Electrical Signals in Neurons

1. Electrical Signals in Neurons Ch. 12-3

2. Mini-Physics Lesson Potential energy – energy stored in a system (the body) as a result of its position or chemical composition Kinetic energy – energy being used for motion or force

3. Physics to Anatomy Neurons are excitable because of a voltage difference across the membrane - potential “Potential” will initiate an impulse that can travel through the nervous system Graded potentials – used for short-distance communication Action potentials – allow communication over short and long distance within the body

4. Potential • Membrane potential – electrical voltage difference across the membrane • Resting membrane potential – membrane potential in an excitable cell • Like voltage stored in a battery • If + and – ends connect, electrons flow in a current • Current • Flow of charged particles • For the body – these are ions instead of elecrons

5. Ion Channels Gradient – difference Electrochemical gradient – difference in charge and concentration Positive cations move toward negative areas, negative anions move toward positive areas Ion location can be controlled with gates that can open or close the pore

6. Ion Channels Leakage channels Voltage-gated channels Ligand-gated channels Mechanically gated channels

7. Ion Channels • Leakage channels • Randomly open and close • most cells leak more potassium (K+) than sodium (Na+) • voltage-gated channels • Opens in response to a change in voltage (membrane potential) • Generate and conduct action potentials

8. Ion Channels • Ligand-gated channels • Opens and closes in response to chemical stimulus (nts, hormones, other ions – ligand molecule) • Ex: Ach opens channels that allow Na+ and Ca2+ to go in and K+ to go out • Work in 2 ways • ligand molecule can open or close the channel itself by binding • Ligand molecule activates another chemical messenger to open the channel

9. Ion Chanenls • Mechanically gated • Opens or closes in response to stimulation by: • Vibration: sound waves • Pressure: touch • Tissue stretching • The channel is physically disrupted and opens

10. Ion Channels

11. Resting Membrane Potential • Exists due to negative ions in cytosol (ICF) and equal positive ions in ECF • The greater the difference in charge, the larger the potential • Example: • 5 Na+ on outside, 4 Cl- on inside – small potential • 25 Na+ on outside, 4 Cl- on insdie – great potential

12. RMP • Most cells have potential between -40 to -90 mV; typical is -70mV • Minus sign means the cell is negative – not negative potential! • Any cell with potential is polarized • The potential varies between +5 to -100 mV

13. How does the potential get there? • ECF • Rich in Na+ and Cl- • ICF • Rich in K+ • Also has P-, amino acids,

14. RMP • Ion interaction • There are many K+ leakage channels, so K+ diffuse out • + ions exit, inside becomes more negative • - ions can’t leave because they are bound to molecules • - charges attract the K+ back in toward the cell • Few Na+ ions leak inward • This would destroy the membrane potential, so there are pumps that take care of this

15. Na+/K+ pump • To keep the RMP • Pump out Na+ as it leaks in • Pump in K+ as it leaks out • 3 Na+ for each 2 K+ - this still maintains a negative charge in the cell

16. RMP - Draw