4. Quick Review What’s another name for neurons? Can you name the parts of a neuron?

5. Review Questions How do nerve cells communicate with each other? Nerve cells are also called ____________ How many types of neurons are there? Which nervous system are they related to? What is a resting potential?

6. Taking a closer look at the AXON

9. Myelin Sheath A protective layer that wraps around the axon Allows impulse to travel faster Made by Schwann cells “Schwann cells myelinate parts of an axon” Gaps are called Nodes of Ranvier nerve impulses - - unmyelinated axons  1 m/s - myelinated axons  100 m/s.

10. Myelin Sheath in PNS Gives fibers their white glistening appearance Myelin serves as an excellent insulator Regenerate nerves Damaged axon may use myelin sheath as a passageway to regenerate new fiber in CNS Nerve regeneration does not occur

11. Myelinated Axon – in CNS 2 types of nervous tissue (Made up of many neurons): Gray matterWhite matter -gray because it contains cell bodies + short -Not myelinated -white because it contains myelinated axons -Carries messages from one part of the CNS to another -Lies deep within the gray matter (in the brain)

13. The Nerve Impulse Conveys messages in our body Unit: millivolts (mV) Measures the electrical potential difference (polarity) between 2 points

14. Saltatory Impulse Transmission Flow is due to ion movements at the nodes IONS: Electrically charged chemicals Na + (outside axon) K + Cl – Therefore, the voltage (mV) is created by the polarity (difference of charge) of the inside and outside of an axon (Inside axon) electrical potential difference

15. Saltatory Impulse Transmission Neurons have a semi-permeable membrane for ions to pass through Axomembrane: membrane of the axon - contain Na/K pumps and gates Axoplasm: cytoplasm of the axon (fluid inside the axon)

16. Saltatory Impulse Transmission “jumping” transmission

17. Saltatory Impulse Transmission When neurons (axon) are at rest – not sending a nerve impulse it is called the A neuron in the resting state is polarized Resting Potential is always negative on the inside of the axon (-65 mV) RESTING POTENTIAL

18. The Resting Potential At rest, axomembrane is NOT permeable to these ions because the gates are closed. Due to natural unequal distribution of ions a slight negative charge results [Na+] > [K+] outside

19. The Resting Potential Na/K pumps (proteins) are found on the axomembrane pumps Na+ out and K+ into the axon Keeps the unequal distribution of the ions Membrane is permeable to K+ therefore, it leaks out (outside is always more positive than inside)

21. The Action Potential Only takes 2 milliseconds Rapid change in polarity (electrical difference) Occurs when there is a intense stimulus that reach the threshold value ALL-OR-NONE (yes-impulse or none at all)

22. The Action Potential What happens next: 1. DEPOLARIZATION Na+ gates (in the axomembrane) becomes permeable to Na+ - Na+ moves down its concentration gradient into the axon - Membrane potential -65mV  +40mV 2. REPOLARIZATION K+ gates open - K+ moves down its concentration gradient out of the axon - Membrane potential reverts back to +40mV  -65mV - Since there is more negative ions inside compared to positive ions

25. Refractory Period Prevents the action potential from moving backwards During this period, Na+ gates can’t be opened The Na+/K+ pump is busy restoring the resting potential by pumping Na+ ions out and K+ ions in through the axomembrane.

28. Stop here