lecture viii. the spinal cord, reflexes and brain pathways bio 3411 monday september 27, 2010
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What the last Lecture was about September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 3 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 systemTRANSCRIPT
Lecture VIII. The Spinal Cord, Reflexes and Brain Pathways
Bio 3411 Monday
September 27, 2010
September 27, 2010 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways
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ReadingsNEUROSCIENCE 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, 16.14Read Chapter 17 pp. 432–436
Study figure 17.9
THE BRAIN ATLAS 3rd ed:Read pp. 4-17 on class web siteLook at pp 36, 43, 49, 75-76, 140, 151, 154, 170-171, 182-183, 200-201.
What the last Lecture was about
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• 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
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Overview for this LectureSpinal Cord
Columns, Horns, Spinal Segments Spinal Nerves
Dermatomes, Motor Units
Reflexes“Knee Jerk”- Myotatic or Stretch ReflexWithdrawal & Crossed Extensor Reflexes
Two Spinal PathwaysSensory - Dorsal Column/ Medial lemniscusMotor - Cortico-spinal Tract
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Segments of spinal cord, spinal nerves and vertebrae
Cervical (C) - Neck
Thoracic (T) - Chest
Lumbar (L) - Back
Sacral (S) - Pelvis
(The Brain Atlas 3rd ed, p. 8)
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Human spinal cord from side, front and back
≈ 50 cm
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Internal Structure• Canal = tube
• White Matter - columns, tractsanterior 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”
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Section of human spinal cord (C8) myelin stain
Back (posterior/dorsal)
Front (anterior/ventral)
Anterior Horn (gray
matter)
PosteriorHorn (gray
matter)Posterior Column (white matter)
Anterior Column (white matter)
Lateral Column
(white matter)
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Section of human spinal cord (C8) cell body stain
Anterior
Horn
Posterior
Horn
Posterior
Column
Anterior
Column
Lateral
Column
Back (posterior/dorsal)
Front (anterior/ventral)
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Sacral Cord (The Brain Atlas 3rd ed, p.154)
Cervical Cord (The Brain Atlas 3rd ed, p.151)
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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Spinal Nerves
• Intervertebral foramen
• Segmental spinal nerve
• Compound action potential
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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).
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Mixed spinal nerve
Periphery (skin, muscle,
etc.)
Segmental nerve: (posterior (dorsal) root = sensory - touch; anterior (ventral) root = motor -movement; spinal or posterior
(dorsal) root ganglion = sensory nerve cell bodies)
Spinal cord
back = posterior
front = anterior
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Joseph Erlanger
1874 - 1965
(Prix Nobel 1944)
Herbert Spencer Gasser
1888 - 1965
(Prix Nobel 1944)
George H. Bishop
1889 - 1973
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Periphery (skin, muscle, etc.) Spinal cord
front = anterior
back = posterior
Mixed spinal nerve
Stimulate (Shock) Record
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Compound action potentialErlanger, Gasser (Bishop)
Conduction Velocity m/s
Discriminative Touch
Fast pain & Temperature (cold)
Slow pain & Temperature (warm)
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Cross section of human muscle (motor) nerve – myelin stain
Cross section of human sensory nerve – myelin stain
Axon diameters differ in motor and sensory nerves
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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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Spinal or Posterior (dorsal) Root Ganglion Cells
Pseudo-Unipolar Neurons(neurons start as bipolar cells and become “unipolar” during development)
Single sensory endingslight & crude touch, pain, temperature and muscle senses
Axons diverge to multiple spinal targets motor neurons - c, interneurons - c, spinal cord - b, and brain -a
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Periphery (skin, muscle,
etc.)
Segmental nerve (posterior (dorsal) root = sensory - touch; ventral root = motor -movement; spinal or posterior (dorsal) root ganglion =
sensory nerve cell bodies)
Spinal cord
back = dorsal
front = ventralMixed spinal nerve
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Dermatome =
The region (slice) of skin innervated by a single spinal or posterior (dorsal) root ganglion
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Motor Units, Motor Neuron
Pools & Somatotopy
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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 cellsspinal interneuronslong tracts from from brain
• Integrate• Map
flexors, extensors, proximal, distal
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Section of human spinal cord (C8) myelin stain – anterior horn
Section of human spinal cord (C8) cell body stain – anterior horn
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Motor Unit - A motor
neuron and the muscle
fibers it innervates.
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Motor neuron
pools (nuclei) are
organized
systematically
according to the
body plan -
somatotopically
Motor Neurons to Proximal (nearer) Flexor muscles
Motor Neurons to Proximal (nearer) Extensor musclesMotor Neurons to
Distal (farther) Extensor muscles
Motor Neurons to Distal (farther) Flexor muscles
“Quads” Proximal (nearer) Extensor muscles
“Shin” Distal (farther) Extensor muscles
“Hamstrings”Proximal (nearer) Flexor muscles
“Calf” Distal (farther) Flexor muscles
Demonstration
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“Knee Jerk”Stretch Reflex & Antagonist Inhibition
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When the knee is struck…
Ia muscle afferents fire…
there is monosynaptic activation of the extensor -motor neuron…
and the (agonist) muscle(s) contracts.
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…which inhibit motor neurons to the flexor (antagonist) muscle.
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…
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“Stepping on a Nail” Withdrawal & Crossed Extensor Reflexes
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that excite flexors and inhibit extensors…
Stepping on a sharp object activates pain afferents in the skin…
activating interneurons in the dorsal horn…
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and the leg flexes “withdraws.”
that excite flexors and inhibit extensors…
Stepping on a sharp object activates pain afferents in the skin…
activating interneurons in the dorsal horn…
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and the crossed flexors weren’t inhibited to extend the other (contralateral) leg to stand on.
if the crossed extensors weren’t activated…
But the person would fall…
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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., Cortico-Spinal Tract = from cortex to spinal cord
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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
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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
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THE BRAIN ATLAS 3nd ed, pp. 5, 7
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Midline Midline
Knee Jerk
1
Antagonist Inhibition
2
Intraspinal “Pathways”
1 1
Pathways - “Primitive” ––––> “Evolved’ (Synapse & Synapse Number)
2
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Brainstem Cerebellum
THE BRAIN ATLAS 3nd ed, p. 8
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THE BRAIN ATLAS 3nd ed, p. 151
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THE BRAIN ATLAS 3nd ed, p. 140
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THE BRAIN ATLAS 3nd ed, p. 75-76
Dorsal Column/Medial Lemniscus (a ribbon) PathwayThis pathway carries fine discriminative and active touch, body and joint position, and vibration sense.
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THE BRAIN ATLAS 3nd ed, p. 185
Foot
Hand
Face
Body
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Midline Midline Midline
Knee Jerk
1
Antagonist Inhibition
2
Dosal Column/ Medial Lemniscus Pathway
2
Intraspinal “Pathways”
Ascending Sensory Pathway
1 1
1
2
2
Pathways - “Primitive” ––––> “Evolved” (Synapse & Synapse Number)
Corticospinal (Pyramidal) PathwayThis 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.
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THE BRAIN ATLAS 3nd ed, pp. 36, 43
Corticospinal Tract (Pyramid) at Medulla
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THE BRAIN ATLAS 3nd ed, p. 201Foot Hand Face All
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THE BRAIN ATLAS 3nd ed, p. 201
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Midline Midline Midline Midline
Knee Jerk
1
Antagonist Inhibition
2
Dosal Column/ Medial Lemniscus Pathway
2
Corticospinal Pathway
1
Intraspinal “Pathways”
Ascending Sensory Pathway
Descending Motor Pathway
1 1 1
1
2
2
Pathways - “Primitive” ––––> “Evolved’ (Synapse & Synapse Number)
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The left
hemisphere
of the
monkey
brain - Motor
(Ms) and
Somatosens
ory (Sm)
maps
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What this lecture was about:Spinal Cord - Segmental organizationPeripheral Nerves - Compound action potential
(Erlanger & Gasser Prix Nobel 1944)Spinal Nerves - Dermatomes, motor neuron pools
(nuclei) and motor unitsSpinal reflexes - stretch (knee jerk); withdrawal/
crossed extensorIntroduction to Pathways - 1 sensory (DC-ML); 1
motor (CST)
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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!
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The New Yorker, 7/10-17/2006, p. 110