1. The Neuron & Action Potential The basic building block of our nervous system and how it sends messages.

2. Cell Body & Nucleus

3. The Cell Body –round, centrally located structure –contains DNA –controls protein manufacturing –directs metabolism –no role in neural signaling Contains the cell’s nucleus

4. Dendrites

5. Information collectors or receivers Receive inputs or signals from neighboring neurons Inputs may number in thousands If enough inputs the cell’s AXON may generate an electrical output

6. Dendritic Growth Mature neurons generally can’t divide But new dendrites can grow Provides room for more connections to other neurons New connections are basis for learning Studies show people with higher education have more dendritic connections than someone that is a high school dropout.

7. Neural Networks

8. Axon

9. Where all the action is Action Potential takes place – electrical charge is sent down the axon. One axon per cell, 2 distinct parts –tube-like structure –branches at end (axon terminals) that branch out to dendrites of other cells

10. Myelin Sheath & Nodes of Ranvier

11. Myelin Sheath White fatty casing on axon Acts as an electrical insulator Not present on all cells When present, increases the speed of neural signals down the axon allowing the action potential to “jump” to each Node of Ranvier - like a paved highway (see video below to compare mylenated axons vs. non-mylenated axons If this degenerates (dirt road), you have multiple sclerosis and can’t control your muscles. If time view this in a video click on the web address below (it will use QuickTime): Mylenated Axon

12. Axon Terminal or Buttons Axon Terminals

13. Axon Terminal or Buttons This is where the electrical impulse triggers synaptic transmission to the dendrites of a receiving neuron. Let’s Review with this Quick Video.Quick Video

14. Glial Cells They are the janitors of the neuron. Support cells that provide neurons with structural support and nutrition. They also remove cell wastes and enhance the speed of the neuron

15. Action Potential How neurons send an electrical message

16. How Neurons Communicate Neurons communicate by means of an electrical signal called the Action Potential Action Potentials are based on movements of ions between the outside and inside of the axon When an Action Potential occurs, a molecular message is sent to neighboring neurons Action Potential is an All or Nothing Process (like a gun firing)

17. Threshold: Triggering Action Potential  When a neuron is resting there is a balance of excitatory and inhibitory signals.  When one of these exceeds the other stimulus threshold is reached triggering the neuron to transmit an electrical impulse down its axon (action potential)  How do you feel something that is intense?  More neurons fire, the intensity of their electric impulse always stays the same.  Lou Gehrig’s Disease - too many inhibitory stimuli cause the muscles to freeze up.  Parkinson’s Disease - too many excitatory stimuli cause the muscles to move without control.

18. Steps to Action Potential

19. Resting Potential At rest, the inside of the cell is at -70 microvolts With inputs to dendrites inside becomes more positive If resting potential rises above threshold, an action potential starts to travel from cell body down the axon Figure shows resting axon being approached by an AP Axon at Resting Potential - fluid inside the axon is mostly negatively charged with positive on the outside (polarized)

20. Step 1: Threshold is Reached An impulse is triggered in the neuron’s dendrite when stimulated by pressure, heat, light or a chemical messenger from another neuron (stimulus threshold). This minimal level of stimulation that causes the axon to fire is called Stimulus Threshold

21. Step 2: Action Potential Begins When neuron fires, its axon membrane is selectively permeable. Gates in the axon called ion channels open allowing positive sodium ions to enter the axon while potassium ions leave giving it a brief positive electrical charge the axon (depolarized). The brief positive charge is action potential.

22. Depolarization Ahead of AP AP opens cell membrane to allow sodium (Na + ) in Inside of cell rapidly becomes more positive than outside This depolarization travels down the axon as leading edge of the AP

23. Step 3: Refractory Period As the next gates open allowing positive sodium ions in, the previous gates close and begin to pump the positively charged sodium ions out of the axon and potassium ions back inside. (repolarized). This step is called the refractory period and the axon cannot fire again until it returns to resting potential (negative polarized state). The entire process is like falling dominoes all the way down the axon except these dominoes can set themselves back up as soon as they fall over. Why do you think the axon has to set itself back to a resting state so quickly (3 milliseconds)? So the neuron can fire again and send another message immediately after the last one.

24. Repolarization follows After depolarization potassium (K + ) moves out restoring the inside to a negative voltage This is called repolarization The rapid depolarization and repolarization produce a pattern called a spike discharge

25. Finally, Hyperpolarization Repolarization leads to a voltage below the resting potential, called hyperpolarization Now neuron cannot produce a new action potential This is the refractory period

26. Action Potential Within a Neuron

30. Animated Action Potential To review this entire process click on the link for a short video that helps explain this complex process:short video

31. DAILY DOUBLE

32. How can a toilet represent Action Potential? Full Toilet – Resting Potential Push Flush Lever – Threshold Stimulus triggering Action Potential. Toilet Refilling/Can’t Flush – Repolarization/Refractory Period Sewer Pipes – One-way communication like action potential only goes from dendrite end to axon terminal end.