Download Lecture VIII. Spinal Cord

Lecture VIII. The Spinal Cord,
Reflexes and Brain Pathways
Bio 3411
Monday
September 27, 2010
Readings
NEUROSCIENCE 4th ed:
Review Chapter 1 pp. 11-22;
Read Chapter 9 pp. 207-212, 218
Study Box 9A, Figure 9.8 & Refer to Table 9.1;
Read Chapter 16 pp. 399–414
Study figures 16.2,16.3,16.4, 16.14
Read Chapter 17 pp. 432–436
Study figure 17.9
THE BRAIN ATLAS 3rd ed:
Read pp. 4-17 on class web site
Look at pp 36, 43, 49, 75-76, 140, 151, 154, 170-171, 182-183, 200201.
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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What the last Lecture was about
• The Initiation of the Central Nervous System
• CNS Growth and Pattern Development
• Bug Brains
• Several Mechanisms for Directing the Show
(scripts conserved)
• How did vertebrate and invertebrate patterns
arise?
• Reprise and overview the discussions of
developmental sequences and mechanisms in the
nervous system
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Overview for this Lecture
Spinal Cord
Columns, Horns, Spinal Segments
Spinal Nerves
Dermatomes, Motor Units
Reflexes
“Knee Jerk”- Myotatic or Stretch Reflex
Withdrawal & Crossed Extensor Reflexes
Two Spinal Pathways
Sensory - Dorsal Column/ Medial lemniscus
Motor - Cortico-spinal Tract
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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(The Brain Atlas 3rd ed,
p. 8)
Cervical (C) - Neck
Thoracic (T) - Chest
Segments of
spinal cord,
spinal nerves
and vertebrae
Lumbar (L) - Back
Sacral (S) - Pelvis
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Human spinal
cord from side,
front and back
≈ 50 cm
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Internal Structure
• Canal = tube
• White Matter - columns, tracts
anterior up and down to and from brain
lateral down from brain (>>up)
posterior mainly up to brain
• Gray Matter - posterior (dorsal) horn “sensory”,
anterior (ventral) horn “motor”
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Anterior Column
(white matter)
Front
(anterior/ventral)
Anterior
Horn
(gray
matter)
Section
of
human
spinal
cord
(C8)
myelin
stain
Lateral
Column
(white
matter)
Posterior
Horn
(gray
matter)
Posterior Column
(white matter)
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Back
(posterior/dorsal)
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
8
Anterior
Anterior
Horn
Column
Front
(anterior/ventral)
Section
of human
spinal
cord (C8)
cell body
stain
Lateral
Column
Posterior
Horn
September 27, 2010
Posterior
Back
Column
(posterior/dorsal)
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Cervical Cord
Sacral Cord
(The Brain Atlas 3rd ed,
p.151)
(The Brain Atlas 3rd ed,
p.154)
The size of white matter tracts (posterior, lateral and anterior columns) increases as more
axons are added on the way TO the brain and decreases as axons end on the way FROM
the the brain.
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Spinal Nerves
• Intervertebral foramen
• Segmental spinal nerve
• Compound action potential
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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The Brain Atlas 3rd ed,
p. 49.
Spinal
canal
Intervertebral
foramen
Left - Vertebral bones.
Right - Human spinal cord in cross–section showing anterior (ventral) and posterior
(dorsal) spinal roots and spinal or posterior (dorsal) root ganglion (posterior to
right).
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Segmental nerve: (posterior (dorsal) root = sensory - touch;
anterior (ventral) root = motor -movement; spinal or posterior
(dorsal) root ganglion = sensory nerve cell bodies)
Periphery
(skin, muscle,
etc.)
Spinal cord
Mixed spinal nerve
front = anterior
back = posterior
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Joseph Erlanger
Herbert Spencer
Gasser
George H.
Bishop
1874 - 1965
1888 - 1965
1889 - 1973
(Prix Nobel 1944)
(Prix Nobel 1944)
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Periphery (skin,
muscle, etc.)
Spinal cord
Mixed spinal nerve
front = anterior
back = posterior
Stimulate
(Shock)
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Record
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Discriminative
Touch
Conduction
Velocity m/s
Fast pain &
Temperature (cold)
Slow pain &
Temperature (warm)
Compound action
potential
Erlanger, Gasser (Bishop)
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Axon diameters differ in motor
and sensory nerves
Cross section of human muscle
(motor) nerve – myelin stain
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Cross section of human sensory
nerve – myelin stain
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Segmental Nerves
Spinal or Posterior (dorsal) Root, Ganglion
Cells & Sensory Nerves
(axons in from posterior (dorsal) root ganglia)
Dermatomes
Anterior (ventral) Root & Motor Nerves
(axons out from motor neurons)
Motor Units
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Spinal or Posterior (dorsal) Root
Ganglion Cells
Pseudo-Unipolar Neurons
(neurons start as bipolar cells and become “unipolar” during
development)
Single sensory endings
light & crude touch, pain, temperature and muscle senses
Axons diverge to multiple spinal targets
motor neurons - c, interneurons - c, spinal cord - b, and brain -a
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Segmental nerve (posterior (dorsal) root = sensory - touch; ventral
root = motor -movement; spinal or posterior (dorsal) root ganglion =
sensory nerve cell bodies)
Mixed spinal nerve
front = ventral
back = dorsal
Periphery
(skin, muscle,
etc.)
September 27, 2010
Spinal cord
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Dermatome =
The region (slice) of skin innervated by a single spinal or
posterior (dorsal) root ganglion
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Motor Units, Motor Neuron
Pools & Somatotopy
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Spinal Motor Neurons
• Multipolar
• Output Diverges to several or many muscle cells: motor unit
• Input Converges from –
spinal or posterior (dorsal) root ganglion cells
spinal interneurons
long tracts from from brain
• Integrate
• Map
flexors, extensors, proximal, distal
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Section of human spinal cord
(C8) myelin stain – anterior
horn
September 27, 2010
Section of human spinal cord
(C8) cell body stain – anterior
horn
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Motor Unit - A motor
neuron and the muscle
fibers it innervates.
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Motor Neurons to
Distal (farther)
Extensor muscles
Motor Neurons to
Proximal (nearer)
Extensor muscles
Motor neuron
“Quads”
Proximal (nearer)
Extensor muscles
pools (nuclei) are
Motor Neurons to
Proximal (nearer)
Flexor muscles
Motor Neurons to
Distal (farther)
Flexor muscles
“Shin”
Distal (farther)
Extensor muscles
“Hamstrings”
Proximal (nearer)
Flexor muscles
“Calf” Distal (farther)
Flexor muscles
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
organized
systematically
according to the
body plan somatotopically
27
Demonstration
“Knee Jerk”
Stretch Reflex & Antagonist Inhibition
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
29
When the knee is
struck…
Ia muscle afferents fire…
there is monosynaptic
activation of the extensor
-motor neuron…
and the (agonist) muscle(s)
contracts.
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
30
When the knee is
struck…
Ia muscle afferents fire…
there is monosynaptic
activation of the extensor
-motor neuron…
and the (agonist) muscle(s)
contracts.
The knee extends.
Glycinergic (inhibitory) interneurons
are also activated…
…which inhibit motor neurons to the
flexor (antagonist) muscle.
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
31
“Stepping on a Nail”
Withdrawal & Crossed Extensor Reflexes
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
32
Stepping on a sharp
object activates pain
afferents in the skin…
activating
interneurons in the
dorsal horn…
that excite flexors and inhibit
extensors…
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
33
Stepping on a sharp
object activates pain
afferents in the skin…
activating
interneurons in the
dorsal horn…
that excite flexors and inhibit
extensors…
and the leg flexes “withdraws.”
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
34
But the person would fall…
if the crossed
extensors weren’t
activated…
and the crossed flexors
weren’t inhibited to extend the
other (contralateral) leg to
stand on.
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Pathways
• Subserve a particular function
• Axons travel together in specific locations (i.e., tracts)
in a particular order (topography)
• Always consider: cell body (soma) location, axon
course, synapses and side relative to origin and
destination
• Nomenclature often origin and target, i.e., CorticoSpinal Tract = from cortex to spinal cord
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Path Finding
• Loss of a particular function after damage (lesion)
• Stimulation (natural/electrical) with recording
• Pathology - degeneration of cells and axons with
secondary loss of myelin
• Experiments - special stains and tracers that take
advantage of physiological processes
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Pathway Conventions
• Related to whole brain through “sections” – gross,
histological, imaging
• Related to fiber bundles (fasciculi; i.e., lateral
columns, internal capsule, corpus callosum)
• Related to nuclei, ganglia, areas, layers
• Related to transmitters and effects: excitatory,
inhibitory, modulatory; fast, slower, slow
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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THE BRAIN ATLAS 3nd ed, pp. 5, 7
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
39
Pathways - “Primitive” ––––> “Evolved’
(Synapse & Synapse Number)
Intraspinal
“Pathways”
Midline
Midline
2
1
1
Knee
Jerk
Antagonist
Inhibition
1
2
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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THE BRAIN ATLAS 3nd ed, p. 8
Brainstem
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
Cerebellum
41
THE BRAIN ATLAS 3nd ed, p. 151
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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THE BRAIN ATLAS 3nd ed, p. 140
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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THE BRAIN ATLAS 3nd ed, p. 75-76
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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Dorsal Column/Medial Lemniscus (a
ribbon) Pathway
This pathway carries fine discriminative
and active touch, body and joint position,
and vibration sense.
THE BRAIN ATLAS 3nd ed, p. 185
Face
Hand
Body
Foot
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
46
Pathways - “Primitive” ––––> “Evolved”
(Synapse & Synapse Number)
Intraspinal
“Pathways”
Midline
Ascending Sensory
Pathway
Midline
Midline
2
1
2
1
1
Knee
Jerk
Antagonist
Inhibition
Dosal Column/ Medial
Lemniscus Pathway
1
2
2
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
47
Corticospinal (Pyramidal) Pathway
This is the direct connection from the
cerebral cortex for control of fine
movements in the face and distal
extremities, e.g., buttoning a jacket or
playing at trumpet.
THE BRAIN ATLAS 3nd ed, pp. 36, 43
Corticospinal Tract
(Pyramid) at Medulla
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Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
49
THE BRAIN ATLAS 3nd ed, p. 201
Foot
September 27, 2010
Hand
Face
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
All
50
THE BRAIN ATLAS 3nd ed, p. 201
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
51
Pathways - “Primitive” ––––> “Evolved’
(Synapse & Synapse Number)
Intraspinal
“Pathways”
Midline
Ascending Sensory
Pathway
Midline
Midline
Descending Motor
Pathway
Midline
2
1
2
1
1
1
Knee
Jerk
Antagonist
Inhibition
Dosal Column/ Medial
Lemniscus Pathway
Corticospinal
Pathway
1
2
2
1
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
52
The left
hemisphere
of the
monkey
brain - Motor
(Ms) and
Somatosens
ory (Sm)
maps
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
53
What this lecture was about:
Spinal Cord - Segmental organization
Peripheral Nerves - Compound action potential
(Erlanger & Gasser Prix Nobel 1944)
Spinal Nerves - Dermatomes, motor neuron pools
(nuclei) and motor units
Spinal reflexes - stretch (knee jerk); withdrawal/
crossed extensor
Introduction to Pathways - 1 sensory (DC-ML); 1
motor (CST)
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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For Review
Use the Bio 3411 Work Sheet 082809 (handout
and posted on the course web site) to get
comfortable with the neuroanatomy.
It’s neither rocket science nor is it neurosurgery, it
just takes a little practice!
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
55
The New Yorker, 7/10-17/2006, p. 110
September 27, 2010
Lecture VIII. The Spinal Cord,
Relexes and Brain Pathways
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