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Unformatted text preview: 3/19/2008 1 Nervous system & some sensory (actually very little!) Nervous system & some sensory (actually very little!) Action potential :- Begins in axon hillock, membrane stores charge, like a capacitor- when threshold is reached, fast-acting voltage-gated (cf. ligand-gated before) channels open and Na + rushes inside, discharging the membrane- Influx of Na + causes more voltage-gated channels to Electrochemical activity of neurons Electrochemical activity of neurons Influx of Na causes more voltage gated channels to open, increasing influx of Na + , causing still more channels to open, etc., very quickly all channels are open, via positive feedback loop- At that point, membrane permeability to Na + is 1000x permeability of resting membrane. - It regenerates itself along axon by opening adjacent channels Action potential voltage gated channels : K channel has single slow gate that is closed when resting and opens upon depolarization. Na channel has two gates: fast activation Electrochemical activity of neurons Electrochemical activity of neurons gate is closed when resting, opens in response to depolarization; slow inactivation gate that is open when resting and closes upon depolarization Action potential : All or none response. Amplitude is the same each time, but varies by frequency Refractory areas in front and behind Electrochemical activity of neurons Electrochemical activity of neurons action potential Action potential is ~3 msec, with a 1-2 msec refractory period. Speed of action potential is dependent on diameter of neuron Action potential : Speed of action potential is dependent on diameter of neuron and myelination A) Neuron diameter- Larger diameter conducts faster Electrochemical activity of neurons Electrochemical activity of neurons- resistance to flow of current is lower with larger diameter: depolarization at point can 'reach' further along interior of axon to set up new AP.- A few cm to 100 m/sec in thick giant axons.- Exp/ in crayfish or squid, 1 mm diam. non-myelinated axons facilitate the tail-flip escape response. Action potential : B) myelination- high resistance insulator, no capacitance (ability to store charge)- no charge stored across myelin, and there are almost no channels under myelin Electrochemical activity of neurons Electrochemical activity of neurons almost no channels under myelin.- Na+ channels are highly concentrated at Nodes of Ranvier and the initial segment/hillock Greater- speed in larger-diameter and more heavily- myelinated axons with greater spacing of nodes of Ranvier. - MS, autoimmune disease 3/19/2008 2 Figure 48.11 Saltatory conduction Action potential : Question : how does the CNS distinguish strong stimuli from weaker ones?...
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This note was uploaded on 05/18/2008 for the course BIOL 211B taught by Professor Lowe/zahn during the Spring '08 term at CSU Long Beach.
- Spring '08