Chapter 8 Neurons, Part 2

Chapter 8 Neurons, Part 2 - Chapter 8 Neurons Part 2 Four...

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Four Basic Components of Signal Four Basic Components of Signal Movement Through Neuron Movement Through Neuron 1. Input signal (graded potential) 2. Integration of input signal at trigger zone 3. Conduction signal to distal part of neuron (= Action Potential) 4. Output signal (usually neurotransmitter) Chapter 8: Neurons, Part 2
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Review of Solute Distribution Review of Solute Distribution in Body Fluids in Body Fluids The [ ] gradient of K + is the main source of the membrane potential Change in permeability ot Na + can allow influx of Na + Depolarization •Electric signal created Controlled by gated channels
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Graded Potentials Graded Potentials Fig 8-7 Trigger Zone Usually Axon Hillock and/or Initial segment of axon •Many Na + Channels Some stimuli may be inhibitory Hyperpolarizing effect
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Graded Potentials Graded Potentials Location: Any receptor Strength (= amplitude) ~ strength of triggering event Travel over short distances to trigger zone Amount of local current flow is variable Diminish in strength as they travel May be depolarizing (EPSP) or hyperpolarizing (IPSP) Fig 8-7
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AP Subthreshold potential vs. Suprathreshold Subthreshold potential vs. Suprathreshold potential potential Fig 8-8 Graded potential starts here
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Location ? Travel over long distances Do not lose strength as they travel Are all identical (all-or-none principle): 100mV amplitude Represent movement of Na + and K + across membrane Conduction Signals: Action Potentials (AP) Action Potentials (AP) Ability to propagate the AP = Excitability
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Ion Movement across Cell Membrane Ion Movement across Cell Membrane During AP During AP Sudden increase in Na + permeability Na + enters cell down electrochemical gradient (+ feedback loop for ~ .5 msec) Influx causes depolarization of membrane potential = electrical signal What stops + feedback loop? The Na + inactivation gate closes.
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Na Na + Channels in Axon Have 2 Gates Channels in Axon Have 2 Gates Activation gate and Inactivation gate Na + entry based on pos. feedback loop needs intervention to stop Inactivation gates close in delayed response to depolarization stops escalating pos. feedback loop Fig 8-10
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Model of Activation and Inactivation Gates Model of Activation and Inactivation Gates
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AP-Graph AP-Graph has 3 phases 1. Rising (Na + permeability ) 2. Falling (K + permeability ) 3. “Undershoot” or Hyperpolarization
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Graded potentials A. Produce an effect that increases with distance from the point of stimulation B. Produce an effect that spreads actively across the entire membrane surface C. May involve either depolarization or hyperpolarization D. Are all-or-none E. All of the above
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