cytology nikon © dent/obhs 131 neuroscience. reticular theory 1886: golgi-techniques 1888: ramon y...
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Cytology Nikon ©
DENT/OBHS 131Neuroscience
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reticular theory1886: Golgi-techniques
1888: Ramon y Cajal1897: Sherrington
Building blocks
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Learning Objectives
Compare and contrast the morphology & function of neurons and glial cells
Explain neuronal polarization in terms of information signaling
Be able to give reasons for the energetic demands of neurons
Discuss the different roles of different categories of glial cells
Describe the relationship of neurons and glia with respect to synaptic signaling and action potential propagation
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What are the most important types of cells in the brain?
1. Neurons
2. Glia
3. Neither neurons nor glia
4. Other cells
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Types of cell
Neurons - nerve cells 100 billion
Glial cells ≈ 10 X neurons
50:50 volumeCNS vs PNS
autonomic (week 10) motor & sensory (weeks 5-8)
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Learning Objective #2
Explain neuronal polarization in terms of information signaling
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Basic function of a neuron
Transmit information from here to there
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Parts of a neuron
Dendrites receive information
Soma synthesize stuff electrical integration
Axon information conduction
Axon terminal transmit information
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En masse
Segregationwhitegray
Gross lab(week 2)
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Same but different
Multipolar (typical)single axonmultiple dendrites
BipolarPseudo-unipolar
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What type of cell is the large neuron?
1. Purkinje
2. Pyramidal
3. Granule
4. Motor
10
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Pseudounipolar neurons….
single axon - bifurcatesclassical example - sensory fibers
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Classes of neurons
SensoryMotorInterneuronsProjection
somatosensory (weeks 5-6) sensory-motor integration (week 6)
motor (weeks 7-8)
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Synapses
Dendritic shafts / spinesinhibitory / excitatory(weeks 3-4)
synaptotagmin
MAP2
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Axons are long
≈ 5ft motor neuron (e.g. Sciatic nerve)
≈99% cytoplasmHow to accomplish fast signaling (week 3)?
How to maintain structure?How to communicate between distant parts?
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Cytoskeleton
axon growth cone
(Ken Balazovich)
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Cross section of dendrite
Neurofilaments filamentous actin
Microtubules Tubulin (10% brain protein)
substrate for axonal transport
MAPs e.g. Tau (weeks 10-
11)
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Active transport
Slow:few mm / day
Fast< 400 mm /day
RetroAntero
kinesin dynein
molecular motors
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Ribosomes: Nissl substance
In dendrites (not largely in axons)may offset long transport distances in axons
Local protein synthesis at the base of spines - plasticity (weeks 10-11)
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Leaching Objective #3
Be able to give reasons for the energetic demands of neurons
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High energy use
30-40 % total energy consumption at rest Maintain ionic gradients (ion-exchange pumps) Protein synthesis Axonal transport
Mitochondria Site of oxidative metabolism - ATP Brain exclusively dependent on glucose
Found throughout the perikaryon, dendrites, spines, axons and in synaptic terminals
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Other organelles
Similar to other cells
Nucleus: only a few 1000 CNS specific genes - encode CNS proteins
extensive RNA splicing
Golgi: post-translational modification
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Relationship to other cells
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Brain Glue
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Special properties of glia?
Compared to neurons: (Astrocytes) star-shaped & largely lack polarity
No synapses - cells communicate through gap-junctions
Relatively low energy requirement; function well under anaerobic conditions
phalloidintubulinDAPI
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Learning Objective #4
Discuss the different roles of different categories of glial cells
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Key roles of glia
Remove glutamate and other amino-acids from extracellular space: de-toxify the brain
Form myelin to insulate axonsServe numerous homeostatic functions
Can and do proliferate postnatally
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Classification
Radial glia - development (next session)
Astrocyte protoplasmic astrocyte (Type 1) fibrous astrocyte (Type 2)
Schwann cell Oligodendrocyte
Macroglia <=> Microglia
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Microglia
engulfing a dying oligodendrocyte:
phagocytotic cells in the nervous system
blood derived cells comparable to macrophages
remove debris from the brain following injury and constitute an important defense system against pathogens.
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Radial glia
Development (week 1)
neuronal guidance
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Learning Objective #5
Describe the relationship of neurons and glia with respect to synaptic signaling and action potential propagation
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Schwann cell
Myelination in the PNS
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Myelin sheet
One-to-one
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Gap junctions and disease
Charcot-Marie-Tooth diseaseprogressive loss of PNS axons - weakness, atrophy
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Nodes of Ranvier
fast AP propagation (week 3)
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Oligodendrocytes
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1:10 to 1:50
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Unmyelinated CNS fibers
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CNS vs. PNS summary
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Astrocytic end feet……
contact blood vessels
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Astrocytic endfoot
Induce the blood-brain-barrier
Active transport
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From here to there…..
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Buffering of extracellular ions
Extracellular space is very narrow=> small ionic fluxes cause large concentration changes
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Astrocytes are not really star-shaped
non-overlapping
space-filling
(Bushong et al., 2002)
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Transmitter “shuttle”
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Nervous system regeneration
The CNS does not regenerate while the PNS does
This is NOT due to differences in central
and peripheral neurons but due to differences in their glia
CNS oligodendrocytes actively suppress regeneration reactive gliosis
PNS Schwann cells promote it
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Glia versus neuron - difference?excitability
(Bergles et al., 1997)