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Nervous System

Learn about how animals' nervous systems detect and transmit signals, and how neurons play a crucial role in this process. Discover the importance of myelin sheaths, the concept of resting potential, and how nerve impulses travel through neurons. Gain insights into the action potential and how synapses facilitate the transmission of impulses.

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Nervous System

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  1. Nervous System

  2. Essential Knowledge: Animals have nervous systems that detect external and internal signals, transmit and integrate information and produce responses.

  3. Nervous system cells • Neuron • a nerve cell signal direction dendrites • Structure fits function • many entry points for signal • one path out • transmits signal cellbody axon signal direction synaptic terminal myelin sheath dendrite  cell body  axon synapse

  4. Myelin sheath • Axon coated with Schwann cells • Insulation material (lipid) • speeds up signal • saltatory conduction • 150 m/sec vs. 5 m/sec(330 mph vs. 11 mph) signal direction myelinsheath

  5. action potential saltatory conduction Na+ myelin + – axon + + + – + Na+ • Multiple Sclerosis • immune system (T cells) attack myelin sheath • loss of signal

  6. Neuron Functional Differences Integrates and coordinates info from afferent, sends out response to efferent

  7. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + – – – – – – – – – – – – – – – – – – – – – – – – – – – – Neuron at Resting Potential • Opposite charges on opposite sides of cell membrane • membrane is polarized • negative inside; positive outside • charge gradient (-70mv) • stored energy (like a battery)

  8. Na+ Na+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ Cl- Cl- Cl- aa- aa- K+ aa- Cl- aa- aa- aa- K+ Cl- Cl- What makes it polarized? • Cells live in a sea of charged ions • anions (negative) • more concentrated within the cell • Cl-, charged amino acids (aa-) • cations (positive) • Na+ more concentrated in the extracellular fluid Salty Banana! channel leaks K+ K+ + – K+

  9. + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – Na+ How does a nerve impulse travel? • Stimulus: nerve is stimulated • reaches threshold potential • open Na+ channels in cell membrane • Na+ ions diffuse into cell • charges reverse at that point on neuron • positive inside; negative outside • cell becomes depolarized The 1stdomino goesdown!

  10. Gate + + – + channel closed channel open + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – Na+ wave  Depolarization • Wave: nerve impulse travels down neuron • change in charge opens next Na+ gates down the line • “voltage-gated” channels • Na+ continues to diffuse down neuron • “wave” moves down neuron = action potential The restof thedominoes fall!

  11. Voltage-gated channels • Ion channels open & close in response to changes in charge across membrane Structure& function!

  12. K+ + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – Na+ wave  Repolarization • Re-set: 2nd wave travels down neuron • K+ channels open • K+ channels open up more slowly than Na+ channels • K+ ions diffuse out of cell • charges reverse back at that point • negative inside; positive outside Setdominoesback upquickly!

  13. K+ + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – Na+ wave  How does a nerve impulse travel? • wave of opening ion channels moves down neuron • flow of K+ out of cell stops activation of Na+ channels in wrong direction Animation Readyfornext time!

  14. How does the nerve re-set itself? • Sodium-Potassium pump • active transport protein in membrane • requires ATP • 3 Na+ pumped out • 2 K+ pumped in • re-sets chargeacross membrane ATP That’s a lot of ATP ! Feed me somesugar quick!

  15. Action potential graph • Resting potential • Stimulus reaches threshold potential • DepolarizationNa+ channels open; K+ channels closed • Na+ channels close; K+ channels open • Repolarizationreset charge gradient • UndershootK+ channels close slowly 40 mV 4 30 mV 20 mV Depolarization Na+ flows in Repolarization K+flows out 10 mV 0 mV –10 mV 3 5 Membrane potential –20 mV –30 mV –40 mV Hyperpolarization (undershoot) Threshold –50 mV –60 mV 2 –70 mV 1 6 Resting Resting potential –80 mV

  16. All or nothing response • Once first one is opened, the rest openin succession • a “wave” action travels along neuron • have to re-set channels so neuron can react again How is a nerve impulse similar to playing with dominoes?

  17. What happens at the end of the axon? Synapse Impulse has to jump the synapse! • junction between neurons • has to jump quickly from one cell to next How does the wavejump the gap?

  18. The Synapse • Action potential depolarizes membrane • Opens Ca++ channels • Neurotransmitter vesicles fuse with membrane • Release neurotransmitter to synapse  diffusion • Neurotransmitter binds with protein receptor • ion-gated channels open • Neurotransmitter degraded or reabsorbed axon terminal action potential synaptic vesicles synapse Ca++ neurotransmitteracetylcholine (ACh) receptor protein muscle cell (fiber) We switched… from an electrical signal to a chemical signal

  19. Neurotransmitters • Acetylcholine • transmit signal to skeletal muscle • Epinephrine (adrenaline) & norepinephrine • fight-or-flight response • Dopamine • affects sleep, mood, attention & learning • lack of dopamine in brain associated with Parkinson’s disease • excessive dopamine linked to schizophrenia • Serotonin • affects sleep, mood, attention & learning

  20. Weak point of nervous system • Any substance that affects neurotransmitters or mimics them affects nerve function • Ex: Gases,drugs, poisons • Acetylcholinesterase inhibitors = neurotoxins! • Ex: snake venom, insecticides Snake toxin blockingacetylcholinesterase active site

  21. Vertebrate Brains • Evolutionary trends towards “Cephalization” • Central region for integrating and coordinating information. • Different regions have different functions:

  22. How are they similar? How are they different? More mass, more neurons, more connections….

  23. Ponder this…Any Questions??

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