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University of Toronto Mississauga
James Fullard

Introduction to course and bioelectricity Membrane channel - extremely specific; passive vs active; allows cells to change its internal condition Neuron membrane- pull out patches to see how it works Neurons work as a network; allows quick communication across the body, developed because our size increased so need quick communication 2 ways of communication: 1.) Molecules -> hormones (expensive) 2.) Bioelectricity (inexpensive, fast, short-term); created by channels System of nerve cells developed before humans so we can use models (squids, earthworm) because they are simple system (not as many nerve cells) Electrical model of cell membrane Membranes possess a Potential (V)->imbalance of charges; Membrane potential intracellular potential is ve relative to extracellular; Membrane : keeps outside + inside electrically different (+/-) Potential (V) can result in current (I) ->Vmemb =have potential that results in movement of charged particles (current); given a chance, charges will move to correct imbalance so +ve from outside move inside cell; once charges start to move, have current Current encounters resistance (R )->as +ve charges move inside cell, it encounters R -> electricity does not slow down when it encounters R. Electricity always constant speed so can only be hindered or reduced by resistance; R changes the amount of electricity passing through (like a doorway) Resisted current creates new potential-> molecules pile up due to high resistance; so few can get through so develops a new potential) Biological systems use potentials as triggers ex. channels, muscle contraction So electricity -> causes potential -> causes trigger Vmemb-> membrane voltage change (changes potential) Ohms Law: E= IR Amount of potential is determined by the current multiplied by the resistance it encounters 1. Potential (E) an imbalance in charge (V, Volts, millivolts, mV) biological sys: use mV 2. Current (I) the movement of charge (A, Amperes; microamperes, A) bio sys: use A 3. Resistance (R) the opposition to current (, Ohms, megohms, M) bio sys: use M 4. Capacitance (C) the storage of charge (F, farads, picofarads, pF) bio sys: use pF The fundamentals of DC (direct current) electricity Concepts in DC electricity. Electron versus ion (bio) electricity. Computing and measuring potential, the digital oscilloscope. Lipid Core (bilipid layer)- capacitance- filled with fat; very unconductive so need... Membrane channels (ion channels) provides conductance: it opens and closes and allows movement of charge; not great conductor because also provides huge resistance its a tiny hole - Its a biological event so need potential (E) Therefore, the membrane channel is the sourse of conductive pathway (small door) but also source of resistance (during rush hour, its hard to get though) Have choice of where current goes: through channel (I ) oR through bilipid layer (I ) c How to compute the values for secondary potentials : use Ohms Law E = I R (potential equals current times resistance) I = E R (current equals potential divided by resistance) 1 determine Total current: I = E R I = 1.5 11= 0.1363A (same throughout circuit) Secondary potential the result of current encountering new resistances (as current encounters nd 0 0 2 resistor, 2 current gets smaller; have 2 potential originating here; the 2 resistors (in line with each other) develop separate potentials Resistances in series: add their resistances The bigger the resistance, the bigger the potential The sum of all secondary potentials (E totalSource potential Resistances in series increases total resistance -> 1 path Resistances in parallel decrease total resistance -> path of least resistance will be dictator
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