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DO NOW

DO NOW. Why do frog legs twitch when you add salt (sodium)? Draw the action potential graph and label depolarization and repolarization. GRAB YOUR GREEN FOLDER!!! You have 5 minutes . IN YOUR SEATS. Paper and pencil out. Noise level 1. COMPLETE SENTENCES!!!

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DO NOW

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  1. DO NOW Why do frog legs twitch when you add salt (sodium)? Draw the action potential graph and label depolarization and repolarization. GRAB YOUR GREEN FOLDER!!! You have 5 minutes. IN YOUR SEATS. Paper and pencil out. Noise level 1. COMPLETE SENTENCES!!! Write down the I CAN’s and Agenda if you finish early.

  2. DO NOW If you were an electrical impulse what would be the 4 things you see as you travel through the neuron, from first to last? Which division of the nervous system is “fight or flight” and which is “rest and digest” ? Which neuroglia destroys foreign invaders? GRAB YOUR GREEN FOLDER!!! You have 5 minutes. IN YOUR SEATS. Paper and pencil out. Noise level 1. COMPLETE SENTENCES!!! Write down the I CAN’s and Agenda if you finish early.

  3. Action potentials

  4. Frog Legs, Anyone? • https://www.youtube.com/watch?v=2YZJt_Bw3eo • https://www.youtube.com/watch?v=b79loRYPPBQ

  5. Why did the frog legs twitch? • Action potentials are the PHYSIOLOGY behind how electrical signals travel through the neuron (how the brain communicates with the rest of the body) • Cells have different charges inside and outside the cell because they have different ion concentrations  membrane potential (electrical charge!) • Two main ions: positive (+) charge • Sodium: Na+ • Potassium: K+

  6. Remember this? Diffusion & Homeostasis • Ions want to move to the less crowded side (lower concentration) until they reach homeostasis (both sides are equally crowded)

  7. Resting Potential • Because of the natural chemistry of the body, neurons have a resting potential of about -70mV: • More sodium ions outside the cell (evolution: came from salt water environment) • To maintain this difference in ion concentration across the cell membrane, neurons use the Sodium-Potassium Pump: 3 Na+ OUT/2 K+ IN  more positive charge OUTSIDE • More sodium molecules OUTSIDE, more potassium INSIDE • This takes ENERGY (ATP)  moving against concentration gradient At resting potential: • Inside axon: negative charge • Outside axon: positive charge

  8. Animation: The Nerve Impulse (Action Potential) http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

  9. Ready, Set, Action Potential! A disturbance (mechanical, electrical, or sometimes chemical) causes a few sodium channels in a small portion of the membrane to open. Sodium (Na+)ions enter the cell through the open sodium gates. The positive charge that they carry makes the inside of the cell slightly less negative When the depolarization reaches a certain threshold value (about -50mV to -55 mV), an action potential is triggered in an ALL OR NONE response (like shooting a gun).

  10. Action Potential Pt. II 4. Once threshold potential is reached, the sodium gates fling wide open, causing sodium (Na+) to rapidly flood into the cell. • WHY? Sodium ions want to move to the less crowded side  INSIDE the cell 5. This flow of sodium ions reverses the membrane potential in that area, making it positive inside the cell and negative outside — the electrical potential inside the cell increases to about +40 mV (DEPOLARIZATION)

  11. Action Potential Pt. III 6. Once the inside of the cell reaches about +40 mV, potassium channels are opened, which leads to potassium (K+) rapidly leaving the cell. This REPOLARIZES the cell  makes cell potential more negative again • WHY? Potassium wants to move to the less crowded side OUTSIDE the cell 7. Potassium gates are slow to close (“leaky”), leading to more potassium ions leaving than at resting. This causes HYPERPOLARIZATION – the inside of the cell becomes more negative than resting potential to about -90 mV • This prevents signals from traveling backwards since it is further away from threshold potential. It also contributes to the all-or-none response. 8. The sodium-potassium pump restores the cell to resting potential (-70 mV) • requires ATP: ions moving against concentration gradient

  12. GRAPH IT!

  13. Action Potential Links Axn Potential Graph http://bcs.whfreeman.com/thelifewire/content/chp44/4402s.swf http://www.wellcome.ac.uk/Education-resources/Education-and-learning/Big-Picture/All-issues/Inside-the-brain/WTS040399.htm http://www.sumanasinc.com/webcontent/animations/content/action_potential.html

  14. Ease on Down the Road… The electrical signal travels along the axon until it reaches the axon terminal  stimulates the release of neurotransmitters from vesicles Myelinated Axons conduct signals faster than unmyelinated axons because they “jump” along Nodes of Ranvier, increasing velocity.

  15. Action Potential Links Axn Potential Animated Overview http://outreach.mcb.harvard.edu/animations/actionpotential_short.swf Nerve Signaling Overview http://www.nobelprize.org/educational/medicine/nerve_signaling/game/nerve_signaling.html#/plot18 http://www.wellcome.ac.uk/Education-resources/Education-and-learning/Big-Picture/All-issues/Inside-the-brain/WTS040399.htm http://www.sumanasinc.com/webcontent/animations/content/action_potential.html

  16. So why did the frog legs twitch?

  17. Remember…Types of Nerves Sensory Neuron - conduct impulses brain or spinal cord (afferent impulse) Motor Neuron – conduct impulses muscles or glands (efferent impulse) Interneuron – conduct signal neuron  neuron

  18. Reflexes: Neurons in Action! • Reflex – rapid, predictable, and involuntary response to stimuli • Reflex arc – direct route from a sensory neuron, to an interneuron in the spinal cord, to a motor neuron, without brain input • Knee-jerk reflex - maintains balance/posture • Withdrawal reflex - avoidance of painful stimuli

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