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Unformatted text preview: 2/9/11 1 Physiology lecture 8 : Sensory system Synapses (chapter 6) The sensory system (chapter 7) For next time : please read chapter 8 Tetrodotoxin is a potent neurotoxin with no known antidote, which blocks action potentials in nerves by binding to the pores of the voltage- gated, fast sodium channels in nerve cell membranes. puffer Fsh Blow fsh Sushi to die or Junctional regions between neurons, or between a neuron and another cell, where inormation is passed rapidly rom one cell to another Synapses: The synapse is the point of communication between two neurons that operate sequentially. A chemical synapse 6 A neuron that is postsynaptic to one cell can be presynaptic to another cell. Pre- and post-synaptic 2/9/11 2 Neurotransmitter release Acetylcholine bound to receptor site opens ligand-gated Na + channel 1. Action potentials arriving at the presynaptic terminal cause voltage- gated Ca 2+ channels to open. 2. Ca 2+ diffuse into the cell and cause synaptic vesicles to release acetylcholine, a neurotransmitter molecule. 3. Acetylcholine diffuses from the presynaptic terminal across the synaptic cleft. 4. Acetylcholine molecules combine with their receptor sites and cause ligand- gated Na + channels to open. Na + diffuse into the cell and causes depolarization. If depolarization reaches threshold, an action potential is produced in the postsynaptic cell. Ca 2+ Voltage-gated Ca 2+ channel Synaptic vesicle Postsynaptic membrane Acetylcholine 4 Synaptic cleft Action potential Presynaptic terminal Na + 1 2 3 4 An example: The cholinergic synapse When synaptic transmission is blocked (convulsions, respiratory paralysis, and death within several minutes.) In cosmetics: In chemical warfare: Blocking of ACh release - botox Blocking of Ach hydrolysis - nerve gas An Excitatory Post-Synaptic Potential (EPSP) is a graded depolarization that moves the membrane potential closer to the threshold for firing an action potential (excitement). EPSP An inhibitory postsynaptic potential (IPSP) is a graded hyperpolarization that moves the membrane potential further from the threshold for firing an action potential (inhibition)....
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