September 21-25 NSCI 3310
Popular in Cellular Neuroscience
Joseph Merritt Ramsey
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Popular in Neuroscience
This 5 page Class Notes was uploaded by Joseph Merritt Ramsey on Sunday September 27, 2015. The Class Notes belongs to NSCI 3310 at Tulane University taught by Jeffery Tasker in Fall 2015. Since its upload, it has received 102 views. For similar materials see Cellular Neuroscience in Neuroscience at Tulane University.
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Date Created: 09/27/15
Septem ber 25 Acton Potenta Propagaz lon o Conduction of an Action Potential 0 Interplay of Passive and Active Potentials Action potentials are generated through the balance of active and passive potentials 0 Its propagation begins at the Hillock and flows down to the Terminal 0 This process even occurs in long axons such as projections to spinal cord extending multiple feet The Hillock is the site for charge aggregation it all sums up on the hillock which is a PASSIVE process 0 Pathway of an Action Potential l Hillock o If the cell is depolarized to threshold it occurs on the Hillock o This is where each the charge from the stimuli aggregates o Passively spreads and collects 2 Initial Segment 0 Here is where the passive signaling turns into the initial action potential 0 That initial action potential leads to passive spreading and creates the Propagation down the axon 3 Next Segment 0 The passive spreading from the initial influx that diffused downstream causes depolarization at the next segment and revitalizes the signal 4 Regeneration o The process is regenerative so every time the Sodium influx passively diffuses to the next segment the full Depolarization is revitalized 0 Fires the full potential again 5 Refractory Period And its Influences o The refractory period of an Action potential prevents current from flowing backwards up the cell back to the Soma 0 During the absolute refractory period which occurs as the cell is Repolarizing so Potassium Channels are open and Sodium is lnactivated Sodium cannot enter and thus AP cannot occur 0 Figure A 1 39iqt iii in iji39l i 39s A in Mm ltgm 5 a 1 if Ci 3 Jr C if g lquotDHC 39mfl Wad muckyV E 9 C35 1 KJ 39 39 In 1 1 A r 4 l t EKLHC k i w v 0amp037 7 cw do it k f i m c v I 39 IKI If quot J g 3 S QAVA u 3 C We ex v r I W C 39 QP J I l t39 l 0 As you can see in the figure if we were to artificially introduce charge directly in the center of the cell the AP would travel up the cell because no Refractory Period is occurring This is strictly experimental and does not occur naturally But this Antidromic Current is useful for tracking neural pathways because the AP occurs in both direction and reveals all All in all the pathway for AP Propagation is a continual balance of passive and active forces and potentials o Myelination and Action Potentials Moving Down an Axon 0 Figure B ght d t aCHMEIE i Y x T mtwcts J r k 14 0 Note that the AP is sent down the axon because of charge diffusion so there are gaps noted with a as the first depolarization repolarizes and the next channels begin to open 0 Myelination widens those gaps in essence making the signal jump between the gaps called Node of Ranvier o Directional Traveling 0 Terms to Know f Orthodromic one o 39reoz 39on down the axon 39n his case 2 Antidromic baokwaro propagation 0 Back Propagation and its Role If the Charge aggregate is large enough the passively diffusing forces flow back up into the Soma and into the Dendrites I These dendrites have 1 Channels 2 Neurotransmitters and 3 Synapses 0 These factors can influence and communicate with other neurons that are upstream to the given cell 0 Axonal Antidromic Propagation vs Back Propagation I Back propagation is possible and vital to proper cell functioning ANTIDROMIC PROPAGATION ON AN AXON IS NOT 0 Conductivity Factors o f Myelination 120ms with myeinated neurons 2ms without 0 2 Diameter z ncers better I Duration a short 2m3939secono s span I Diameter Overview 0 Larger thicker diameter increases conductivity efficiency 0 Exam plesI o C5er Neurons are thin unmyeinated sensory neurons on the skin 0 Touch neurons are generally myeinated for quicker response 0 Pain receptors are thin and unmyeinated the reflex occurs before the realization ConducHon 0 Factors Influencing o Iamez er ano myeIn presence 0 Glia Cells and Their Roles I Oligodendrocytes in the CNS Central Nervous System one wraps 39z s exz ensons arouno numerous neurons n the CNS I Schwann Cells in the PNS Peripheral Nervous System eacn ce ancnors 39z sef to an axon secton and produces myeIn o Myelin I FigureC welt f t tit Till purl E r c r w t mr lrr39 r mmnrf a f1 i39quot I It separated inner and outer charges normally they rest right on the membrane but with Myelin the charges are more separated 0 They no longer collect and congregate on the whole membrane but instead on the nodes
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