Learning objectives of Today’s Lecture

1. Learning objectives of Today’s Lecture • Describe the physiological basis of Resting membrane potential of a neuron • Enlist the sequence of events in synaptic transmission • Differentiate between Excitatory Post Synaptic Potential EPSPand Inhibitory Post Synaptic Potential IPSP

2. Synaptic transmission Dr Ghulam Mustafa

3. Resting Membrane Potential of the Neuronal Soma. • Resting Membrane Potential-65 millivolts. • Less negative than the -90 millivolts • Lower voltage is important: • Allows both positive and negative control of the degree of excitability of the neuron. • Decreasing the voltage - less negative value - neuron more excitable • Increasing the voltage - more negative value - neuron less excitable.

4. Resting Membrane Potential of the Neuronal Soma

5. The process of Synaptic Transmission

7. 40 nm vesicles formed in GA of cell body- Motor neuron Vesicles transported---axoplasmic streaming to nerve terminal Acetylcholine synthesized in terminal parts of nerve - stored Action potential opens calcium channels

8. Calcium bind with protein molecules (Release sites) Exocytosisof Acetylcholine vesicle 2000 and 10,000 molecules of acetylcholine are present in each vesicle Enough vesicles in the Presynaptic terminal To transmit more than 10,000 action potentials.

9. Acetylcholine. Acetyl cholinesterase Vesicles reformation Acetate Choline Coated pits - Clathrin Reabsorbed BACK New vesicles ACETYLCHOLINE (NT) IN SYNAPTIC CLEFT

11. Transmitter substance activates Ion ChannelSecond Msgr System

12. If transmitter substance activates an Ion Channel opens within a fraction of a millisecond Cation channelAnion Channel Sodium Ions Chloride ions Excitatory Transmitter Inhibitory Transmitter

13. “Second Messenger” System in the Postsynaptic Neuron. G Protein activation Alpha Beta Gamma Alpha

14. G Protein mediated actions • Opening specific ion channels • Activation of cAMP or cyclic cGMP in the neuronal cell. • Activation of one or more intracellular enzymes. • Activation of gene transcription.

15. If Post synaptic Neuron to be Excited

16. Excitation • Opening of Sodium Channels • Depressed conduction through Chloride or Potassium channels, or both. • Various changes in the internal metabolism of the postsynaptic neuron

17. Effect of Synaptic Excitation on the Postsynaptic Membrane • Increase the membrane’s permeability to Na+ • Neutralizes part of the negativity of the RMP • Positive increase in voltage above the RMP • Excitatory Postsynaptic Potential(or EPSP) • 20 millivolts more positive than RMP • simultaneous discharge of many terminals —about 40 to 80

18. EPSP

19. EPSP

20. If Post synaptic Neuron to be Inhibited

21. Inhibition • Opening of Chloride ion channels through the postsynaptic neuronal membrane. • Increase in conductance of potassium ions out of the neuron. • Activation of receptor enzymes that • Inhibit cellular metabolic functions • Increase the number of inhibitory synaptic receptorsor • Decrease the number of excitatory receptors.

22. Electrical Events During NeuronalInhibition • Open mainly Chloride channels • Potassium efflux • Increase the degree of intracellular negativity- Hyperpolarization • Inhibitory Postsynaptic Potential(IPSP) • More negative value of -70 millivolts • IPSP of -5 millivolts

23. IPSP

24. Function of Synapses • Ensure impulse to pass in one direction • Prevent damage of effectors due to over stimulation • Act as junctionsfor dividing up and merging of neurons

25. Let's see Today's Knowledge Gain

29. Resting Membrane Potential of the Neuronal Soma

30. EPSP

31. IPSP

32. Thank you