Mind, Brain & Behavior

1. Mind, Brain & Behavior Monday January 13, 2003

2. 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

3. Nerve Cells & Behavior Chapter 2 Pg 21-28

4. Two Kinds of Cells • Neurons (nerve cells) – signaling units • Glia (glial cells) – supporting elements: • 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

5. 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.

6. Parts of the Neuron • Soma – the cell body • Neurites – two kinds of extensions (processes) from the cell: • Axon • Dendrites • All parts of the cell are made up of protein molecules of different kinds.

7. How Neurons Communicate • An electrical signal, called an action potential, travels down the axon. • 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.

8. How to Tell Axons from Dendrites • 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.

9. Ramon y Cajal’s Principles • Principle of dynamic polarization – electrical signals flow in only one, predictable direction within the neuron. • Principle of connectional specificity: • 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.

10. Ways of Classifying Neurons • By the number of neurites (processes): • Unipolar, bipolar, multipolar • By the type of dendrites: • Pyramidal & stellate (star-shaped) • By their connections (function) • Sensory, motor, relay interneurons, local interneurons • By neurotransmitter – by their chemistry

11. 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.

12. Organelles • 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

13. Kinds of Glia • Oligodendrocytes – surround neurons and give them support. • 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.