Synapse and Neurotransmitter

1. Synapse and Neurotransmitter 苏 擘 神经生物学研究所（6号楼6620） bxs103@sdu.edu.cn 0531-88382329

3. Synapse and Synaptic Transmission

4. Neurons Structure & Function Introduction • Cell Body (Soma):Life Support • Protein Synthesis • Single Nucleus • Axon: Longest process transmits messages away from cell body • Dendrites: Multiple processes off cell body – receive messages

5. Neurons

8. Axons Dendrites Take information away from the cell body Take information to the cell body Smooth surface Rough surface (dendritic spines) Generally only 1 axon per cell Usually many dendrites per cell No ribosome Have ribosomes Can have myelin No myelin insulation Branch further from the cell body Branch near the cell body Differences between Axons and Dendrites

10. Important Features of Neurons EXCITABLE Membrane: Able to regulate the movement of ions (charges) across and along membrane---SIGNAL TRANSDUCTION

12. Action Potential

13. Outline • Types of synapses • Signal transmission at chemical synapses • Principles of synaptic integration

14. Synapse: a specialized junction that transfers nerve impulse information between neurons or neuron and effector cells.

15. Types of Synapses • Electrical synapses • Occur at specialized sites called gap junction • Common in non-neural cells (astrocytes) and early embryonic stages • Chemical synapses • Predominates in the mature human nervous system

16. Axodendritic synapse Axosomatic synanpse Axoaxonic synapse

17. Gray’sType I Gray’s Type II

18. ElectricalSynapse • Gap junction • Adjacent cells electrically coupled through a channel. • Ionic current • Cytoplasm continuous • No synaptic cleft - 3.5nm • Brief delay • Bidirectional

19. Rapid Transmission of Signal at Electrical Synapses An action potential in thepresynapticneuron causes the postsynaptic neuronto be depolarized within a fraction of amillisecond.

20. Gap junctions • Channels: • Connexon • Diameter is 2nm • 6 subunits: connexin

21. The chemical synapse is a specialized junction that transfers nerve impulse information from a presynaptic membrane to a postsynaptic membrane using neurotransmitters. Axodendritic synapse Axosomatic synanpse Axoaxonic synapse

22. Chemical Synapses • Presynaptic element • Synaptic vesicles • Active zone • Synaptic cleft • Postsynaptic density

23. Neurotranmitters 20-50nm cleft Syanptic delay: 1-5ms or longer unidirectional Chemical Synapses

24. Chemical synapses as seen with electron microscope

25. 电镜冰冻蚀刻技术显示突触结构

26. Distinguishing Properties of Electrical and Chemical Synapses

27. Outline • Types of synapses • Signal transmission at chemical synapses • Principles of synaptic integration

28. Signal transmission at chemical synapses From a presynaptic membrane to a postsynaptic membrane using neurotransmitters

29. Signal Transmission at Chemical Synapses • Neurotransmitters • NT Receptors • EPSP and IPSP

30. Neurotransmitters • Precursor transport • Synthesis • Storage • Release • Activation • Termination diffusion, degradation, uptake, autoreceptors

31. Postsynaptic Membrane Presynaptic Axon Terminal Terminal Button Dendritic Spine

32. (1) Precursor Transport

33. _ _ _ NT (2) Synthesis enzymes/cofactors

34. (3) Storage in vesicles

35. NT Vesicles Terminal Button Dendritic Spine Synapse

36. (4) Release Terminal Button Dendritic Spine Synapse Receptors

37. Terminal Button Dendritic Spine AP Synapse

38. Exocytosis Ca2+

39. Release • Quanta release • Each vesicle contains one quanta of neurotransmitter (approximately 7000 molecules)

40. (5) Activation

41. (6) Termination

42. (6.1) Termination by... Diffusion

43. (6.2) Termination by... Enzymatic degradation

44. (6.3) Termination by... Reuptake

45. (6.4) Termination by... Autoreceptors A

46. Synthesis and Storage • A: peptide • B: amine and amino acid

47. A model for Ca2+-triggered vesicle fusion

48. Ca2+ CAM CAMKII

49. A electron microscopy view of NT release

50. Fine structure of vesicle fusion sites