Lecture4 transmission


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Lecture4 transmission

  1. 1. Neurons – Electrochemical Communication
  2. 2. Preview of today’s lecture Electrochemical Communications  communication between neurons  Neurotransmitters  movie
  3. 3. Structure of a synapse presynaptic membrane postsynaptic membrane synaptic cleft
  4. 4. Structure of a synapse synaptic vesicles are produced by Golgi apparatus in the soma ORby recycled matter in the cisternae of the terminal button: Pinocytosis
  5. 5. Neurons – from electrical to chemical• vesicles release neurotransmitters acrossthe synaptic cleft• the released neurotransmitter leads to post-synaptic potentials (hyperpolarization ordepolarization) that alter the firing rate of thereceiving neuron (decrease or increase) • axon terminal contains synaptic vesicles
  6. 6. Structure of the synapse• as viewed under an electron microscope
  7. 7. Structure of the synapse• synaptic vesicles fusing with the presynaptic membrane
  8. 8. Structure of the synapse• synaptic vesicles fusing with the presynaptic membrane
  9. 9. Neurochemicals• Neurotransmitters - chemical substance released from the end of a neuron during the propagation of a nerve impulse; it relays information from one neuron to another.• Neuromodulators – secreted in larger amounts and diffuse further (composed of peptides)• Hormones – produced in endocrine glands – released into extracellular fluid to be taken up by specific target cells
  10. 10. Binding• only specific neurotransmitters will bind with specific receptor sites – like a key in a lock• chemical that attaches to a binding site is a ligand• neurotransmitters are naturally produced ligands• neurotoxins are also ligands and various drugs have their effect in the same manner – artificially produced ligands (e.g., LSD)
  11. 11. Neurons – from electrical to chemical Only specific neurotransmitters will bind with the post-synaptic membrane.
  12. 12. Binding sitesAxodendritic – synapse on the dendrite of the neuronAxosomatic – synapse on the somaAxoaxonic – synapse on the axon Axodendritic Axosomatic Axoaxonic
  13. 13. Receptors• neurotransmitter specific postsynaptic receptors• open to allow ions to flow into the postsynaptic neuron• two main types • ionotropic • metabotropic
  14. 14. Ionotropic receptors• receptor site has its own ion channel• contain sodium channels• fast acting and short lasting
  15. 15. Metabotropic receptors• indirect method• located nearby G-proteins• G-proteins in turn activate an ion channel• slower to begin and longer lasting
  16. 16. Metabotropic receptors• G-proteins can also activate second messengers – enzymes that in turn activate an ion channel
  17. 17. Excitatory or inhibitory post-synaptic potentials.• once neurotransmitters are bound to the post synaptic membrane theelectrical charge is now altered in the receiving neuron • the change in the electric charge can be more positive than the resting potential (excitatory) or more Inhibitory negative than the resting potential (inhibitory)
  18. 18. Excitatory or inhibitory post-synaptic potentials.
  19. 19. Post-synaptic potentials• determined by the ion channel opened by the neurotransmitter and not the transmitter itself• graded – the potential dissipates with distance traveled• smaller in magnitude than action potentials• action potentials are always excitatory – post-synaptic potentials can be either excitatory or inhibitory
  20. 20. Post-synaptic potentials• excitatory PSP – typically related to sodium ion channels (rush of Na+ into the cell makes it more positively charged)• inhibitory PSP typically related to potassium ion channels (extra K+ maintained inside cell by sodium-potassium pump leaks out making the cell more negatively charged)• action of Cl– channels depends on the state of the receiving neuron – if depolarised Cl– will bring the cell back to a resting state
  21. 21. Terminating the PSP• reuptake – rapid removal of neurotransmitter from the synaptic cleft• SSRIs (selective seratonin reuptake inhibitors – e.g, Prozac) prolong the PSP by inhibiting reuptake
  22. 22. Summation of post-synaptic potentials.• whether the PSP leads to the excitation or inhibition of the neuron depends on the combined effects of many PSPs
  23. 23. Neural integrationSpatial integration: equal excitatory and inhibitory input will cause nochange
  24. 24. Neural integrationTemporal integration: ripples can combine to make bigger ripples
  25. 25. Autoreceptors• autoreceptors respond to neurotransmitters they produce• regulate synthesis and release of other transmitters• metabotropic• usually inhibitory – may control amount of neurotransmitter released
  26. 26. Other types of synapses• axoaxonic – modulate the neurotransmitters in the presynaptic neuron• gap junctions – electrical synapses – the synaptic cleft is much smaller – ions pass directly from one neuron to another
  27. 27. Why do you need to know all this?• different disease processes involve different aspects of the basic electrochemical transmission of neural information• Parkinson’s Disease – dopamine deficiency• Multiple Sclerosis – affects the myelin sheath of white matter• Epilepsy – abnormal electrical stimulation• Alzheimer’s Disease – neurofibrillary tangles may affect the transport of neurotransmitters
  28. 28. Review Questions1 ) NeuromodulatorsA) are rarely of a peptide form.B) are secreted from a neuron and only effect an adjacent neuron.C) are inevitably inhibitory.D) are secreted from neurons, but dispersed widely in the brain.E) are typically secreted in very small amounts compared to neurotransmitters.2 ) Most ________ are secreted into the extracellular fluid from endocrine glands or tissues.A) neurotransmittersB) neuropeptidesC) modulatorsD) hormonesE) Pheromones3 ) Large synaptic vesicles are produced in theA) soma.B) dendrites.C) terminal buttons.D) dendritic spines.E) neuroglia.
  29. 29. Review Questions4 ) Which of the following is true of neurotransmitter function?A) Neurotransmitters diffuse widely in the brain to exert changes in metabolism.B) Neurotransmitters directly alter ion channels using a second-messenger chemical.C) Neurotransmitters are released into the synapse from the cistaerna.D) Neurotransmitters open ion channels in the postsynaptic membrane.E) Neurotransmitters alter ion channel activity for minutes.5 ) Which of the following will produce an EPSP?A) opening a sodium channelB) closing a sodium channelC) opening a potassium channelD) opening a manganese channelE) closing a calcium channelNice review animation
  30. 30.  For Next TimeStart reading Chapter 3  Structure of the Nervous System
  31. 31.  Movie  Behaving Brain