Neural signaling + ch 9 notes
Neural signaling + ch 9 notes PSYCH 50
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This 3 page Class Notes was uploaded by Emily Wu on Sunday March 6, 2016. The Class Notes belongs to PSYCH 50 at Stanford University taught by Justin Gardner in Winter 2016. Since its upload, it has received 24 views. For similar materials see Intro to Cognitive Neuroscience in Psychlogy at Stanford University.
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Date Created: 03/06/16
Appendix: Synaptic Transmission ● presynaptic element a specialized region on the axon terminal that conveys the neural signal ● postsynaptic element a site on the target cell’s dendrite or cell body that receives the neural signal Electrical synapses ● current flows from presynaptic neuron into postsynaptic neuron ● pre and post synaptic neurons are linked gap junction ● gap junction contains specially aligned ion channels that allow ions to pass through ● transmission across gap junction can go either way and is really fast Chemical synapses ● space between pre and postsynaptic neurons is callynaptic cle; space is much larger than a gap junction ● presynaptic neuron hasvesicle: small spheres, membranebounded, contains neurotransmitters ● transmission sequence: ○ action potential reaches axon terminal ○ voltagegated calcium ion channels open ○ influx of Ca2+ into presynaptic terminal ○ causes vesicles to fuse with synaptic membrane and empty the neurotransmitters into synaptic cleft ○ transmitters diffuse across cleft and bind to receptors on membrane of postsynaptic neuron ○ alters the opening/closing of ion channels in postsynaptic neuron → either increases or decreases probability that postsynaptic neuron will fire an action potential ○ reuptake of neurotransmitters back into the presynaptic cell Neurotransmitters ● classified into: ● small molecule neurotransmitteroften individual amino acids ○ glutamate: excitatory ○ GABA: inhibitory ○ acetylcholine: excitatory ○ ATP: excitatory ○ serotonin, dopamine, histamine ● neuropeptides larger proteins made of 336 amino acids Receptors ● classified into: ○ ionotropic receptorslinked directly to ion channels ■ contains an extracellular site that binds neurotransmitters, and membranespanning domain that creates an ion channel ■ combines neurotransmitter binding and ion channel functions ■ made up of several units ■ create rapid postsynaptic potentials ○ metabotropic receptors activate ion channels by activation of intermediate called Gprotein ■ contains extracellular site that binds neurotransmitters and intracellular site that binds G proteins ■ binding of neurotransmitter → binding and activation of G protein → G protein interacts directly with ion channels or other proteins ■ consist of single units ■ create slower postsynaptic potentials Glutamate ● important for brain function ● nearly all excitatory neurons in central nervous system are activated by glutamate ● can’t cross bloodbrain barrier, so must be synthesized from chemicals already present ○ glutamine (released by glial cells) is precursor ○ glutamine is taken up by presynaptic neurons and metabolized into glutamate ○ glutamate is released into synaptic cleft → then taken up by glia → turned back into glutamine → transported out of axon terminal ● receptors are all excitatory Excitatory and Inhibitory Postsynaptic Potentials ● excitatory postsynaptic potential (EPSincrease likelihood of action potential firing in postsynaptic cell ● inhibitory postsynaptic potential (IPdecrease likelihood of action potential firing ● reversal potentia the current that underlies the postsynaptic potential ● if reversal potential is more positive and exceeds action potential threshold, excitatory response is generated ● if reversal potential is more negative than action potential threshold, inhibitory response is generated ● a neuron is innervated by thousands of synapses, so it takes summation of all postsynaptic potentials to influence action potential generation Chapter 9: Declarative Memory Introductory Box ● HM gets amnesia because of removal of medial temporal lobes ● unable to form new memories (episodic memory) ● unable to learn new facts (semantic memory) ● hippocampal damage in some children resulted in impaired episodic memory but can retain semantic memory/learn new facts, perceptual and working memory abilities intact ● hippocampus specifically associated with episodic memory but not semantic memory Box 9B ● fMRI can distinguish between encoding and retrieval in episodic memory ● subsequent memory paradigm : using event related potentials to compare between successful/unsuccessful trials during encoding or retrieval of memory ● successful encoding produces greater activity than for trials where stimulus was forgotten → subsequent memory effect → tend to be seen over frontoparietal regions Box 9C ● recalling new and old items show different activity in event related potentials ● first: 300500ms after new stimulus is presented, new items elicit greater voltage over midfrontal regions than old items ● second: 400800ms after stimulus, old items elicit more positive voltage over parietal electrodes than new items → left parietal effect ○ effect more pronounced for more complex levels of recollection ○ leftlateralized for verbal materials ○ effect is greater for deeply encoded than shallowly encoded items ● third: 6001200 ms after stimulus, old items elicit more positive voltage over right frontal regions than new items → right frontal effect
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