42519 21 Voltage gated channel Openclose when local charge voltage changes

42519 21 voltage gated channel openclose when local

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4/25/19 21 Voltage gated channel Open/close when local charge (voltage) changes Located on excitable membranes Neuron axons Types – Na – K – Ca "Lehninger: Principles of Biochem istry – 4th edition" by Nelson and Cox FYI
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4/25/19 22 Consider the pics: where red indicates a depolarization occurring
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4/25/19 23 On excitable membranes… voltage gated channels open in response to ions moving Voltage gated Na channel Voltage gated K channel Action potential initiation
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4/25/19 24 Action potentials Why do VG sodium channels open? threshold voltage all or none propagated initiated at initial segment travel down axolemma Graphing the changes in the membrane voltage…
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4/25/19 25 Action Potentials refractory periods Absolute Relative absolute refractory period Tim e of depolarization and sodium channel inactivation relative refractory period Stronger than norm al stim ulus is required to generate an action potential Propagation of AP ± s Continuous Saltatory
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4/25/19 26 FYI Axon types: diameter, propagation speed, and information Type A fibers Large, myelinated, fast 268 mph Type B fibers Medium, myelinated 40 mph Type C fibers Small, unmyelinated 2 mph Type A Position, balance, delicate touch, somatic motor commands Type B & C Temperature, pain, touch, Visceral motor commands Synapse: where two neurons communicate Presynaptic cells Postsynaptic cells
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4/25/19 27 Synapse Anatomy Presynaptic neuron Synaptic vesicles – Neurotransmitter Postsynaptic cells Have receptors Chem ically gated channels – Neurons Muscle fibers Gland cells Synaptic knob: Reabsorption and reassembly of neurotransmitter breakdown products Synapse types Electrical – ions Chemical – neurotransmitters
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4/25/19 28 uncommon gap junctions – connexons A few locations in CNS & PNS vestibular nuclei – eye – ciliary ganglia AP ± s always elicit AP ± s FYI Electrical synapses Chemical synapse Presynaptic neurons store neurotransmitter in synaptic vesicles release neurotransmitters in response to action potentials Neurotransmitter types Excitatory neurotransmitters: depolarizing effect Inhibitory neurotransmitters: hyperpolarizing effect Synaptic cleft Enzymes inactivate neurotransmitters Postsynaptic neuron
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4/25/19 29 Cholinergic synapse Example of a chemical synapse AP arrives at terminal Voltage gated Ca channels open…Ca ions diffuse in – Why? Synaptic vesicles move neurotransmitter is released Acetylcholine (Ach) Calcium Homeostasis from Ch 6 ECF [Ca ++ ] ranges 4.3 – 5.3 mEq/L; blood 8.5 – 11.0 mEq/L ICF [Ca ++ ] – 2x10 -7 mEq/L or 0.0000002 mEq/L
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4/25/19 30 Cholinergic synapse Ach opens chemically- gated Na channels Post-synaptic membrane permeability changes – Na ions enter causing a ________________ Enzymes inactivate neurotransmitters – acetylcholinesterase inactivates Ach Cholinergic synapse summary Question time
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4/25/19 31 many other neurotransmitters exist Norepinephrine (NE) Usually excitatory FYI Dopamine
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  • Spring '18
  • Mark Bolke

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