Transcript 12 - Dr. Jerry Cronin

PowerPoint® Lecture Slides
prepared by
Barbara Heard,
Atlantic Cape Community
Ninth Edition
College
Human Anatomy & Physiology
CHAPTER
12
The Central
Nervous
System:
Part D
© Annie Leibovitz/Contact Press Images
© 2013 Pearson Education, Inc.
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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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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Spinal Cord: Gross Anatomy and Protection
• Terminates in conus medullaris
• Filum terminale extends to coccyx
– Fibrous extension of conus covered with pia
mater
– Anchors spinal cord
• Denticulate ligaments
– Extensions of pia mater that secure cord to
dura mater
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Figure 12.27 Diagram of a lumbar tap.
T12
L5
Ligamentum
flavum
Lumbar puncture
needle entering
subarachnoid
space
L4
Supraspinous
ligament
Filum
terminale
L5
S1
Intervertebral
disc
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Arachnoid
mater
Dura
mater
Cauda equina
in subarachnoid
space
Figure 12.26a Gross structure of the spinal cord, dorsal view.
Cervical
enlargement
Dura and
arachnoid
mater
Lumbar
enlargement
Conus
medullaris
Cauda
equina
Filum
terminale
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Cervical
spinal
nerves
Thoracic
spinal nerves
Lumbar
spinal nerves
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.
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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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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Figure 12.26d Gross structure of the spinal cord, dorsal view.
Spinal cord
Cauda
equina
First lumbar
vertebral arch
(cut across)
Conus
medullaris
Spinous
process of
second lumbar
vertebra
Filum
terminale
Inferior end of spinal cord, showing
conus medullaris, cauda equina, and
filum terminale.
© 2013 Pearson Education, Inc.
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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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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Figure 12.28a Anatomy of the spinal cord.
Epidural space
(contains fat)
Subdural space
Subarachnoid
space
(contains CSF)
Pia mater
Arachnoid mater
Dura mater
Spinal meninges
Bone of
vertebra
Dorsal root
ganglion
Body
of vertebra
Cross section of spinal cord and vertebra
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Figure 12.28b Anatomy of the spinal cord.
Dorsal funiculus
White
columns
Ventral funiculus
Lateral funiculus
Dorsal median sulcus
Gray commissure
Dorsal horn
Gray
Ventral horn
matter
Lateral horn
Dorsal root
ganglion
Spinal nerve
Dorsal root
(fans out into
dorsal rootlets)
Central canal
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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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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Zones of Spinal Gray Matter
• Per relative involvement in innervating
somatic and visceral regions of body
• Somatic sensory (SS)
• Visceral sensory (VS)
• Visceral (autonomic) motor (VM)
• Somatic motor (SM)
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Figure 12.29 Organization of the gray matter of the spinal cord.
Dorsal root
(sensory)
Dorsal horn (interneurons)
Dorsal root
ganglion
SS
VS
Somatic sensory neuron
VM
Visceral sensory
neuron
SM
Visceral motor
neuron
Somatic motor neuron
Spinal nerve
Ventral horn
(motor neurons)
Ventral root
(motor)
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SS
Interneurons receiving input from somatic sensory neurons
VS
Interneurons receiving input from visceral sensory neurons
VM
Visceral motor (autonomic) neurons
SM
Somatic motor neurons
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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White Matter
• Divided into three white columns
(funiculi) on each side
– Dorsal (posterior), lateral, and ventral
(anterior)
• Each spinal tract composed of axons with
similar destinations and functions
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Neuronal Pathway Generalizations
• Major spinal tracts part of multineuron
pathways
• Decussation – Pathways cross to other
side
• Relay – Consist of two or three neurons
• Somatotopy – precise spatial relationship
• Symmetry – pathways paired
symmetrically
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Figure 12.30 Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional view.
Ascending tracts
Dorsal Fasciculus gracilis
white Fasciculus cuneatus
column
Dorsal
spinocerebellar tract
Ventral
spinocerebellar
tract
Lateral spinothalamic
tract
Ventral spinothalamic
tract
Descending tracts
Ventral white
commissure
Lateral
reticulospinal tract
Lateral
corticospinal
tract
Rubrospinal tract
Medial
reticulospinal tract
Ventral
corticospinal tract
Vestibulospinal tract
Tectospinal tract
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Ascending Pathways
• Consist of three neurons
• First-order neuron
– Conducts impulses from cutaneous receptors
and proprioceptors
– Branches diffusely as enters spinal cord or
medulla
– Synapses with second-order neuron
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Ascending Pathways
• Second-order neuron
– Interneuron
– Cell body in dorsal horn of spinal cord or
medullary nuclei
– Axons extend to thalamus or cerebellum
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Ascending Pathways
• Third-order neuron
– Interneuron
– Cell body in thalamus
– Axon extends to somatosensory cortex
– No third-order neurons in cerebellum
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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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Dorsal Column–Medial Lemniscal Pathways
• Transmit input to somatosensory cortex for
discriminative touch and vibrations
• Composed of paired fasciculus cuneatus
and fasciculus gracilis in spinal cord and
medial lemniscus in brain (medulla to
thalamus)
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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)
Axon of
first-order
neuron
Muscle
spindle
(proprioceptor)
Joint stretch
receptor
(proprioceptor)
Cervical spinal cord
Fasciculus gracilis
(axon of first-order sensory neuron)
Lumbar spinal cord
Touch
receptor
Spinocerebellar pathway Dorsal column–medial lemniscal
pathway
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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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Spinothalamic Pathways
• Lateral and ventral spinothalamic tracts
• Transmit pain, temperature, coarse touch,
and pressure impulses within lateral
spinothalamic tract
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Figure 12.31b Pathways of selected ascending spinal cord tracts. (2 of 2)
Lateral
spinothalamic
tract (axons of
second-order
neurons)
Medulla oblongata
Pain receptors
Cervical spinal cord
Axons of first-order
neurons
Temperature
receptors
Lumbar spinal cord
Spinothalamic pathway
© 2013 Pearson Education, Inc.
Figure 12.31b Pathways of selected ascending spinal cord tracts. (1 of 2)
Primary
somatosensory
cortex
Axons of third-order
neurons
Thalamus
Cerebrum
Midbrain
Cerebellum
Pons
© 2013 Pearson Education, Inc.
Spinothalamic pathway
Spinocerebellar Tracts
• Ventral and dorsal tracts
• Convey information about muscle or
tendon stretch to cerebellum
– Used to coordinate muscle activity
© 2013 Pearson Education, Inc.
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)
Axon of
first-order
neuron
Muscle
spindle
(proprioceptor)
Joint stretch
receptor
(proprioceptor)
Cervical spinal cord
Fasciculus gracilis
(axon of first-order sensory neuron)
Lumbar spinal cord
Touch
receptor
Spinocerebellar pathway Dorsal column–medial lemniscal
pathway
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Descending Pathways and Tracts
• Deliver efferent impulses from brain to
spinal cord
• Two groups
– Direct pathways—pyramidal tracts
– Indirect pathways—all others
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Descending Pathways and Tracts
• Motor pathways involve two neurons:
– Upper motor neurons
• Pyramidal cells in primary motor cortex
– Lower motor neurons
• Ventral horn motor neurons
• Innervate skeletal muscles
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The Direct (Pyramidal) Pathways
• Impulses from pyramidal neurons in
precentral gyri pass through pyramidal
(corticospinal)l tracts
• Descend without synapsing
• Axons synapse with interneurons or
ventral horn motor neurons
• Direct pathway regulates fast and fine
(skilled) movements
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Figure 12.32a Three descending pathways by which the brain influences movement. (1 of 2)
Pyramidal cells
(upper motor neurons)
Primary motor cortex
Internal capsule
Cerebrum
Midbrain
Cerebral
peduncle
Cerebellum
Pons
Pyramidal (lateral and ventral corticospinal) pathways
© 2013 Pearson Education, Inc.
Figure 12.32a Three descending pathways by which the brain influences movement. (2 of 2)
Ventral
corticospinal
tract
Medulla oblongata
Pyramids
Decussation
of pyramids
Lateral
corticospinal
tract
Cervical spinal cord
Skeletal
muscle
Lumbar spinal cord
Somatic motor neurons
(lower motor neurons)
Pyramidal (lateral and ventral corticospinal) pathways
© 2013 Pearson Education, Inc.
Indirect (Multineuronal) System
• Complex and multisynaptic
• Includes brain stem motor nuclei, and all
motor pathways except pyramidal
pathways
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Indirect (Multineuronal) System
• These pathways regulate
– Axial muscles maintaining balance and
posture
– Muscles controlling coarse limb movements
– Head, neck, and eye movements that follow
objects in visual field
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Figure 12.32b Three descending pathways by which the brain influences movement. (1 of 2)
Cerebrum
Red nucleus
Midbrain
Cerebellum
Pons
© 2013 Pearson Education, Inc.
Rubrospinal tract
Figure 12.32b Three descending pathways by which the brain influences movement. (2 of 2)
Rubrospinal tract
Medulla oblongata
Cervical spinal cord
Lumbar spinal cord
Rubrospinal tract
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Spinal Cord Trauma
• Functional losses
– Paresthesias
• Sensory loss
– Paralysis
• Loss of motor function
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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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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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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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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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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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Assessing CNS Dysfunction
• Reflex tests
• Imaging techniques
– CT, MRI, PET, radiotracer dyes for Alzheimer's,
ultrasound, cerebral angiography
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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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Developmental Aspects of the CNS
• Both sides of spinal cord bear a dorsal
alar plate and a ventral basal plate
– Alar plate  interneurons
– Basal plate  motor neurons
• Neural crest cells form dorsal root ganglia
© 2013 Pearson Education, Inc.
Figure 12.34 Structure of the embryonic spinal cord.
Dorsal root ganglion: sensory
neurons from neural crest
Alar plate:
interneurons
White
matter
Basal plate:
motor neurons
Neural tube
cells
© 2013 Pearson Education, Inc.
Central
cavity
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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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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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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Figure 12.33 Development of the neural tube from embryonic ectoderm.
Head
Neural fold
forming
Slide 1
Surface
ectoderm
Neural plate
Tail
1 The neural plate forms from surface ectoderm. It then
invaginates, forming the neural groove flanked by neural folds.
Neural crest
Neural
groove
2 Neural fold cells migrate to form the neural crest, which
will form much of the PNS and many other structures.
Head
Surface
ectoderm
Neural
tube
Tail
© 2013 Pearson Education, Inc.
3 The neural groove becomes the neural tube, which will
form CNS structures.
Figure 12.33 Development of the neural tube from embryonic ectoderm.
Head
Slide 2
Neural fold
forming
Surface
ectoderm
Neural plate
Tail
1 The neural plate forms from surface ectoderm. It then
invaginates, forming the neural groove flanked by neural folds.
© 2013 Pearson Education, Inc.
Figure 12.33 Development of the neural tube from embryonic ectoderm.
Slide 3
Neural crest
Neural
Groove
2 Neural fold cells migrate to form the neural crest, which
will form much of the PNS and many other structures.
© 2013 Pearson Education, Inc.
Figure 12.33 Development of the neural tube from embryonic ectoderm.
Slide 4
Head
Surface
ectoderm
Neural
tube
Tail
3 The neural groove becomes the neural tube, which will
form CNS structures.
© 2013 Pearson Education, Inc.
Figure 12.33 Development of the neural tube from embryonic ectoderm.
Head
Neural fold
forming
Slide 5
Surface
ectoderm
Neural plate
Tail
1 The neural plate forms from surface ectoderm. It then
invaginates, forming the neural groove flanked by neural folds.
Neural crest
Neural
groove
2 Neural fold cells migrate to form the neural crest, which
will form much of the PNS and many other structures.
Head
Surface
ectoderm
Neural
tube
Tail
© 2013 Pearson Education, Inc.
3 The neural groove becomes the neural tube, which will
form CNS structures.