1. 12
The Central Nervous System: Part D

2. Spinal Cord: Gross Anatomy and Protection
Location
Begins at the foramen magnum
Ends at L1 or L2 vertebra
Functions
Provides two-way communication to and from brain
Contains spinal reflex centers
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3. Spinal Cord: Gross Anatomy and Protection
Bone, meninges, and CSF
Epidural space
Cushion of fat and network of veins in space between vertebrae and spinal dura mater
CSF in subarachnoid space
Dural and arachnoid membranes extend to sacrum, beyond end of cord at L1 or L2
Site of lumbar puncture or tap
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4. T12 L5 Ligamentum flavum Lumbar puncture needle entering subarachnoid
Figure Diagram of a lumbar tap.
T12 L5
Ligamentum
flavum
Lumbar puncture
needle entering
subarachnoid
space L4
Supra-
spinous
ligament L5
Filum
terminale S1
Inter-
vertebral
disc
Cauda equina
in subarachnoid
space
Arachnoid
mater
Dura
mater
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5. The spinal cord and its nerve roots, with the bony
Figure 12.26a Gross structure of the spinal cord, dorsal view.
Cervical
spinal
nerves
Cervical
enlargement
Dura and
arachnoid
mater
Thoracic
spinal nerves
Lumbar
enlargement
Conus
medullaris
Cauda
equina
Lumbar
spinal nerves
Filum
terminale
Sacral
spinal nerves
The spinal cord and its nerve roots, with the bony
vertebral arches removed. The dura mater and
arachnoid mater are cut open and reflected laterally.
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6. Cranial dura mater Terminus of medulla oblongata of brain Sectioned
Figure 12.26b Gross structure of the spinal cord, dorsal view.
Cranial
dura mater
Terminus of
medulla
oblongata
of brain
Sectioned
pedicles of
cervical
vertebrae
Spinal nerve
rootlets
Dorsal
median sulcus
of spinal cord
Cervical spinal cord.
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7. Thoracic spinal cord, showing denticulate ligaments.
Figure 12.26c Gross structure of the spinal cord, dorsal view.
Spinal cord
Vertebral
arch
Denticulate
ligament
Denticulate
ligament
Dorsal
median
sulcus
Arachnoid
mater
Dorsal root
Spinal dura
mater
Thoracic spinal cord, showing
denticulate ligaments.
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8. Spinal nerves (Part of PNS) Cervical and lumbosacral enlargements
Spinal Cord
Spinal nerves (Part of PNS)
31 pairs
Cervical and lumbosacral enlargements
Nerves serving upper and lower limbs emerge here
Cauda equina
Collection of nerve roots at inferior end of vertebral canal
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9. Cross-sectional Anatomy
Two lengthwise grooves partially divide cord into right and left halves
Ventral (anterior) median fissure
Dorsal (posterior) median sulcus
Gray commissure—connects masses of gray matter; encloses central canal
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10. Cross section of spinal cord and vertebra
Figure 12.28a Anatomy of the spinal cord.
Epidural space
(contains fat)
Pia mater
Arachnoid mater
Spinal meninges
Subdural space
Dura mater
Subarachnoid
space
(contains CSF)
Bone of
vertebra
Dorsal root
ganglion
Body
of vertebra
Cross section of spinal cord and vertebra
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11. Figure 12.28b Anatomy of the spinal cord.
Dorsal median sulcus
Dorsal funiculus
Gray commissure
Dorsal horn
White
columns
Ventral funiculus
Gray
matter
Ventral horn
Lateral funiculus
Lateral horn
Dorsal root
ganglion
Spinal nerve
Central canal
Dorsal root
(fans out into
dorsal rootlets)
Ventral median fissure
Pia mater
Ventral root
(derived from several
ventral rootlets)
Arachnoid mater
Spinal dura mater
The spinal cord and its meningeal coverings
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12. Gray Matter
Dorsal horns - interneurons that receive somatic and visceral sensory input
Ventral horns - some interneurons; somatic motor neurons; axons exit cord via ventral roots
Lateral horns (only in thoracic and superior lumbar regions) - sympathetic neurons
Dorsal roots – sensory input to cord
Dorsal root (spinal) ganglia—cell bodies of sensory neurons
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13. Run in three directions
White Matter
Myelinated and nonmyelinated nerve fibers allow communication between parts of spinal cord, and spinal cord and brain
Run in three directions
Ascending – up to higher centers (sensory inputs)
Descending – from brain to cord or lower cord levels (motor outputs)
Transverse – from one side to other (commissural fibers)
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14. spinocerebellar tract Lateral corticospinal tract
Figure Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional view.
Ascending tracts
Descending tracts
Ventral white
commissure
Dorsal
white
column
Fasciculus gracilis
Fasciculus cuneatus
Lateral
reticulospinal tract
Dorsal
spinocerebellar tract
Lateral
corticospinal
tract
Ventral
spinocerebellar
tract
Rubrospinal tract
Medial
reticulospinal tract
Lateral spinothalamic
tract
Ventral
corticospinal tract
Ventral spinothalamic
tract
Vestibulospinal tract
Tectospinal tract
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15. Ascending Pathways Three main pathways:
Two transmit somatosensory information to sensory cortex via thalamus
Dorsal column–medial lemniscal pathways
Spinothalamic pathways
Provide discriminatory touch and conscious proprioception
Spinocerebellar tracts terminate in the cerebellum
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16. Medial lemniscus (tract) (axons of second-order neurons)
Figure 12.31a Pathways of selected ascending spinal cord tracts. (2 of 2)
Dorsal
spinocerebellar
tract (axons of
second-order
neurons)
Medial lemniscus (tract)
(axons of second-order neurons)
Nucleus gracilis
Nucleus cuneatus
Medulla oblongata
Fasciculus cuneatus
(axon of first-order sensory neuron)
Joint stretch
receptor
(proprioceptor)
Axon of
first-order
neuron
Cervical spinal cord
Fasciculus gracilis
(axon of first-order sensory neuron)
Muscle
spindle
(proprioceptor)
Lumbar spinal cord
Touch
receptor
Spinocerebellar pathway
Dorsal column–medial lemniscal
pathway
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17. Spinocerebellar pathway Dorsal column–medial lemniscal pathway
Figure 12.31a Pathways of selected ascending spinal cord tracts. (1 of 2)
Primary
somatosensory
cortex
Axons of third-order
neurons
Thalamus
Cerebrum
Midbrain
Cerebellum
Pons
Spinocerebellar pathway
Dorsal column–medial lemniscal
pathway
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18. Spinothalamic Pathways
Lateral and ventral spinothalamic tracts
Transmit pain, temperature, coarse touch, and pressure impulses within lateral spinothalamic tract
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19. Spinocerebellar Tracts
Ventral and dorsal tracts
Convey information about muscle or tendon stretch to cerebellum
Used to coordinate muscle activity
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20. Indirect (Multineuronal) System
Reticulospinal and vestibulospinal tracts—maintain balance
Rubrospinal tracts—control flexor muscles
Superior colliculi and tectospinal tracts mediate head movements in response to visual stimuli
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21. Spinal Cord Trauma Functional losses Paresthesias Paralysis
Sensory loss
Paralysis
Loss of motor function
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22. Flaccid paralysis—severe damage to ventral root or ventral horn cells
Spinal Cord Trauma
Flaccid paralysis—severe damage to 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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23. Spinal Cord Trauma
Spastic paralysis—damage to upper motor neurons of primary motor cortex
Spinal neurons remain intact; muscles are stimulated by reflex activity
No voluntary control of muscles
Muscles often shorten permanently
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24. Spinal shock – transient period of functional loss caudal to lesion
Spinal Cord Trauma
Transection
Cross sectioning of spinal cord at any level
Results in total motor and sensory loss in regions inferior to cut
Paraplegia—transection between T1 and L1
Quadriplegia—transection in cervical region
Spinal shock – transient period of functional loss caudal to lesion
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25. Destruction of ventral horn motor neurons by poliovirus
Poliomyelitis
Destruction of ventral horn motor neurons by poliovirus
Muscles atrophy
Death may occur from paralysis of respiratory muscles or cardiac arrest
Survivors often develop postpolio syndrome many years later from neuron loss
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26. Amyotrophic Lateral Sclerosis (ALS) (Lou Gehrig's Disease)
Destruction of ventral horn motor neurons and fibers of pyramidal tract
Symptoms—loss of ability to speak, swallow, and breathe
Death typically occurs within five years
Caused by environmental factors and genetic mutations involving RNA processing
Involves glutamate excitotoxicity
Drug riluzole interferes with glutamate signaling – only treatment
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27. Assessing CNS Dysfunction
Reflex tests
Imaging techniques
CT, MRI, PET, radiotracer dyes for Alzheimer's, ultrasound, cerebral angiography
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28. Developmental Aspects of the CNS
Ectoderm thickens, forming neural plate
Invaginates, forming neural groove flanked by neural folds
Neural crest forms from migrating neural fold cells
Neural groove deepens  neural tube by 4th week
Differentiates to CNS
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29. Developmental Aspects of the CNS
Gender-specific areas appear in both brain and spinal cord, depending on presence or absence of fetal testosterone
Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or infection can harm developing CNS
Smoking decreases oxygen in blood, which can lead to neuron death and fetal brain damage
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30. Developmental Aspects of the CNS
Hypothalamus one of last areas of CNS to develop
Premature infants poor body temperature regulation
Visual cortex develops slowly over first 11 weeks
Neuromuscular coordination progresses in superior-to-inferior and proximal-to-distal directions along with myelination
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31. Developmental Aspects of the CNS
Age brings some cognitive declines, but not significant in healthy individuals until 80s
Shrinkage of brain accelerates in old age
Excessive alcohol use and boxing cause signs of senility unrelated to aging process
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