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UAB BY 116 - Nerve Impulses

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BY 116 1st Edition Lecture 8 Outline of Last Lecture I. Neuronal PhysiologyA. Neural reflux contains CNS and PNSB. What are we communicating?C. 3 parts of the brainD. Efferent neuronsE. Variety of Reflexes and Cannon’s PostulatesF. Neural ImpulseOutline of Current LectureII. Membrane Chemical PotentialHow do polar ions move across membrane?Resting potentialGraded PotentialAction PotentialCurrent LectureII. Membrane Chemical Potential How do polar ions move across membrane? Facilitated diffusion = negative change in energy Active transport= positive change in energy- Na/K pump uses this to create -70mV resting potentialResting potential = -70mV in sample cell, created by movement of ionssecretion- means “move out” either a mechanism/ processs or ExocytosisDendrites receive the information (are sensory neurons)- makes sense that they have the most variety in the sensoryNerves energies- are changes to Resting Membrane PotentialDendritic Receptors +Enviromental stimulus = Nerve energyReceptor Potential Concept – More receptors = More sensitivityExamplesLight Force is from photons emitted from light source and received by photoreceptors in the PNSChemical Force, in the PNS are received by chemoreceptors and the CNS received by neurotransmittersGraded Potential**must achieve enough energy to start impulse, otherwise can not do anythingOrigin- contact of stimulus with dendrite Strength of GP dependent on:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Chemical gradient Duration- how long the channels are openPolarity change Depolarization- is positive, excitatoryHyperpolarization- negative, inhibitory Threshold- reaches change in polarity that allows impulse to occur, there is no turning back from this point Subthreshold- any impulse that does not reach threshold and the signal will not be sent Sensitivity/ Adaptability(means ability to turn signal off)Phasic: on/off- quickly adapting signal, responding or turning the signal off fast.deals with change in strength of stimulus Tonic: always on because the stimulus is always presentcritical, because dealing with salt and nutrient supply in the body amplitude varies slow to adapt Subthreshold signalingSignals move toward or away from threshold – ones that move toward create an action potential and those away, nothing will occursubthreshold signal- if have an excitatory signal that doesn’t make it to thresholdStrength of the graded potential when it reaches threshold determines the speed of the movement The farther the signal moves from the dendrite, the weaker the signal gets Types of post-synaptic potentials EPSP (excitatory post-synaptic potential) – cause increase in the signal to reach threshold IPSP (inhibitory) – hyperpolarizing, bringing the signal away from threshold Threshold- the point of no return from the stimulus EPSPs- Two ways of reaching thresholdOne, strong, large stimulus Summationtemporal summation- stimulus is the same weak strength but applying fast, so it adds upspatial summation- stimulus is the same kind from different places at the same time to add upIPSP- will push the signal farther from threshold (negative signal) or inhibiting reaching threshold and not allowing action potential to occurHow does the receptor potential determine our sensitivity? either reach threshold or not, there is a an all or none response to signals Adaptability= can desensitize and remove neurons from surfacedepressionLTP- long term potentiationAction Potential- massive change and restorationTrigger zone = Threshold = Action Potential at Axon hillockSignal must be sufficient in strength at Axon Hillock +60= equilibrium potential for Na, cell dies here so can not hit this number– 80 = equilibrium potential for K+rapid change in resting potential Action potential sequence:-70 = Resting Potential -70 to -55 = EPSP -55 = Activation gate of Na+ opens – Depolarization and Na+ floods in -55 to +30 = Depolarization while the K+ activation gate slowly opens+30 = Inactivation gate of Na+ closes and stops influx of sodium, however, its activation gate is still open. K+ activation gate is fully opened +30 to -90 = Repolarizing, efflux of K+, half way through here, Na+ activation gate closes, allowing for another Action Potential to occur if have enough stimulus -90 = hyperpolarizationReasons for Repolarizing with K+If let Cl- in ( NOT good because the cell becomes hyperosmotic or hypotonic, which leads to cell death, lysing If pump Na+ out ( NOT good because pump 3Na+ out for every 2K+ in, only moving one positive charge here for a high energy cost, one ATP each time! This is also extremely slowDump out K+( YES, it is FAST so you can have another Action Potential quickly Refractory periods Absolute refractory- impossible to have another AP here can not open any more Na+ channels, they are all fully opened hereActivation gate is not closed until partially back to resting potential Relative refractory- can open the channel again with strong enough stimulus Action potential (all or none response) – split into 3 areas or regionsRefractory- any area that could be reactivated Active- Absolute refractory, point of no turning back, gates are openResting- back to around -70** start to blend together- the refractory region becomes the action and then the resting regionmoves up neurons can send more than one impulse but can never send them all at once ( why it is so important that repolarization is fast, so that you can have another AP as soon as


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