Download Cytology

Cytology
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Types of cell
Neurons - nerve cells
 100 billion
Glial cells
 ≈ 10 X neurons
50:50 volume
CNS vs PNS
Neuronal overview
Basic function of a neuron
 Transmit information from one place to another
Requirements:
 Structural
 Functional
Neurons are polarized
Parts of a neuron
 Dendrites
 receive information
 Soma
 synthesize stuff
 electrical integration
 Axon
 information conduction
 Axon terminal
 transmit information
En masse
Segregation:
 white
 gray
Same but different
Multipolar (typical)
 single axon
 multiple dendrites
Bipolar
Pseudo-unipolar
Pseudounipolar neurons….
….are really bipolar
Classes of neurons
Sensory
Motor
Interneurons
Projection
Week 6 - somatosensation
Week 7 - motor
Synapses
Dendritic shafts / spines
inhibitory / excitatory
(Week 4)
MAP2
synaptotagmin
Axons are long
≈ 5ft motor neuron (Sciatic nerve)
≈99% cytoplasm
 How to accomplish fast signaling (week 4)?
 How to maintain structure?
 How to communicate between distant parts?
Axon growth cone
Cytoskeleton
(Ken Balazovich)
Cross section of dendrite
 Neurofilaments
 filamentous actin
 Microtubules
 Tubulin (10% brain protein)
 substrate for axonal transport
 MAPs
Active transport
Slow:
molecular motors
 few mm / day
Fast
 < 400 mm /day
Retro
Antero
kinesin
dynein
Ribosomes: Nissl substance
In dendrites (not largely in axons)
Local protein synthesis at the base of
spines - plasticity
(week 9)
High energy use
 30-40 % total energy consumption at rest
 Maintain ionic gradients
 Protein synthesis
 Axonal transport
 Mitochondria
 Site of oxidative metabolism - ATP
 Brain exclusively dependent on glucose
 Found throughout the perikaryon, dendrites,
axons and in synaptic terminals
Other organelles
Similar to other cells
 Nucleus:
 Only a few 1000 CNS
specific genes - encode
CNS proteins
 Extensive RNA splicing
 Golgi:
 post-translational
modification
Relationship to other cells
Brain Glue
Glial cells
 Types
 Roles
 Phalloidin
 Tubulin
 DAPI
Special properties
 (Astrocytes) star-shaped & largely lack polarity?
 No synapses but cells communicate through gap-junctions
 Relatively low energy requirement; function well under
anaerobic conditions
•
•
•
•
Remove glutamate and other amino-acids from
extracellular space - de-toxify the brain
Form myelin to insulate axons
Serve numerous homeostatic functions
Can and do proliferate postnatally; tumors
Are astrocytes really star-shaped?
(Bushong et al., 2002)
Classification
Macroglia <=> Microglia
 Astrocyte
 protoplasmic astrocyte (Type 1)
 fibrous astrocyte (Type 2)

Radial glia - development (week 4)

Oligodendrocyte

Schwann cell
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.
Radial glia
Development
neuronal
guidance
Schwann cell
Myelination in
the PNS
Myelin sheet
One-to-one
Gap junctions and disease
 Charcot-Marie-Tooth disease
 progressive loss of PNS axons - weakness,
atrophy
Nodes of Ranvier
Saltatory conduction (week 4)
Oligodendrocytes
1:10 to 1:50
Unmyelinated CNS fibers
End feet……
contacting blood vessels
Induce the blood-brain-barrier
Active
transport
Astrocytic endfoot
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
 PNS Schwann cells promote it
Injury to the CNS
Reactive gliosis
Degenerating Neuron
Microglia
Buffering of extracellular ions
 Extracellular space is very narrow
=> small ionic fluxes cause large concentration changes
From here to there…..
Territorial coverage
non-overlapping
(Bushong et al., 2002)
Astrocytic Glutamate transport
Around synapses
Transmitter “shuttle”
Glia versus neuron - difference?
 excitability
(Bergles et al., 1997)