2. PHYSIOLOGY OF THE NERVOUS SYSTEM

3. Neurons are IRRITABLE Ability to respond to a stimulus! (What’s a stimulus?)

4. How do neurons respond to stimuli? By generating an ACTION POTENTIAL! Action Potential = “Nerve Impulse” Reminder: Which part of the neuron generates impulses? NOTE: –A stimulus must be strong enough (above the threshold level) to generate an Action Potential –Examples…

5. So how does an Action Potential get generated??? Involves: 1. Ions 2. Ion Channels in Neuron Membranes 3. Electricity! (Currents, Voltage)

6. 1. Ions Involved: K + Na+ Cl - Ca++ Various Anions (A - )

8. 2. Ion Channels Transport Proteins embedded in Phospholipid Membrane of Axon! 2 Major Types: –Passive (Leakage) Channels –Active (Gated) Channels: Voltage-Gated Channels Chemically-Gated Channels Mechanically-Gated Channels

9. The Big Idea AN ELECTRICAL IMPULSE IS GENERATED WHEN IONS MOVE ACROSS THE AXON MEMBRANE THROUGH OPEN CHANNELS!!

10. 3. ELECTRICITY Overall, –The body is Electrically Neutral! ( # + charges = # - charges)

11. Voltage Measures the Potential Energy due to separation of charges across a membrane! Current Flow of electrical charge from one point to another. Can be used to do WORK!! (Kinetic Energy)

14. When Charges are Separated Across the Neuron Membrane… Neuron is “AT REST” –( Potential Energy, Kinetic Energy) RESTING MEMBRANE POTENTIAL: –Separation of Charge across membrane… –More (-) charges inside than (+) outside –Voltage Reading = –70 millivolts –Membrane is POLARIZED !

15. Resting Membrane Potential The Polarized State

16. What Maintains the Resting Membrane Potential? Maintaining the differences in [ion] between the intracellular and extracellular fluids!!

17. Distribution of Ions during Resting Potential State K + : inside membrane Na+ : outside membrane Cl - : outside membrane Various Anions (A - ) : inside membrane

18. Permeability Across the Membrane K+ Na+ Cl- Anions- High Permeability (Leakage Channels) Low Permeability High Permeability IMPERMEABLE!!!

20. The Sodium Potassium Pump K+ constantly leaks across membrane to outside! ( Why?) K+ pumped back into cell! Na+ pumped out of cell! Ratio : 3 Na+ OUT / 2 K+ IN ACTIVE TRANSPORT MECHANISM!! (What does that mean??)

22. Let the Fun Begin… Generation of a Nerve Impulse 1.Signal is detected/received and relayed to axon membrane. 2.RESTING MEMBRANE POTENTIAL ACTION POTENTIAL!! (aka: Nerve Impulse!)

23. Action Potentials Caused by a shift in membrane potentials along the axon! Detection of STIMULUS Shift in Membrane Permeabilities!

24. So what’s the deal with Action Potentials? An Action Potential (AP) is: a wave of positive charges that travel undiminished in strength along the axon

25. The Chain of Events 1.Stimulus is detected 2.Gated Ion Channels open 3.Na+ rushes into the cell 4.Charge on cell membrane becomes DEPOLARIZED ( -70 mv  0 mv)

27. 5.If stimulus is strong enough (above THRESHOLD LEVEL), MORE Na+ GATES OPEN!! 6.Complete DEPOLARIZATION occurs! (-70mv  0mv  +30mv)

29. 7.Na+ channels open further down the neuron 8.AP travels down length of neuron!

31. Action Potentials are ALL OR NOTHING !!! IF A STIMULUS DOES NOT REACH THRESHOLD LEVEL…. NO AP! IF A STIMULUS REACHES THRESHOLD LEVEL, AP IS GENERATED AND TRAVELS DOWN LENGTH OF THE AXON!!!

33. http://www.stolaf.edu/people/giannini/fla shanimat/transport/secondary%20active %20transport.swf