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NROC69H3 Lecture Notes - Motor Control, Peroxidase, Motor System

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NROB60 Study Package: Week 4
Homira Osman
Week 4: Lecture
May 27, 2008
Lecture Topics
Lecture IV
Readings: The Cytoskeleton (Pages 35 38, 40 41)
Lecture Summaries [L4]
- Different Child Brain (Part 1)
- Child Brain (Part 2)
- The Cytoskeleton
o Scaffolding
A flexible, changeable scaffold
It gives the neuron its characteristic shape
o Extends throughout the cytoplasm
o Some fibers are permanent
o Most fibers are synthesized or disassembled according to the cell‟s needs
o The “bones” of the cytoskeleton are the microtubules, microfilaments, and neurofilaments
o Elements of the cytoskeleton are dynamically regulated and are very likely in continual
NROB60 Study Package: Week 4
Homira Osman
The Cytoskeleton
- 5 important functions:
o (I) Cell shape
Provides mechanical strength
Helps determine the shape of the cell
o (II) Internal organization
Stabilize the positions of organelles
Dynamic, changing from moment to
moment in response to cell‟s needs
o (III) Intracellular transport
Transport materials into the cell
Transport materials within the
cytoplasm “railroad track”
o (IV) Assembly of cells into tissues
Connect to fibres in extracellular space
Link cells together and to supporting
material outside of cells
Mechanical strength and allow transfer
of information
o (V) Movement
Migration of white blood cells;
extension of nerve cells, allow
movement of cilia an flagella
- 20 nm in diameter
- Big
- Run longitudinally down neurites
- Appears as a straight, thick-walled, hollow pipe
- Composed of smaller strands of tubulin braided
together (pearls on a string)
- Formed through polymerization
- Regulated by various signals
o E.g.: microtubule-associated proteins (MAPs)
(neuron specific type TAU)
- Anchor the microtubules to one another and to other
parts of the neuron
- 5 nm in diameter (small) (same thickness as plasma
- Throughout neuron but more numerous in neurites
- Two thin strands of ACTIN protein braided together
- Formed through polymerization
- Constantly undergoing assembly and disassembly
- Regulated by signals in the neuron
- Running longitudinally down the core
- Anchored to the membrane by attachments with a meshwork of fibrous proteins that line the
inside of the membrane (like a spider web)
Neurofilaments (Intermediate)
- 10 nm in diameter
- Exist in all cells as intermediate filaments (only called neurofilaments in neurons)
- Composed of multiple sub-units linked together
- Appears as a straight, thick-walled, hollow pipe
- Composed of three protein strands woven together
NROB60 Study Package: Week 4
Homira Osman
- Each protein is an individual, long protein molecule
- Each protein molecule is tightly coiled in a tight, spring-like configuration
- Mechanically very strong
- Cross link within the neuron
Axons Carrying Outgoing Signals To The Target
- Axonal Transport: slow axoplasmic flow; fast anterograde vs retrograde
Axoplasmic Transport
- Proteins of the axon must be synthesized in
the soma and then shipped down the axon
- Slow Axoplasmic Transport: 1-10 mm per
- Fast Axoplasmic Transport: Up to 1000
mm per day
A mechanism for the movement of material on
the microtubules of the axon
- Trapped in membrane enclosed vesicles,
material is transported from the soma to the
axon terminal by the action of the protein
kinesin, which “walks” along mictotubules at
the expense of ATP