NEUROCYTOLOGY Sept. 2, 2009 Jennifer LaVail, Ph.D. (
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NEUROCYTOLOGY
Sept. 2, 2009
Jennifer LaVail, Ph.D.
(http://anatomy.ucsf.edu/Pages/lavaillab/index.html)
NEUROCYTOLOGYObjectives
To build on your understanding of the structure and diversity of the cells that make up the nervous system
1. Structure and function of neurons
2. Axoplasmic transport
3. Structure and function of synapses
4. Structure and function of glial cells
What kinds of cells are these?
What kinds of cells are these?
Neuron?Epithelial cell?Glial cell?
The neuron has the same biochemistry and complement of organelles as other cells of the body.
What makes a neuron special?
But, neurons are remarkable for their polarity.
Structurally the two most distinctive features of the neuron are its polarized shape and localized secretory function.
Action potential
Polarized shape -
Action potential
The axon requires unusual modifications of the cytoskeleton and specializedintracellular transport mechanisms.
Among all the cells inour body, only neuronshave axons.
Microtubule polarity
Fibroblasts have continuous µts. Neurons have multiple µts.Fibroblasts have unipolar µts. Axons have unipolar µts. Dendritic µts have mixed polarity.
Microtubule polarity
Soma
The neuron cell body is the primary location of protein synthesis.
Most of the proteins for axon maintenance and synaptic functionhave to be transported to the axon.
Where is the cell body?
Electron micrograph of a neuronal cell bodyCytoplasm = pink; nucleus = yellow
What is specialabout this neuroncell body?
Electron micrograph of Nissl bodies (stacks of RER) “protein synthesis machines”
DRG axon hillock
Neuron cell body also has polarity axon hillock - region with no ribosomes…beginning of the
axon.
DendritesInput region of neuron
Form of energy varies, e.g.,chemical, stretch, thermal, neurochemical.Integrates excitatory and inhibitorysynaptic inputs.
Dendrites pyramidal-Purkinje
Principal structures of a neuron
Cell BodyDendritesAxon hillockInitial SegmentAxonSynaptic terminals
Blowfly neuron
processes
Pyramidal neuron, rat cerebral cortex
Motoneuron axons grow long distances to muscle endplateso
The structure of chemical synapses
Neuromuscular junction in Lateral rectus muscle
Motor end plate 2
Chemical Synapse
Voltage-sensitivecalcium channels
Synaptic cleft15-100 nm
Synaptic components:
Synaptic vesiclesPresynaptic membraneSynaptic cleftPostsynaptic membrane
CNS synapses
synapse
Two large synaptic terminals containing mitochondria contacting a dendrite
A synaptic terminal containing dense cored vesicle indicating the presence of catecholamine transmitters
A large dendrite and spine contacted by many synaptic boutons
Distinguishing characteristics of axons and dendrites
Characteristic Axon Dendrite
Ontogeny develops early develops later
Length several µm to >1 m limited
Size/Shape 0.1 to 20 µm 0.1 – 5 µmuniform diameter tapered
Axon hillock present absent
RER absent present
Cytoplasm vol. 100 x greater relatively little
Number per neuron 1 > 1
Excitability conducts AP passive spread
Myelin present on axons rare but glial wrap >than 1 um
Major Point: Mature axon has no RER, ribosomes, Golgi, so no way to make proteins. Proteins have to be transported into and along axon.
Neuron cell body ~100 µm
Axon 7
ft
2.13 x
107
Differentiating neuronal cells (actin, microtubules and DNA)
Torsten Wittman
Motile embryonic neuronEmbryonic neurons move, axons grow.
The components of axonal transport
microtubules
cargo
motor
Cargo comprised of protein, peptides, proteoglycans and amino acids.Most are transported within organelles. (No synaptic vesicle transport).Rates are about 200-400 mm/day or much slower, 1-2 mm/day.Bidirectional movement depends on balance of cytoplasmic motors.
Axonal transport
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Real time assays of viral transport
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
Anterograde transport of HSV
Axonal transport of virusHSV transport
The myelin sheath along a myelinated CNS axon is composed of sections of myelin made from a number of individual cells
Remember, however, not all axons are myelinated. Small diameter axons generally have no myelin covering.
In the PNS axons less than 1 µm in diameter are unmyelinated.
Axon PNS
RELATIVE SIZES
Structure (mm) µm nm
Visual Cortex (thickness) 5Cortical column (thickness) 0.25 250Neuron cell body 15-100Red blood cell 7Neuromuscular junction 2-4Sympathetic axon 0.2 200CNS synaptic bouton 0.5-2.0 500-2000Dense core synaptic vesicle 100Synaptic vesicle 50Smooth endoplasmic reticulum 5
sizes