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UMass Amherst BIOLOGY 152 - Nervous System

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BIOLOGY 152 1st Edition Lecture 15Outline of Last Lecturea. Gas Exchange Continued b. Circulation i. 3 Systems forVertebrates II. The Nervous System Outline of Current Lecturea. Neuron Morphology b. Resting Membrane Potential Current LectureNeuron MorphologyMembrane potential leading into the action potential of neurons• Dendrites — where the signal comes in from another neuron • Cell body — Where the nucleus is, mitochondria are, where protein translationhappens and transcription happens, also part of apparatus that unifies thesignals coming in from all the different dendrites (“integrates” incoming signals)• axon hillock — determines whether the axon is going to fire or not • axon — long process that goes from the cell body to the synapse where it interfaces with another neuron (dendrites), synapse is where signal goes from electrical signal in the axon, to the chemical signal that will cross the synaptic cleft • postsynaptic cell and presynaptic cell (relative to what synapse you’re referringto) • synaptic cleft — where neurotransmitters cross • some that are electrical to electrical (have gaps between 2 axons, there is nogain there so you lose signal) but it is very fast so some responses useelectrical • ex: squirting ink response in squid usually electrical • neurotransmitters — give you gain in signal, when you switch from electrical tochemical it will boost your signal, and it also allows you to have multiple signals• Myelin sheath/myelination — vertebrate neurons are myelinated, meaning that a specific kind of lipid-rich membrane wraps around the axons in the central nervous system (schwann cell makes the membrane, this cell is wrapped around)• there are spaces where there is no sheath = nodes of rainier • this insulates the axons, helps with longer transmission and less drop of signal (increase transfer sheath, if you lose myelin you can get cross-talk between neurons, which is bad) • invertebrates don’t have this, so they have axons with a much larger diameter For the following questions see slide 5**Clicker Questions**Axon Hillock is what in picture? DWhere signal “enters” a neuron? AWhich combination of axon features would lead an axon to communicate with downstream cells most slowly?wider is better if its un myelinated — the reason the squids have the very wide ones are to help with the transfer (increase conductivity)un myelinated, thin and longResting Membrane PotentialIf you take a chamber & separate it with a semi-permeable membrane (permeable to potassium and not chloride for example) and you have KCl on both sides- gold = Cl - blue = K what will happen over time is that the blue ions (K) will move to even out the concentration (only K moving not Cl because membrane is selectively permeable)as you move you develop charge separation — you’re getting a net negative charge build up on the left side of the membraneso because of concentration gradient, K is moving across to the right, but because only K can move you get a charge imbalance causing the left side to be 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.more negative- charge separation has a potential that can be harnessed to do work (voltage) ormembrane potential, which can be measured - can use the Nernst Equation to understand how this membrane potential works- tells you what voltage will hold a particular concentration gradient for one ion - at 37 degrees it reduces to the concentration outside and the concentrationoutside - E = 62mV(log concentration of outside/concentration of inside) seeformula in slides on pg 12 can stick a reference electrode into the cell and measure the voltage (this is how tomeasure the change in membrane potential)CQ: 100 mM K inside and 5mM K outsideAnswer = A (-80)- E = 62mV(log5/100) - = 61mV(-1.3) = -80 - negative because when K moves, you get a negative membrane potential inside(measuring outside to in, and so since potassium wants to move in, you get anegative potential) Same concentration as before (-80) but external K raised 4 times, what should happen to the voltage?- you’re lowering the concentration gradient (smaller) therefore the voltagewill be less because you don’t need as much voltage to hold thatconcentration gradient - answer = it will be more positive - as long as conc. outside increases with respect to inside concentration,membrane potential because less negative What mechanism could be responsible for the high permeability of cell membranes to potassium?- there are protein channels specific for potassium in the membrane thatallows for K to cross - have K on intracellular side, and you have membrane channels that allow K todiffuse but not other things so even though there is sodium outside, they don’tdiffuse readily across the membrane - so potassium has dramatic effect of membrane potential of almost all cells In the simulation: sodium potential for a positive ion (high on outside low on inside) and positive potentialchloride is a negative ion, so even though it is also high on the outside and low on the inside, it has a negative membrane potential- controlled almost entirely (most of the time) by potassium - K has high permeability, Na and Cl have low, so potassium is determining thepermeability of the membrane - E is the voltage, stands for electromolar force **Clicker Question**What would happen to the membrane potential if I increase the Na permeability as high as it could be, what should happen to the membrane potential?• it would become more positive, because the sodium is much higher on the outside than it is on the inside, and if you increase it’s permeability it rushes inside into it’s cell (in initial chloride is rushing out) so if the positive is going in, it makes the inside positive. • why doesn’t it go any higher than 58.7? why not become more positive? Becauseit came to equilibrium, it reached a particular value - blue line shows Nernst potential for sodium,the potassium gives you the lowestyou can get so it must be between the two If you increase the permeability of the membrane for chloride, what would happen to the membrane potential?• Nernst


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