بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

2. Physiology of CNS SYNAPSE By Dr. Abdel Aziz M. Hussein Assist. Prof. of Physiology Member of American Society of Physiology

3. Synapse Def: • Functionalconnection between 2 neurons • Or Areas of contact between neurons in the C.N.S.

4. Synapse 2)Types of Synapses:

5. Synapse

6. Electrical Synapse

7. Electrical Synapse

8. Chemical Synapses Physiological anatomy:

9. Chemical Synapses

10. Chemical Synapses Types:

11. Chemical Synapses

12. Synaptic Transmission

13. Mechanism of Synaptic Transmission • It involves 3 steps:

14. 1.Release of Neurotransmitters

16. 1.Release of Neurotransmitter • It involves the following steps: • During rest, both the pre. and postsynaptic membrane have R.M.P is about -70 mV. • Stim. of presynaptic neuron → generation of AP → AP reaches the synaptic knob→ transient opening of the VGCa2+ channels Ca2+ influx → Ca2+ causes the vesicles to fuse with the knob membrane at active zones vesicles release the transmitter by exocytosis in cleft

17. 1.Release of Neurotransmitter • The number of vesicles ruptured depends upon the concentration of Ca2+ within the active zone of the knob. • The empty vesicles then separated from the knob membrane and mobilized back and fuse with the smooth E.R.

19. 2. Actions of Neurotransmitters

20. 2. Action of Neurotransmitter on Postsynaptic Neuron • Post-synaptic receptors are 2 types;

21. Postsynaptic Receptors

22. Ligand-gated Ion Channels

23. Cation Ion Channels + + - - + + + - - + + _ ____ _ ____ + + + + + Biophysics , Abdelaziz Hussein

24. Cation Ion Channels

25. Anion Ion Channels + + - - - - + - - - - + + - - - Biophysics , Abdelaziz Hussein

26. Anion Ion Channels

27. G-protein Coupled Postsynaptic Receptors

28. G-protein Coupled Postsynaptic Receptors • Binding of transmitter to its receptor→ G- protein is activated (by replacement of its GDP with GTP) → separates the α component from the G-protein. • The separated active α component can perform; • Opening specific ion channelse.g. 2nd- messenger gated K channels • Activation of particular enzymes→ catalyze the formation of the 2nd messengers, such as cyclic AMP, cyclic GMP, IP3,diacylglycerol (DAG) • Regulation of gene transcription→ control synthesis and production of certain proteins within the neuron

30. Postsynaptic Potentials

31. Postsynaptic Potentials • Postsynaptic potentials (PSPs) are 2 major types: • EPSPs • IPSPs

32. Excitatory Postsynaptic Potentials (EPSPs) 1)Def. • It is a state of partial depolarization which occurs in the postsynaptic membrane due to single presynaptic impulse

33. Excitatory Postsynaptic Potentials (EPSPs) 2)Mechanism: • When the excitatory chemical transmitter bind to and open ligand-gated cation channels→ allow much Na influx than K efflux→ depolarization of postsynaptic membrane → brought the postsynaptic membrane potential close to the threshold for excitation → called EPSP.

35. Excitatory Postsynaptic Potentials (EPSPs) 3) Characters or properties : • Partial depolarization not reach firing level • Increases the excitability as it carries the membrane potential to FL • Localized i.e. not spread. • Short duration i.e. decays within 15 m.sec. • Its amplitude (very small) about 0.5 mv • To produce action potential must be summated. • The summation is of 2 types: spatial and temporal summation

37. Excitatory Postsynaptic Potentials (EPSPs) Summation : • A depolarization of at least 10 to 20 mV is required to reach the usual threshold, so EPSPs must be summated a) Spatial: • By stimulation of several presynaptic fibers that converge on the post synaptic neuron at the same time. b) Temporal: • By stimulation of a single presynaptic neuron repetitively (successively) within very short duration (less than 15 m.sec).

39. Excitatory Postsynaptic Potentials (EPSPs) • When the summated EPSPs reach the firing level, This will generate an action potential at the initial segment of the axon (axon hillock).

40. Miniature EPSPs • During rest: some Ca2+ enters the synaptic knob  release of few vesicles of neurotransmitter → weak depolarization of postsynaptic membrane → miniature EPSP

41. Inhibitory Postsynaptic Potentials (IPSPs) 1)Def. • It is a state of partial hyperpolarization which occurs in the postsynaptic membrane due to single presynaptic impulse

42. Inhibitory Postsynaptic Potentials (IPSPs) 2)Mechanism: • When the inhibitory chemical transmitter bind to and open ligand-gated anion channels→ allow much Cl influx → hyperpolarization of postsynaptic membrane → brought the postsynaptic membrane potential away from the threshold for excitation → called IPSP.

44. Inhibitory Postsynaptic Potentials (IPSPs) 3) Characters or properties : • Partial hyperpolarization not reach firing level • Decreases the excitability as it carries the membrane potential to FL • Localized i.e. not spread. • Short duration i.e. decays within 15 m.sec. • Its amplitude (very small) about 0.5 mv • To produce action potential must be summated. • The summation is of 2 types: spatial and temporal summation

46. Miniature IPSPs • During rest: some Ca2+ enters the synaptic knob  release of few vesicles of neurotransmitter → weak hyperpolarization of postsynaptic membrane → miniature IPSP

47. IPSPs and EPSPs • A Postsynaptic neuron may receive many presynaptic terminals from several hundreds of neurons, some of these terminals are excitatory and the others are inhibitory. • So, both EPSP & IPSP are produced and the effect on the postsynaptic membrane depends upon the net ability of summated postsynaptic potential to drive the membrane either towards or away from threshold level

48. Interaction of EPSPs and IPSPs

50. 3. Termination of Synaptic Transmission