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What happens when action potential reaches axon terminal?

What happens when action potential reaches axon terminal? Forms a synapse with another neuron or muscle. Two types: Electrical and Chemical. Chemical Synapse. 1. action potential arrives at terminal 2. voltage-gated Ca channels open 3. Ca triggers exocytosis of vesicles

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What happens when action potential reaches axon terminal?

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  1. What happens when action potential reaches axon terminal? Forms a synapse with another neuron or muscle Two types: Electrical and Chemical

  2. Chemical Synapse

  3. 1. action potential arrives at terminal 2. voltage-gated Ca channels open 3. Ca triggers exocytosis of vesicles 4. neurotransmitter is re- leased, binds to re- ceptor 5. ligand-gated Na or K channels open 6. neurotransmitter broken down, taken up 7. synaptic vesicles re- constituted 8. neurotransmitter stored, awaits next impulse Action potential Synaptic vesicle active uptake Ca2+ voltage- gated Ca channel Ca2+ docking protein K+ Postsynaptic cell Na+

  4. acetylcholine botulinum toxin X X acetylcholinesterase curare (antagonist) nicotine (agonist) Neuromuscular Junction Nicotinic cholinergic synapse

  5. acetylcholine X atropine (antagonist) muscarine (agonist) Muscarinic cholinergic synapse

  6. Post-Synaptic Events Graded vs Action Potentials Excitatory vs. Inhibitory PSPs Pre- vs. Post-Synaptic Inhibition Divergence vs. Convergence

  7. Receptor binding results in opening of agonist-gated K and Cl channels e.g. muscarinic acetylcholine receptor of heart

  8. Receptor binding results in opening of agonist-gated Na channel e.g. nicotinic acetylcholine receptor of neuromuscular junction

  9. One synapse is generally not sufficient to generate a threshold stimulus at the axonal hillock. Most neurons receive thousands of synaptic endings - each of which contributes a postsynaptic potential (EPSP or IPSP) of less than 1 mV. Each of these PSPs are conducted to the axonal hillock with decrement (decay). An action potential will only be generated if the sum of the IPSPs and EPSPs reaching the axonal hillock at any time exceed the threshold voltage.

  10. Dendrite of postsynaptic neuron Axon terminals of presynaptic neuron Dendrite of postsynaptic neuron Glial cell processes Axon

  11. Spatial summation

  12. excitatory inhibitory A D E B C electrode threshold A A+B A+B+C D D+E A+B+C+E

  13. Postsynaptic Inhibition

  14. Presynaptic Inhibition

  15. Divergent circuit Allows for amplification of a signal:

  16. 15-20 internuncial cells in CNS each stimulates several hundred motoneurons each of these stimulates 100-300 muscle fibers single pyramidal cell in the motor cortex of the brain Divergence results in 50,000-fold amplification

  17. Convergent circuit Important for summing, correlating and sorting information in the CNS

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