Transcript Mind, Brain & Behavior

Mind, Brain & Behavior
Monday
January 13, 2003
Interview with Rodney Brooks
Human as machine, machine as human:
http://www.aaai.org/AITopics/html/show.html
http://news.bbc.co.uk/olmedia/cta/progs/02/hardtalk/brooks19aug.ram
Nerve Cells & Behavior
Chapter 2
Pg 21-28
Two Kinds of Cells
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Neurons (nerve cells) – signaling units
Glia (glial cells) – supporting elements:
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Separate and insulate groups of neurons
Produce myelin for the axons of neurons
Scavengers, removing debris after injury
Buffer and maintain potassium ion concentrations
Guide migration of neurons during development
Create blood-brain barrier, nourish neurons
Neuronal Circuits
Neurons send and receive messages.
 Neurons are linked in pathways called
“circuits”
 The brain consists of a few patterns of circuits
with many minor variations.
 Circuits can connect a few to 10,000+ neurons.
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Parts of the Neuron
Soma – the cell body
 Neurites – two kinds of extensions (processes)
from the cell:
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Axon
 Dendrites
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All parts of the cell are made up of protein
molecules of different kinds.
How Neurons Communicate
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An electrical signal, called an action potential,
travels down the axon.
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An action potential is an all-or-nothing signal.
The amplitude (size) of the action potential stays
constant because the signal is regenerated.
The speed of the action potential is determined by
the size of the axon.
Action potentials are highly stereotyped (very
similar) throughout the brain.
How to Tell Axons from Dendrites
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Dendrites receive signals – axons send them.
There are hundreds of dendrites but usually just one
axon.
Axons can be very long (> 1 m) while dendrites are <
2 mm.
Axons have the same diameter the entire length –
dendrites taper.
Axons have terminals (synapses) and no ribosomes.
Dendrites have spines (punching bags).
Don’t be fooled by the branches – both have them.
Ramon y Cajal’s Principles
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Principle of dynamic polarization – electrical
signals flow in only one, predictable direction
within the neuron.
Principle of connectional specificity:
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Neurons are not connected to each other, but are
separated by a small gap (synaptic cleft).
Neurons communicate with specific other
neurons in organized networks – not randomly.
Ways of Classifying Neurons
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By the number of neurites (processes):
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By the type of dendrites:
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Pyramidal & stellate (star-shaped)
By their connections (function)
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Unipolar, bipolar, multipolar
Sensory, motor, relay interneurons, local
interneurons
By neurotransmitter – by their chemistry
Parts of the Soma (Cell Body)
Nucleus – stores genes of the cell (DNA)
 Organelles – synthesize the proteins of the cell
 Cytosol – fluid inside cell
 Plasmic membrane – wall of the cell
separating it from the fluid outside the cell.
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Organelles
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Mitochondria – provide energy
Microtubules – give the cell structure
Rough endoplasmic reticulum – produces proteins needed
to carry out cell functioning
Ribosomes – produce neurotransmitter proteins
Smooth endoplasmic reticulum – packages
neurotransmitter in synaptic vesicles
Golgi apparatus – Part of the smooth endoplasmic
reticulum that sorts proteins for delivery to the axon and
dendrites
Kinds of Glia
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Oligodendrocytes – surround neurons and
give them support.
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In white matter, provides myelination
In gray matter, surround cell bodies
Schwann cells – provide the myelin sheath for
peripheral neurons (1 mm long).
Astrocytes – absorb potassium, perhaps
nutritive because endfeet contact capillaries
(blood vessels), form blood-brain barrier.