2 Electrotonic Properties

2 Electrotonic Properties - b c = 2π1 ~6.28 c c = 2π2...

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Electrotonic Properties Reading: Squire ch 5 Coloring: 2-1, 4, 7, & 8
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Basic neuronal functions 1. Intrinsic activity 2. Receive input from other cells (pre-synaptic neurons) 3. Integrate multiple inputs and intrinsic activity 4. Encode output response 5. Send final signal onto other cells (post-synaptic neurons)
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Compartmental Models r i = internal resistance r m = membrane resistance capacitance resting potential
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Space constant & resistance λ = √(r m /r i ) V/V 0 = 0.37 at the point where x = λ X= distance along axon V 0 V = electrotonic potential Therefore and increase in specific membrane resistance (R m ) will result in an increase r m for a given segment, an increase in λ, and a greater spread of electrontonic potential. r m = R m / c c = 2πr r=2μm r=2μm r=2μm
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Space constant & axon diameter r m = R m / c c = 2πr Spread of electrotonic potential also relates to the diameter of the cable. To double the spread of current, the λ = √(r m /r i ) X= distance along axon a) c = 2π.5 ~3.14 b) c = 2π1 ~6.28
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Unformatted text preview: b) c = 2π1 ~6.28 c) c = 2π2 ~12.56 r m = 1 / 3.14 = .31 R m = 1 r m = 1 / 6.28 = .16 r m = 1 /12.56 = .08 Myelin sheaths surrounding the axon allow for electrotonic potentials to spread faster and farther than would be possible in an unmyelinated axon Inter-myelin spaces (nodes) are densely populated with voltage sensitive Na+ channels The reduced diameter of dendrites relative to parent branches leads to impedance mismatches. Large diameter = low resistance Small diameter = large resistance a= two small branches = fast decay c= larger branches = slower decay Current injected here Soma out to dendrites Dendrites in to soma http://www.uky.edu/~othibau/ Cable properties also apply to dendritic spines Extremely small volumes require small number of ions to induce a potential Calcium imaging is one tool used to interpret neuronal activation and to monitor electrotonic potentials...
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