1. N ERVOUS S YSTEM 2.11.16 Neuron Physiology

2. N EURONS So, we know how neurons are structured (built) but how do they actually work? ACTION POTENTIALS

3. A CTION P OTENTIAL When a neuron is stimulated enough, it sends an electrical impulse down through the axon to the next neurons

4. A CTION P OTENTIAL Can only send one signal (the electrical impulse transmits and a uniform strength and speed), so how do we interpret different information from the neurons? They can very the frequency or number of pulses

5. A CTION P OTENTIAL Electricity Human bodies are electrically neutral Equal amounts of positive and negative charges occurring HOWEVER, Certain areas are more positively or negatively charged than others. THEREFORE, We have barriers to keep the positive and negative charges apart (because they are attracted to each other) UNTIL, we are ready to use the energy their attraction creates

6. A CTION P OTENTIAL Keep the charges separated to build potential

7. A CTION P OTENTIAL Example: Battery Has a positive and a negative end, but cannot do anything until connected to something that lets the charges move toward each other

8. A CTION P OTENTIAL

9. Voltage: Measure of potential energy generated by separated charges Normally measured in volts Measured in millivolts in people because such a small amount Call it membrane potential in people

10. A CTION POTENTIAL The GREATER the distance between charges, the HIGHER the voltage, and the LARGER the potential

11. A CTION P OTENTIAL Current The flow of electricity from one point to another The amount of charge in a current is related to its voltage and resistance Resistance is whatever is getting in the way of the current Example: plastic, high resistance (an insulator from electrical current) Example : metal, low resistance (a conductor for electrical current)

12. A CTION P OTENTIAL What does all of this have to do with people? Currents indicate the flow of negatively or positively charged ions across the resistance of your cells membranes Remember: membranes separate the charges, so they are what provide the potential to convert the electricity into something useful

13. A CTION P OTENTIAL Resting membrane potential: there is a positive charge outside the cell, and a negative charge inside the cell

14. A CTION P OTENTIAL Sodium ions provide the bulk of the positive charge outside the cell Proteins and phosphate ions provide the negative charge on the inside You still have some negative and positive ions on both sides though

15. A CTION P OTENTIAL Remember: it is about the difference in charge across the membrane Is -70millivolts in people Polarized

16. A CTION P OTENTIAL Sodium Potassium Pump

17. A CTION P OTENTIAL Sodium Potassium Pump Protein Straddles the membrane For every 2 Potassium (K+) ions it pumps in, it pumps 3 Sodium (Na+) ions out This creates a difference between the concentration of Na+ and K+ Because it pumps 3 positively charged ions out of the cell while only bringing 2 inside ELECTROCHEMICAL GRADIENT