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Lecture 6

Psychology 1000 Lecture 6: Synaptic Communication September 27

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Psychology 1000

Psychology 1000 September 27, 2016 Synaptic Communication How do neurons work? Neural communication The synapse Next time: The Brain Scan: p. 76-87 How do neurons produce an electrical signal? How does a neuron code intensity? How does one neuron communicate with another? how does a cell produce an electrical signal? • Neuron is like a bag of fluid with holes in it (It is semipermeable- ions able to float back and forth) • Has ions in it (Cl-, A-, K+, Na+) on inside • On outside it has ions (Na+, K+, Cl-) but outside there are many many more sodium. With the different charges, it produces an electrical charge on the cell membrane • Negative on inside relative to the outside • Neuron is like a tiny battery that is charged from the ions • If the neuron gets stimulated= action potential The action potential ***EXAM***… - Neuron just sitting there (no stimulated) it is in resting potential (negative electrical charge -70) - When it is stimulating- the wholes in the cell membrane get bigger, as it gets bigger, more ions can come in and out, and therefore the neuron can become more positive- moving more positive= depolarization Na+ inflow (coming in) - If the sodium reaches a certain point (-55)- threshold= the wholes open as wide as they can more sodium floods in and goes to +40 - Repolarization- K+ outflow - Now the neuron has to recover after +40. We start to repolarize by kicking out the potassium (pump). Potassium goes out and you drop in charge - It doesn’t stop at -70, it overdoes it (drops below resting potential), then you let things float back and it will finally go back to resting potential (-70) - Takes about 7millaseconds to get back to resting potential - Hyperpolarization- below -70 (below resting potential) - Absolute refractory period- the time between the peak of +40 and the bottom of hyperpolarization. Nothing can stimulate neuron when it is in the absolute - Relatively refractory period- you can stimulate neuron, but it takes more intense stimulus because you have to move it from -90 to back up Neural Communication - The electrical signal moves down the axon by changing the relative concentration in the axon - Action potential only happens in the axon (set off at the axon hillock, where the axon meets the cell body) - Grade potentials- in the cell body and dendrites, accumulate until they are up at a certain point Coding intensity… ➢ Neuron fires on all-or-non fashion (neurons fire or they don’t fire) ➢ Height of “spike” fixed (only stops at +40, doesn’t go up) How to code intensity? ➢ Neurons have different thresholds ➢ Strong stimulus will hit more neurons ➢ Frequency of firing- how fast the neurons fire ➢ How many neurons are stimulated? ➢ Intensity directly proportional to frequency of firing (at some point, you can’t fire it any faster- due to the absolute refractory period because nothing will happen there) How do cells communicate? Reflex arc… there’s a space between the sensory neurons and motor neurons= synapse - Sherrington’s experiment (inferring the synapse)- looking at a dog by stimulating dogs paw, how fast would it take the dog to move their paw. He called the gap the synapse - Gap between the axon and dendrite - Vesicles- do the synaptic communication. The bags of chemicals need to get across the ga
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