What about communication between neurons?

1. What about communication between neurons?

3. Some terms……. • presynaptic ending – • portion of the axon conveying information to the next neuron

5. Some terms……. • presynaptic ending – • the portion of the axon that is conveying information to the next neuron • synapse or synaptic cleft • the space between neurons where communication occurs

7. Some terms……. • presynaptic ending – • the portion of the axon that is conveying information to the next neuron • synapse or synaptic cleft • the space between neurons where communication occurs • postsynaptic membrane • the portion of the neuron (usually dendrite) that receives information

9. Some terms……. • presynaptic ending – • the portion of the axon that is conveying information to the next neuron • synapse or synaptic cleft • the space between neurons where communication occurs • postsynaptic membrane • the portion of the neuron (usually dendrite) that receives information • pre and postsynaptic receptors • proteins in both the presynaptic and postsynaptic ending that allow for information to be transferred

11. synaptic vesicles --small enclosed membranes that contain neurotransmitter - found in presynaptic ending • neurotransmitter – substance in vesicles that are released in synapse and convey info to the next neuron

12. Presynaptic ending synapse Postsynaptic ending

13. What happens at level of synapse? • AP reaches presynaptic ending- • Ca+2 channels in presynaptic ending open and Ca+2 enters

14. Why are Ca+2 ions important? Ca+2 entry into the presynaptic ending critical for neurotransmitter release

16. drugs that block Ca+2 channels…….

17. postsynaptic receptors • protein embedded in membrane • mechanism for neurotransmitter to influence postsynaptic activity by binding to receptor

18. Summary • NT binds to postsynaptic receptors and causes small local changes in electrical potential (depolarizations or hyperpolarizations)- • Called graded potentials

19. Graded Potentials • increase or decrease the likelihood of the neuron receiving info to generate an action potential • graded potentials that increase the likelihood of an action potential are called EPSPs (excitatory postsynaptic potentials)

21. Graded Potentials • increase or decrease the likelihood of the neuron receiving info to generate an action potential • graded potentials that increase the likelihood of an action potential are called EPSPs (excitatory postsynaptic potentials) • graded potentials that decrease the likelihood of an action potential are called IPSPs (inhibitory postsynaptic potentials)

23. How does the neurotransmitter cause EPSPs and IPSPs? • NT binding to postsynaptic receptors cause local ion channels to open • chemically dependent ion channels • (in contrast with electrically dependent ion channels in the axon)

24. How does the neurotransmitter cause EPSPs and IPSPs? • postsynaptic receptors open ion channels – • ion channels in postsynaptic membrane (that we need to worry about) include Na+, Cl- and K+

25. Two kinds of Graded Potentials • EPSPs – excitatory postsynaptic potentials • - increase the likelihood of an AP • - opening of • IPSPs – inhibitory postsynaptic potentials • decrease the likelihood of an AP • - opening of

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27. Axon hillock

28. How do graded potentials result in an action potential? • graded potentials are summed at axon hillock and……if the sum is a great enough depolarization….

30. action potential or spike

31. Graded potentials vs action potentials • Graded Potentials and AP differ in a number of ways • AP – occurs at the axon • GP – occurs anywhere the neuron receives info from another neuron (usually dendrite although NOT ALWAYS) • action potentials are “all or none” graded potentials decrease over space and time • Graded potentials are localized – has impact in limited region; AP travels down the axon

32. Graded vs Action Potentials • Graded potentials can either increase or decrease the likelihood of an action potential

34. So what about these NT? • Postsynaptic receptor and NT – think about a lock and key!

35. Neurotransmitter represents a key Receptor represents the lock

36. 2 ways that neurotransmitter exert these effects • directly opening the ion channel • occurs and terminates very quickly

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39. 2 ways that neurotransmitter exert these effects • directly opening the ion channel • occurs and terminates very quickly • more indirect • ultimately opens ion channel via stimulating a chemical reaction • takes longer but lasts longer

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42. 2 main ways for getting the neurotransmitter out of the synapse 1. reuptake - most common • protein on presynaptic ending transports it back into the neuron that released it • Means of recycling NT • saving energy (neurons have to synthesize or produce their own NT) • a common way for drugs to alter normal communication

43. Examples of reuptake inhibitors cocaine, amphetamine, methylphenidate (Ritalin) – block reuptake of a number of NT – particularly dopamine (reward) many of the newer antidepressants are SSRIs (selective serotonin reuptake inhibitors)

44. enzyme degradation • enzyme - speeds up a reaction • ex. acetylcholine (ACh)is a neurotransmitter is broken down by acetylcholinesterase (AChE) • For ACh – this is done in the synapse

45. Neurotransmitters • probably 100s of “putative” neurotransmitters – more being discovered all the time • role that the novel NTs play still being determined

46. Some classic NT • acetylcholine (ACh) –

47. Some classic NT acetylcholine (ACh) – found in CNS and PNS • receptor subtypes – • nicotinic and muscarinic

48. Some classic NTs acetylcholine (ACh) – found in CNS and PNS • receptor subtypes – • nicotinic and muscarinic • nicotinic receptors – muscles • acetylcholine also important for various behaviors including learning and memory alzheimers disease, REM sleep, among other things…

49. Neurotransmitters (cont) • Monoamines • dopamine (DA) important for reward circuits schizophrenia and Parkinsons disease

50. Neurotransmitters (cont) • Monoamines • dopamine (DA) • norepinephrine (NE) important for arousal altered activity implicated in depression