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SIU BIOL 200B - Nervous System

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Biol 200B 1st Edition Lecture 16 Current Lecture OutlineI. OrganizationII. NeuronIII. Nerve ImpulsesIV. Resting Potential V. Action PotentialCurrent LectureNervous SystemOrganization:Sensory receptors – detect stimulusMotor receptors – respond to stimulusNervous system links the two receptors- Neurons and supporting cells1. Sensory neurons2. Motor neurons3. InterneuronsNeuron: nerve cell- Dendrites – input from other neurons- Cell body and axon hillock – signal integration - Axon – signal conduction- Synapse – transmission; where signal is transmitted to other neuronsPresynaptic and postsynaptic cellElectrical signals – only travel I 1 direction (down axon)Nature of Nerve ImpulsesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Electrical potential (voltage) – exists when there is separation of charged particles across some space Ex: batteryResting Potential – Voltage (charge difference) across neuron membrane at resElectrochemical gradient – concentration and charge difference across membrane- Established by Na+/K+ ATPase pump and ion leakingAxon interior is more negatively charged Resting neurons – most permeable to K+As K+ “leaks out” the axon interior is more negatively charged (K+ leak channel)Action Potential: changes in membrane potential are the signals conducted by axonsCentral nervous system sends and receives all information as action potentials4 key points of action potentials:1. Depolarization – ion exchange across membrane, so less polarized2. Threshold potential – action potential will not occur unless depolarization is great enough3. Action potential is all-or-none signal 4. All action potential have the same magnitudeAction Potential occur because voltage-gated ion channels open or close in response to changesin voltageResting potential – voltage-gated Na+ channels closed1. Depolarization – rapid opening of Na+ voltage-gated channel2. Potassium channels open with delayWhich ions drive each part of action potential:- Depolarization – inward flow of Na+- Repolarization – outward flow of K+Na+ channels more likely to open with depolarization (all-or-none)Propagation of action potential down axon1. Na+ enters axon2. Charge spread – depolarization at next ion channel3. Downstream channel opens; Na+ entersSignal amplitude is constantNa+ sodium channels are refractory- Once opened and closed, can’t open for short time- Prevents action potential from propagating backwardsTo make action potential propagate faster:- Increase axon diameter – less resistance to current flow- Prevent Na+ leaking except at discrete sites on


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