuron
Spinal nerve
Ventral horn
(motor neurons)
Ventral root
(motor)
Somatic
motor neuron
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Figure 12.32

9. (b) The spinal cord and its meningeal coverings
Dorsal horn
Gray
matter
White
matter
Ventral horn
Lateral horn
Dorsal root
ganglion
Spinal nerve
Central canal
Dorsal root
Ventral root
Pia mater
Arachnoid mater
Spinal dura mater
(b) The spinal cord and its meningeal coverings
Figure 7.19

10. White Matter
Mainly ascending (sensory) and descending (motor) tracts
Tracts are located in three white columns on each side—posterior, lateral, and anterior columns

11. 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

12. Structure of a Nerve
Cordlike organ of the PNS
Bundle of myelinated and unmyelinated peripheral axons enclosed by CT

13. Connective tissue coverings include:
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

14. Axon Myelin sheath Endoneurium Perineurium Epineurium Fascicle Blood
vessels
Figure 7.20

15. Classifying Nerves Mixed nerves carry both sensory and motor fibers
4/23/2017
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

16. 4/23/2017
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

17. Extend from base of brain
4/23/2017
Cranial Nerves
12 pairs
Extend from base of brain
Primarily innervate head and neck (except Vagus N.) 21

18. 4/23/2017 22

19. Remaining cranial nerves are motor or mixed
4/23/2017
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

20. Somatic & Autonomic Nervous System Compared
4/23/2017
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

21. 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

22. Figure 7.24 Neuro- transmitter at effector Cell bodies in central
nervous system
Effector
organs
Peripheral nervous system
Effect
Single neuron from CNS to effector organs
SOMATIC
NERVOUS
SYSTEM
ACh
Skeletal muscle
Two-neuron chain from CNS to effector organs
ACh NE
SYMPATHETIC
Ganglion
Epinephrine and
norepinephrine
ACh
AUTONOMIC NERVOUS SYSTEM
Adrenal medulla
Blood vessel
ACh
ACh
Smooth muscle
(e.g., in gut),
glands, cardiac
muscle
PARASYMPATHETIC
Ganglion
Acetylcholine (ACh)
Norepinephrine (NE)
Figure 7.24

23. Parasympathetic division Dual innervation
Divisions of the ANS
Sympathetic division
Parasympathetic division
Dual innervation
Most visceral organs are served by both divisions, but they cause opposite effects

24. 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

25. 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

26. Parasympathetic Sympathetic Eye Eye Brain stem Salivary glands Skin*
Cranial
Salivary
glands
Sympathetic
ganglia
Heart
Cervical
Lungs
Lungs T1
Heart
Stomach
Thoracic
Stomach
Pancreas
Liver
and gall-
bladder
Pancreas L1
Liver and
gall-
bladder
Adrenal
gland
Lumbar
Bladder
Bladder
Genitals
Genitals
Sacral
Figure 7.25

27. Sympathetic Division
Preganglionic fibers pass through white rami communicantes and enter sympathetic trunk

28. 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

29. Sympathetic Trunks and Pathways
Upon entering a sympathetic trunk ganglion a preganglionic fiber may do one of the following:
Synapse with a ganglionic neuron at the same level
Ascend or descend the sympathetic trunk to synapse at another level
Pass through trunk ganglion and emerge without synapsing

30. Lateral horn (visceral motor zone)
Dorsal root
Dorsal root ganglion
Dorsal ramus of
spinal nerve
Ventral ramus of
spinal nerve
Skin (arrector
pili muscles
and sweat
glands)
Gray ramus
communicans
Ventral root
White ramus
communicans
Sympathetic
trunk ganglion
Sympathetic trunk
To effector 1
Synapse at the same level
Blood vessels
(b) Three pathways of sympathetic innervation
Figure 7.26

31. Synapse at a higher or lower level
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
Figure 7.26

32. Synapse in a distant collateral ganglion
Splanchnic nerve
Collateral ganglion
Target organ
in abdomen
Synapse in a distant collateral ganglion
anterior to the vertebral column 3
(b) Three pathways of sympathetic innervation
Figure 7.26

33. (b) The spinal cord and its meningeal coverings
Dorsal horn
Gray
matter
White
matter
Ventral horn
Lateral horn
Dorsal root
ganglion
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
Figure 7.19