Neuroscience and Behavior

- Basic premise: everything psychological is simultaneously biological

- Behavior, thought, mood, etc... is the product of activity among billions and billions of interconnected cells called neurons.

___________ myelin sheath terminal branches of axon
__________| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||/-------------<
__________|cell body |­­­­­­­­­­­­­­­­­­_____axon _______________________-----------------<
__________|___________|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||\__________
dendrites ->->neural impulses->->

- How do neurons communicate? - Each neuron contains: - a cell body - two types of branching fibers - dendrites: receive messages from other cells and pass it to the cell body - short bushes of fiber - axon: passes neural message (information) from the cell body and passes it to the other neurons, muscles or glands - can be short or long (e.g. short in brain, long in leg) - extensions of the neuron - usually end in terminal branch - many axons are covered in a fatty substance, called myelin (the myelin sheath) - increases speed of neural message traveling along the axon (neural conduction) - as you get older, you get more and more myelin - cells with no myelin = gray matter, cells with myelin = white matter - Multiple Sclerosis - decay of the myelin - causes lots of problems: loss of motor and mental abilities

How do neurons work? - the neuron fires a brief electrical impulse when stimulated by heat, light, sound, pressure, chemicals, etc. (e.g. you put your finger near a flame) - the impulse is called an action potential - Occurs in one part of the neuron, then travels the length of the neuron (down the axon) to the next cell - the brain is bathed in salt water - inside and outside each cell are ions (charged particles)

+ + + sodium and chloride + + + (outside axon) - - - - potassium- - - - - - - (inside axon) + + + sodium and chloride + + + (outside axon)

- when the cell is at rest, the inside o f the cell is more negatively charged than the outside, because the positively charged sodium ions are kept outside the cell
- the cell becomes less negative when stimulated, because channels in the cell open up allowing positive sodium ions outside to flow inside -> this causes the cell to depolarize -> if it depolarizes enough, It triggers an action potential

- e.g. + + + + + + + + + - - - - + + + + + + - - - - - - - - - - - - - -> + + + + + - - - - - - - + + + + + + + + + + - - - - - - - + + + + +

-once a cell depolarizes in one part, it triggers the next part to open its sodium channels to depolarize that part
- this carries the action potential down the length of the cell
- an action potential in one part of the cell triggers succeeding action potentials in adjacent parts of the cell, which is how the neural message is carried along the cell - after the action potential: pumps move the sodium outside and the potassium inside so the cell is polarized once again

- How does a message communicate with the next cell?
- the axon terminals of the sending cell are filled with round sacks (vesicles) which contain a chemical (neurotransmitter) - an action potential causes the vesicles to move down the terminal fibers and release the neurotransmitter
- the axon terminals of the sending cell almost but not quite touch the surface of the receiving cell - the gap is called a synapse
- the neurotransmitter travels across the synapse into the receptors in the dendrites of the next cell

The axon terminals of one cell almost, but not quite, tough the surface of another cell
- the gap is called the synapse
- when an action potential reaches the axon terminal, the