How do neurons communicate?

1. How do neurons communicate?

2. a b c

3. How do neurons communicate? Need to think about this question 2 ways

4. How do neurons communicate? 1. within neurons – 2. between neurons-

5. Neuron receiving info Information traveling down neuron

6. How do neurons communicate • within neurons – electrically • between neurons – chemically • Synapse – space between neurons

7. Ramon Y Cajal • developed Golgi Stain • first determined space between neurons • “synapse”

8. Neurons can exist in one of 3 states • the “resting” state • the “active” state • neuron is firing • action potential • the “refractory” state

9. How do we know about what is happening in the neuron? • giant squid axon

12. At rest: • inside of the axon has a slightly negative charge relative to outside the axon • called the membrane potential • usually around -70mV

13. At rest: • inside of the axon has a slightly negative charge relative to outside the axon • called the membrane potential • why?

14. action potential or spike

16. Neuron stimulated (either electrically or by receiving a “message” • see depolarization (change from negative inside neuron to more positive)

17. action potential or spike

18. Neuron stimulated (either electrically or by receiving a “message” • see depolarization (change from negative inside neuron to more positive) • “threshold” – if a great enough depolarization occurs, an action potential will occur • action potential – very quick – milliseconds • Other terms – spike, firing, generating an AP

19. action potential or spike

20. Hyperpolarization • return to negative • this is the refractory or recovery period

21. action potential or spike

22. What causes these changes in electrical potential and the action potential? • All axons and cells have a membrane • thin lipid (fat) bilayer • The membranes have channels (to allow ions in or out) • Ions – molecules with a charge • These channels can be open or shut

24. What causes these changes in electrical potential? • Ions flowing across the membrane causes the changes in the potential • Ions are molecules that contain a positive or negative charge • anion – negative charge • cation – positive charge

25. Some important ions for neuronal communication • Na+ sodium • HIGHER CONCENTRATION OUTSIDE THE AXON • Cl- chloride • HIGHER CONCENTRATION OUTSIDE AXON • K+ potassium • higher concentration inside the axon • A- anions -large (-) molecules with a negative charge (stuck inside the axon)

26. OUTSIDE AXON (EXTRACELLULAR FLUID) INSIDE AXON (intracellular) Na+ Cl- Na+ A- Cl- Cl- A- Cl- Cl- Na+ Na+ Cl- Cl- A- Na+ Na+ A- Na+ Na+ Cl- A- Na+ Na+ Cl- Na+ Cl- Cl- Na+ A- Na+ Cl- Cl- Cl- Cl- Na+ and Cl- are in higher concentration in the extracellular fluid Neuron at Rest

27. INSIDE AXON OUTSIDE AXON (EXTRACELLULAR FLUID) Cl- K+ K+ K+ Cl- A- Na+ Cl- A- Na+ K+ Na+ A- Cl- Na+ K+ A- Na+ Cl- Na+ K+ K+ K+ and negative anions are in higher concentration in the intracellular or inside the axon Neuron at Rest

28. Some forces that play a role in maintaining membrane potential • concentration gradient – • ions diffuse from higher concentration to lower concentration

29. example of concentration forces

30. What would each ion do if the ion channel opened based on the concentration gradient?

31. Some forces that play a role in maintaining membrane potential • concentration gradient – • ions diffuse from higher concentration to lower concentration • electrical gradient - • opposite charges attract so ions are attracted to an environment that has a charge that is opposite of the charge they carry!

32. example of electrostatic forces

33. What would each ion do if the ion channel opened based on electrostatic forces ?

34. OUTSIDE AXON (EXTRACELLULAR FLUID) INSIDE AXON (intracellular) Na+ Cl- Na+ A- Cl- Cl- A- Cl- Cl- Na+ Na+ Cl- Cl- A- Na+ Na+ A- Na+ Na+ Cl- A- Na+ Na+ Cl- Na+ Cl- Cl- Na+ A- Na+ Cl- Cl- Cl- Cl- Na+ and Cl- are in higher concentration in the extracellular fluid Axon depolarizing

35. What drives the action potential? • opening of Na+ channels and influx of Na+ ions

36. What happens if sodium channels are blocked? • lidocaine, novocaine, cocaine • TTX – tetrototoxin • Sagitoxin- • red tides

38. Concentration Gradient Electrical Gradient after the AP (+ intracellular)

39. INSIDE AXON OUTSIDE AXON (EXTRACELLULAR FLUID) Cl- K+ K+ K+ Cl- A- Na+ Cl- A- Na+ K+ Na+ A- Cl- Na+ K+ A- Na+ Cl- Na+ K+ K+ K+ and negative anions are in higher concentration in the intracellular or inside the axon Neuron at Rest

40. Sodium-potassium pump – active force that exchanges 3 Na+ inside for 2 K+ outside

41. INSIDE AXON OUTSIDE AXON (EXTRACELLULAR FLUID) Cl- Na+ K+ K+ Cl- A- Na+ Cl- Na+ A- Na+ K+ Na+ A- Na+ Cl- Na+ K+ A- K+ Na+ Na+ Cl- Na+ K+ K+ Na+ K+ and negative anions are in higher concentration in the intracellular or inside the axon After the action potential

43. conduction or propogation of the action potential • myelin sheath (80% fat and 20% protein) • produced by glia

44. http://www.blackwellpublishing.com/matthews/channel.html

45. nodes of ranvier

46. conduction or propogation of the action potential • myelin sheath (80% fat and 20% protein) • produced by glia • nodes of ranvier

47. nodes of ranvier

48. conduction or propogation of the action potential • myelin sheath (80% fat and 20% protein) • produced by glia • nodes of ranvier • saltatory conduction (200 ft/sec)