Nervous System

1. Nervous System Pages 228-237 http://www.youtube.com/watch?v=FR4S1BqdFG4

2. Functions of the nervous system 1. Sensory input—gathering info • Monitor changes occurring inside & outside the body 2. Integration • Make sense of information &decide if/what action is needed 3. Motor output • The “response” • activates muscles or glands in response to the stimulus

3. Structural Classification of the NS • Central nervous system (CNS) • Brain • Spinal cord • Peripheral nervous system (PNS) • Nerves outside the brain and spinal cord • Spinal nerves • Cranial nerves

4. Functional Classification of the Peripheral NS • Sensory (afferent) division • Nerve fibers that carry information to the CNS • “On ramp” • Motor (efferent) division • Nerve fibers that carry impulses away from the CNS • Two subdivisions • Somatic nervous system = voluntary • Autonomic nervous system = involuntary

5. Organize these into a web… • Just introduced • Motor neurons/efferent nerves • Central nervous system • Peripheral nervous system • Nervous system • Sensory/afferent nervous system • Guess about what these mean and where on the web they fit • Somatic nervous system  controls skeletal muscles • Autonomic nervous system  controls _______ muscle

7. Practice… Do you have the gist? • In the scenario identify the sensory input, motor effect, and integration (not specifically stated). Also identify the role of the efferent and afferent divisions of the nervous system and explain which specific efferent/motor division is being used. • Fritz was putting a tray of cookies into the oven. The top of his hand accidently grazed the side of the oven and he quickly retracted his hand out of the oven.

8. What type of cells make up the brain? • Neurons • conduct nerve impulses • can’t divide  no mitosis are in G0 phase • 2 functions: irritiability & conductivity

9. Remember way back… • What do the words polarization and depolarization mean?

10. Neuron Anatomy • Dendrites • Can have a few or 60 • Receive messages from other neurons • Cell body/soma • Metabolic center • Axon • Can only have ONE • Sends the message from the cell body

11. http://www.youtube.com/watch?v=-SHBnExxub8 Neuron Anatomy http://www.youtube.com/watch?v=sjyI4CmBOA0 • Axon hillock (where AP is generated) and axon terminal (branches at the end of an axon that pass the message along) • Myelin sheath • Not present on every axon • Pain receptors don’t have myelin on their axons

12. Supporting Cells of the PNS • Schwann Cells • Form myelin sheaths around nerve fibers • MS (multiple sclerosis) attacks myelin sheaths, converts them to hard covers that can’t conduct electrical impulses  slurred speech, loss of balance, impaired vision, etc

13. Something to think about… • What is a Schwann cell? • What part of the NS does it support? • What structural part of the neuron can it form?

14. Recap • Why is having a myelin sheath an advantage? ***If 2 nerves are equal in diameter - the nerve with myelin can send an action potential at a speed of 100 meters/sec. - the nerve without myelin can send the action potential at a speed of 1 meter/sec • What is saltatory conduction?

15. BIG PICTURE • Why we need neurons to be able to make an electrical impulse (action potential) Remember these are NOT physically connected

16. Synaptic cleft… where a neuron meets another neuron (shown here), a gland, or a muscle

17. Neuron Physiology • At resting state the neurons are polarized • - inside of the neuron b/c cell has proteins that have – charges • Has K+ but not enough to balance out the – • + outside of the neuron b/c more Na+ • Neurons are selectively permeable • Contain ion channels • Voltage gated ion channels  open when there’s a change in charge

18. Making an Action Potential • A stimulus causes Na+ to flow into the neuron • If enough Na+ flows in, the neuron’s charge becomes more positive and becomes depolarized (not as negative) causing the nerve to send an electrical signal  action potential AKA nerve impulse • Sodium voltage-gated ion channels open and Na+ rushes in  make the inside very +

19. Making an Action Potential • Once one area is positive, the positive charge moves down the axon causing more Na+ channels to open • After Na+ enters, the ions channels for Na+ close but the inside is still very + • Sodium-potassium pumps then use ATP to move Na+ out of the neuron and K+ in to return the charges inside and outside of the neuron to “normal”  repolarization • All or Nothing Response • 1 action potential at a time  while neuron is recovering it is in a refractory period  no nerve impulses an be generated

20. Action Potentials in Myelinated vs. Not fibers • Myelinated fibers carry messages faster • Use saltatory conduction (charge jumps from node of Ranvier to node of Ranvier) • Non-myelinated fibers transmit AP’s slower b/c all ion channels must open and close • The larger the diameter of the axon the faster the signal moves • Squid diameter 500 micometer 56 mph • Human internal organ diameter 1 micrometer  4.5 mph • Nerve to human leg muscle 20 micometers  270 mph… WOW… thanks myelin No myelin http://184.171.162.94/images/prevjhy.php?u=Oi8vd3d3LnlvdXR1YmUuY29tL3dhdGNoP3Y9REplM18zWHNCT2c%3D&b=5

23. Animations of AP Generation • http://184.171.162.94/images/prevjhy.php?u=Oi8vd3d3LnlvdXR1YmUuY29tL3dhdGNoP3Y9aWZEMVlHMDdmQjg%3D&b=5 • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html • http://www.youtube.com/watch?v=FR4S1BqdFG4 • http://www.youtube.com/watch?v=YP_P6bYvEjE

24. Practice • In groups of 2-4 create an analogy that parallels the event that take place to create an action potential/nerve impulse • Consider • the initial locations of Na+ and K+ • the movement of Na+ while the action potential is being created • The movement of K+ immediately after the AP has been generated • How the levels of Na+ and K+ inside and outside of the cell is corrected after the AP has been transmitted

25. Step By Step… 1. A neuron is more negative inside the cell relative to the outside (polarized) • 2. A stimulus makes causes the cell’s charge to reach the threshold • 3. Na+ channels open and sodium floods into the cell in one section of the axon • 4. The Na+ channels in that area close but the region down the axon gets positive enough to reach threshold  Na+ channels open and sodium rushes in… this continues down the axon • 5. The K+ channels open and potassium diffuses out • 6.The cell becomes repolarized BUT K+ is concentrated outside and Na+ is concentrated inside… must swap! • 7. The sodium-potassium pumps move Na+ our of the neuron and K+ into the neuron

26. Collins Type 2 • Now that we’ve discussed how nerve impulses are made, explain how an action potential is generated • You should • explain what happens to the potassium and sodium ions • which does each ion starts where • how does each move • Discuss polarization, repolarization, and depolarization (use whatever forms of these words that you need) • Explain what the threshold is • Discuss the all or none firing