Neurophysiology - Study Guide Exam 1
Neurophysiology - Study Guide Exam 1 NSC 4356
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This 5 page Study Guide was uploaded by Christine Thomas on Friday February 5, 2016. The Study Guide belongs to NSC 4356 at University of Texas at Dallas taught by Dr. Dussor in Fall 2015. Since its upload, it has received 164 views. For similar materials see Neurophysiology in Neuroscience at University of Texas at Dallas.
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Date Created: 02/05/16
STUDY GUIDE – NEURO PHYS – EXAM 1 Osmosis Concentration Same on either side of the membrane – isotonic (cell membrane) Concentration is higher on one side of the membrane – hypertonic Concentration lower solute concentration on one side of the membrane – sucks up water – hypotonic – to try to bounce the solute on either side – in the end its going to burst because the cell will swell from pulling in a lot of water Cell membranes Negative charge of the heads of the hydrophilic Hydrophobic – neutral charge Lipophilic – they go right through a membrane Anything with a charge in it cannot get through the membrane Water permeability Anything that ends with “cane” – blocks the channel on the inside – lipophilic drug – it goes right through and is not charged Hydration of Ions Water can take the sodium ion and rap around it – all the neg ions keeps the sodium stable (keeping it happy) Question: which is the mostly likely mechanism by which water crosses lipid membrane – aquaporin's Na/Ca Exchanger Low intracellular calcium levels are maintained by the Na/Ca exchanger What would be a direct effect of the loss of Na/K pump function? – intracellular sodium concentration would increase Assuming the atomic radii are as follows: K>Na<Mg and the electronegativeties are as follows Mg>>Na>>K? – K What inhibits ions from passively diffusing through the lipid bilayer? Hydrophobic tail of the phospholipid Electric Charge and Force Know Coulomb’s Law formula – how the distance the two ion …. Forces Like charges repel each other – related to how far away they are from each other… The closer together then force is going to be higher Further away means it will have a less force Its r squared Two pos charges move 2X as far away from each other as they were in their starting position. The change in electric force on each charge? – 0.25X (fourth) Batteries Separation of charge – device that is capable of moving electric charges V represents battery, R is resister, I is current Redox Reactions Batteries based on redox reactions – chemical reaction results in gaining or loosing of an electron Definitions Current: how many charges are flowing pass in the system in a given period of time Voltage: Resistance – how difficult it is for ions to move from one place to another Conductance – opposite to resistance – how easy it is for ions to move Electricity – flow of ions back and forth Charge – measured in C – there the elementary charge is 1.6 x 10(^-19) C Current - the movement of charge in a given period of time Units of current is A (Amperes – one coulomb of charge in one second of time) Size of a current – what is the difference of electrical potential places How easy is it for it to move from one place to another Electrical potential, conductance, resistance Electrical potential – potential energy per unit of charge Potential difference – what is the difference in electrical potential from one place to another Volts (V) – units of potential difference Conductance – opposite of resistance Depends on what they are moving through Units of conductance – S (siemens) Resistance measured in Ohms Conductance/Resistance QUESTION: The conductance of deionized water (water with no ions) should be – lower than normal water Ohm’s Law I (current)=V (voltage)/R(resistance) V (voltage)=I (current) R (resistance) V=IR If you increase the resistance then there will be few ions which means lower current If resistance goes down, more ions, more current Resistance and Flow Rates Size of needle – the resistance went down So there was less time used You still moved the same amount of liquid and force but the opening was bigger You get a really high flow rate and then it goes away – shorter period of time Even bigger needle – less resistance Question: What did the 10 lb. force represent in the syringe analogy – the voltage Needle is the resistance Analogy Question: Based on our discussion to date what might create the largest force for movement of a charge across a cell membrane? – ion concertation differences Decreasing the resistance of an ion across the membrane by a factor of ten will: - increase the ion’s current by 10 (Ohms law question) Capacitors Devices in electricity that stores charge Two Metal plate with wire attached to each and in btwn the two there is an insulator – cannot flow across …. Must go around … one side can influence the other even though there is no way to flow through … there is an electrical field in the insulated medium… Introduce positive charge on one side which will repel any equivalent pos charge on the other side and rather build neg changes Charge separation It will stay that way unless you give the charges some path so that it can equalize it If you give it a path to flow then you will discharge the capacitor Capacitance= charge (q) / voltage (v) [not as important as the other equation) C (Capacitance) = two consents (area of plates/distance btwn two plates) Capacitors- the cell membrane The cell is a really good capacitor Ions do not go through a layer unless there is ______ Because they are soo close together makes it a good capacitor The cell membrane is a capacitor No charge difference across cause they are equally distributed Over time the charges go to either side to where there is only neg charges on one side and pos on the other side The unit is Farads (f) – units of capacitance of farad 1F will be charged to 1V when 1C of charge is on one conductor All cell membrane - have a capacitance of 1muF/cm square - same thickness cause capacitance is the same in every cell As long as you know that number and the size of that cell then you find the total capacitance QUESTION: if the distance btwn the two layers of phospholipid bilayer were increase, what would happen to the capacitance of the membrane? – decrease (cause you are making the distance bigger and on a fraction the higher the bottom number the smaller the capacitance Resistor in a neuron are ion channels – something ions can clow through which is the ion channel There is a battery in the cell – it is a gradient (sodium gradient) RC Circuit Resistor in a neuron are ion channels – something ions can clow through which is the ion channel There is a battery in the cell – it is a gradient (sodium gradient) Charging a Capacitor There is a limit on how much charge you can introduce onto a plate – this is limited on the strength of the battery you have This is not an instantaneous It rather takes some amount of time to equalize its self Exponential relationship btwn the plates RC Circuit Time on x axis and V on the y axis On the current set up – pos and charges are going to repel pos charge on the other side and the only way they can more is if they go through the resistor and the have to go through it and that resistance is going to influence how fast it you can actually charge the capacitor If it is harder for the ions to go through the resistor and then it will take longer to charge the circuit You would fit a time constant as long as that figure is changing (time constant – how long it takes that thing to change) tou (T thing) = resistance (R) x capacitance (C) Battery out of the game cause there is no path – you have taken the charge the made this path to discharge itself – you are allowing the capacitor to discharge itself through the resistor The time it takes to get through the resistor should be the same as the discharge This is cause you open a part of the circuit Time Constant as a Function of R If you make it double then what it is then it will of course will take longer to do it notice the color lines on the graph… it is take longer to charge We can measure time constant of neurons with electrical measure techniques – measuring how long it takes to get to _______ Time constant how long does it take charge to get to 37% away from its maximum voltage… why 37% away or 63% toward - cause the math behind it has a e in it – basically if you take 1 and divide it by 3 it = 37% Membrane Model Circuit Potassium battery Membrane is the capacitor Parallel Resistance QUESTION: what does ATP do in terms of the circuit model – it keeps the battery charged Resistance of a channel is depended on whether or not the channel is open or closed – not dependent on ATP ATP is pumping sodium in and out – other gradients are dependent on battery – ATP dependent With of bilayer not really changed cause you are just putting insulation on it - not ATP dependent Individual sodium channels has lots of paths to choose from – essentially all are in parallel Membrane Models: Na and K G is the abbreviation of conductance (symbol same as resistance even though they are inverse of each other) Ions are not going to go through directly through the lipid bilayers QUESTION: what do the arrows in the membrane model represent? – change in resistance – depending on whether it is opened or closed cause it can change Membrane is not going to be open or closed – cause it is set so it has no arrow through it QUESTION: why can we treat ionic gradients as batteries in an RC circuit diagram? – Because they create a voltage across the resistor? QUESTION which component in this diagram represents the cell membrane? The capacitor – cell membrane
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