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Final exam review 13 pages of notes of the key points of the procedures and results and summaries of the introductions

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Bruce Wolff

Lab #1: Generation of Electrical Potentials by an Artifical Membrane Hans Ussing chamber permeable to cations like Na+ and K+ but not anions like Cl- and I- V=0.199*T*log(a1/a2) activity coefficient: measure of how independently ions behave when dissolved; small at low concentrations, high at high concentrations activity=conc.*activity coefficient Procedure 1. make 0.1M, 0.01M, 0.001M, 0.002M KCl 2. add 60mL of each solution being compared; fill in Ussing chamber at same time so pressure is equal; allow air bubbles to flow in at a rate of 5-10 bubbles per second 3. insert black electrode into subchamber #1; set to 200mV; turn multimeter off after each reading Results Concentration of KCl Trial 1 2 3 4 5 6 7 Subchamber 1*10 1*10^-3 2*10^-3 1 1 1 1 1: ^-3 Subchamber 0.01 0.1 1 2*10^-3 0.01 0.1 1 2: Concentrati 10 100 500 500 100 10 1 on Factor Potential -28.4 -86.1 -101.5 102.8 85.3 42.1 -0.1 Reading #1 (mV) Potential -28.1 -84.2 -90.1 102.6 84.3 43.6 -0.5 Reading #2 (mV) Potential -28 -85.3 -88 101.3 84 43.3 -0.2 Reading #3 (mV) Average -28.2 -85.2 -93.2 102.2 84.5 43 -0.3 Potential Reading (mV) Corrected -27.9 -84.9 -92.9 102.5 84.8 43.3 0 average potential reading (mV) Calculated -56.6 -110.9 -146.4 146.4 106.8 52.4 0 Potential (mV) Trial 1 V = 0.199 x 293K x log[(0.001 x 0.965)/(0.010 x 0.902)] V= 0.199 x 293 x -0.971 V= -56.6 mV Therefore the calculated potential for trial 1 is -56.6mV. Study Questions 1. A selectively permeable membrane forces the concentration gradient unable to go from high to low. This causes a difference in charge, similar to the resting membrane potential of a cell. 2. The membrane in this experiment does not have ion channels and K+ and Na+ have the same permeability, so it cannot alter the resting membrane potential and is determined solely by the difference of the concentrations of solutes. 3. They do have the same membrane potential size because it is an artificial membrane and there are no ion channels to modify the concentrations so its membrane potential depends only on the beginning concentration difference. 4. K+ passes more easily through the membrane than Na+. If K+ didn't pass very easily through the membrane, the RMP would be closer to -30mV (+60mV for Na+, -90mV for K+) but might be offset a little if Na+/K+ ATPase was pumping out 3 Na+ for every 2K+ in. 5. The activity coefficient is how independently solutes behave in a solution. At higher concentrations there are more intermolecular forces interfering, so the activity coefficient is lower; at low concentrations ions act more independently so the activity coefficient is higher. 6. The purpose of bubbling is to ensure a good mixing motion within solutions and prevent unstirred layers of solution next to the membrane, possibly altering the RMP. Lab #2: Non-invasive Recording of Action Potentials From a Small Annelid Worm When myelin is unavailable, large-diameter axons are more effective because it can transmit electrical signals faster. The blackworm Lumbriculus variegatus has axons up to 20micrometers in diamater to respond quickly to stimuli. Sensors in the anterior end of the body respond to dangers signals by generating AP carried by the medial giant fibre to the muscles of the body wall causing the head to reflexively withdraw. The second pathway involves a pair of lateral giant fibres that conduct signals that originate in sensory cells in the posterior and mediate a tail-withdrawal reflex. They act as a single axon since they are joined by lateral extensions. The oscilloscope records the difference in electrical potential between two points on the worms surface which results in a biphasic action potential.Faraday cage reduces interference in the circuitry that may be caused by external fields Procedure 1. set to potential difference of 5mV, sweep speed at 2.5ms 2. head of the worm is more darkly pigmented and mobile 3. stimulate the worm lightly with the widget 4. spike on the oscilloscope tracing should have the same polarity in both tracings conduction velocity V = d -2 /1 -2 1 d=distance between 2 pairs of electrodes= 10mm t=time from arrival of AP at first pair until arrival at next pair Study Questions 1. It reduces the ions leakage (which decreases strength of AP) and reduces resistance (can travel faster). Myelinated can be around 10micrometers, while unmyelinated would need to be about 500micrometer. 2. The refractory period prevents the A
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