Transcript 12 - Dr. Jerry Cronin
© Annie Leibovitz/Contact Press Images PowerPoint ® Lecture Slides prepared by
Human Anatomy & Physiology
Atlantic Cape Community Ninth Edition College
C H A P T E R
12
The Central Nervous System: Part D
© 2013 Pearson Education, Inc.
Spinal Cord: Gross Anatomy and Protection
• Location – Begins at the foramen magnum – Ends at L 1 • Functions or L 2 vertebra – Provides two-way communication to and from brain – Contains spinal reflex centers © 2013 Pearson Education, Inc.
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 L – Site of lumbar puncture or tap 1 or L 2 © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
Figure 12.27 Diagram of a lumbar tap.
T 12 L 5 L 4
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Inter vertebral disc L 5 Arachnoid mater S 1 Ligamentum flavum Lumbar puncture needle entering subarachnoid space Supra spinous ligament Filum terminale 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 Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves
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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.
Terminus of medulla oblongata of brain Spinal nerve rootlets Dorsal median sulcus of spinal cord
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Cervical spinal cord.
Cranial dura mater Sectioned pedicles of cervical vertebrae
Figure 12.26c Gross structure of the spinal cord, dorsal view.
Spinal cord Denticulate ligament Arachnoid mater
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Thoracic spinal cord, showing denticulate ligaments.
Vertebral arch Denticulate ligament Dorsal median sulcus Dorsal root Spinal dura mater
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 Inferior end of spinal cord, showing conus medullaris, cauda equina, and filum terminale.
Filum terminale
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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 © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
Figure 12.28a Anatomy of the spinal cord.
Epidural space (contains fat) Subdural space Subarachnoid space (contains CSF) Cross section of spinal cord and vertebra Pia mater Arachnoid mater Dura mater Spinal meninges Bone of vertebra Dorsal root ganglion Body of vertebra
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Figure 12.28b Anatomy of the spinal cord.
White columns Dorsal funiculus Ventral funiculus Lateral funiculus Dorsal root ganglion Spinal nerve Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) The spinal cord and its meningeal coverings
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Dorsal median sulcus Gray commissure Dorsal horn Ventral horn Lateral horn Gray matter Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater
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 © 2013 Pearson Education, Inc.
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) © 2013 Pearson Education, Inc.
Figure 12.29 Organization of the gray matter of the spinal cord.
Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Somatic motor neuron Dorsal root (sensory) Dorsal root ganglion Spinal nerve Dorsal horn (interneurons) SS VS VM SM Ventral root (motor) Ventral horn (motor neurons) 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
© 2013 Pearson Education, Inc.
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) © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
Neuronal Pathway Generalizations
• • • • • Major spinal tracts part of multineuron pathways
Decussation
side – Pathways cross to other
Relay
– Consist of two or three neurons
Somatotopy
– precise spatial relationship
Symmetry
– pathways paired symmetrically © 2013 Pearson Education, Inc.
Figure 12.30 Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional view.
Ascending tracts Dorsal white column Fasciculus gracilis Fasciculus cuneatus Dorsal spinocerebellar tract Ventral spinocerebellar tract Lateral spinothalamic tract Ventral spinothalamic tract Ventral white commissure Descending tracts Lateral reticulospinal tract Lateral corticospinal tract Rubrospinal tract Medial reticulospinal tract Ventral corticospinal tract Vestibulospinal tract Tectospinal tract
© 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
Ascending Pathways
•
Second-order neuron
– Interneuron – Cell body in dorsal horn of spinal cord or medullary nuclei – Axons extend to thalamus or cerebellum © 2013 Pearson Education, Inc.
Ascending Pathways
•
Third-order neuron
– Interneuron – Cell body in thalamus – Axon extends to somatosensory cortex – No third-order neurons in cerebellum © 2013 Pearson Education, Inc.
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
cerebellum terminate in the © 2013 Pearson Education, Inc.
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) © 2013 Pearson Education, Inc.
Figure 12.31a Pathways of selected ascending spinal cord tracts. (2 of 2) spinocerebellar (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 © 2013 Pearson Education, Inc.
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 Lumbar spinal cord
Axons of first-order neurons Temperature receptors Spinothalamic pathway
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Figure 12.31b Pathways of selected ascending spinal cord tracts. (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus
Cerebrum Midbrain
© 2013 Pearson Education, Inc.
Cerebellum Pons
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) spinocerebellar (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 © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
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
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Pyramidal (lateral and ventral corticospinal) pathways
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
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Somatic motor neurons (lower motor neurons) Pyramidal (lateral and ventral corticospinal) pathways
Indirect (Multineuronal) System
• Complex and multisynaptic • Includes brain stem motor nuclei, and all motor pathways except pyramidal pathways © 2013 Pearson Education, Inc.
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 Midbrain
© 2013 Pearson Education, Inc.
Cerebellum Pons
Red nucleus 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
© 2013 Pearson Education, Inc.
Rubrospinal tract
Spinal Cord Trauma
• Functional losses – Paresthesias • Sensory loss –
Paralysis
• Loss of motor function © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
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 T 1 and L 1
Quadriplegia
—transection in cervical region
Spinal shock
– transient period of functional loss caudal to lesion © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
Assessing CNS Dysfunction
• Reflex tests • Imaging techniques – CT, MRI, PET, radiotracer dyes for Alzheimer's, ultrasound, cerebral angiography © 2013 Pearson Education, Inc.
Developmental Aspects of the CNS
•
Ectoderm
thickens, forming neural plate – Invaginates, forming
neural groove
by
neural folds
flanked –
Neural crest
cells forms from migrating neural fold – Neural groove deepens week • Differentiates to CNS
neural tube
by 4 th © 2013 Pearson Education, Inc.
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 White matter Alar plate: interneurons Basal plate: motor neurons
© 2013 Pearson Education, Inc.
Neural tube cells 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 © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
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 © 2013 Pearson Education, Inc.
Figure 12.33 Development of the neural tube from embryonic ectoderm.
Head 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.
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
© 2013 Pearson Education, Inc.
Neural tube Tail 3 The neural groove becomes the neural tube, which will form CNS structures.
Slide 1
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.
Head Slide 4 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 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
© 2013 Pearson Education, Inc.
Neural tube Tail 3 The neural groove becomes the neural tube, which will form CNS structures.
Slide 5