1. The ins and outs of ions in the nervous system
Russian National Research Medical University
The ins and outs of ions in the nervous system
Abakumov M.A.
Moscow, 2015

3. Cell interactions in nervous system

4. Cell interactions in nervous system
Astrocytes – green Neurons – red

5. Neuron structure Dendrites Cell Body Axon Myelin Sheath Axon Node of
Ranvier

6. Signal transduction through neurons
Cells sustain transmembrane potential
Positive charge is at the outer side of membrane
Negative charge is at the inner side of the membrane
Change in transmembrane potential counts as a current and creates nerve impulse

7. Signal transduction through neurons
At resting state transmembrane potential is not changed and equal to -70mV
At resting state no signal is transducted + - V
-70mV

8. Signal transduction through neurons
Transmembrane potential is sustained due to electrochemical gradient of K+ and Na+ ions
Different concentration of K+ and Na+ ions is sustained by ATP dependent Sodium-Potassium Pump

9. Sodium-Potassium Pump
Uses energy of 1 ATP to transport 3 Na+ out and 2 K+ inside of the cell.
70% energy consumed by neuron is required for this
Runs anytime while not conducting an impulse
Creates high [Na+] outside and high [K+] inside

10. Signal transduction through neurons. Membrane ion channels
Transmembrane potential can be changed by opening of ion selective membrane channels
Allow ion movement, thus changing transmembrane potential
Specific to one type of ions

11. Membrane ion channels Passive Always open Provide free flow Active
Open/close in response to external signal
Ligand gated:
Open in response to ligand binding
Located on any cell membrane
Voltage gated:
Open/close in response to change in transmembrane potential
Located on axolemma and sarcolemma
Mechanically gated:
opens after membrane distortion
Located on sensory neurons for touch, pressure, vibration

12. Activatible sodium ion channel

13. Sodium selective ion channels
Opening leads to Na+ flow into the cell
Na+ flow favored by:
1) Chemical gradient
2) Electrical gradient
Makes cell less negative
This process is called depolarization
Na+ equlibrium potential is +66 mV

14. Potassium selective ion channels
Opening leads to K+ flow out of the cell
K+ flow favored by chemical gradient
Electrical gradient repels to K+ movement
Makes cell more negative
This process is called hyperpolarization
K+ equlibrium potential is -90 mV

15. Ion transmembrane movement in signal transduction
Open channel →ion flow→current→graded potential
Graded potential is a localized shift in transmembrane potential due to movement of charges

16. Graded potential Occur on any membrane
Can be depolarizing or hyperpolarizing
Amount of depolarization depends on intense of external stimuli
Passive spread from stimulation site by diffusion
Effect decreases with distance from stimulation site
Repolarization occurs as soon as stimuli is removed by leak channels and Na+/K+ pump

17. Action potential Occur on axolemma and sarcolemma
Can be only depolarizing
Starts only after threshold voltage (-55mV) is reached
Effect for stimuli exceeding threshold will be the same (“all-or-none”)
Passive spread from stimulation site by diffusion
Action potential at one site depolarizes neighboring site
Propagates through all membrane without decrease

18. Ion transmembrane movement in signal transduction

19. Ion transmembrane movement in signal transduction

20. Signal propagation through the axon
Propagation is a transmission of action potential
Continuous conduction - propagation of an action potential in a step-by-step depolarization of each adjacent area of an axon membrane
Saltatory conduction - propagation of an action potential along exposed portions of a myelinated nerve fiber; "jumping" node to node

21. Continious propagation

22. Saltatory propagation

23. Neuron structure Dendrites Cell Body Axon Myelin Sheath Axon Node of
Ranvier

24. Myelin and its structure

25. Myelin and its structure

26. Myelin and its structure.

27. Myelin and its structure. CNS.

28. Myelin and its structure. PNS.

29. Myelin composition. Water – 40% Dry mass: 1) Lipids (70-85%)
2) Proteins (30-15%)
Typical lipid for myelin are cerebroside and sulfatide
Typical proteins for myelin are myelin basic protein (MBP) and proteolipid protein (PLP)
Other myelin specific proteins are: 2′:3′- cyclic nucleotide 3′-phosphodiesterase (CNP) and myelin-associated glycoprotein (MAG)

30. Myelin composition. Cerebroside and sulfatide

31. Myelin composition. Myelin basic protein (MBP)
Highlu conserved gene
Localized at cytoplasmic surface of major dense line.
Stabilize major dense line by interacting with negatively charged phospholipids

32. Myelin composition. Proteolipid protein (PLP)
Tetraspan transmembrane protein. Both N- and C-ends are on cytoplasmic site.
Stabilizing intraperiod line of CNS myelin
Determines membrane spacing

33. Myelin composition. Myelin-associated glycoprotein (MAG)
Conytains single transmembrane domain
Located on periaxonal glial membranes of myelin sheats
Involved in interactions between glia and axons

34. Myelin composition. Compartmentalization.

35. Ion channels distribution in myelinated axon
Sodium channels are located at the beginnig of axon and at the Ranvier nodes.
Potassium channels are located under the myelin sheath closer to node of Ranvier