Nervous system


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Nervous system

  1. 1. The Nervous System
  2. 2. Facts: <ul><li>Responsible for all behavior </li></ul><ul><li>Every thought, action, and behavior controlled here </li></ul><ul><li>Works together with the endocrine system to achieve homeostasis </li></ul><ul><li>Cells communicate by electrical signals </li></ul>
  3. 3. Three Main Functions: <ul><li>Sensory input </li></ul><ul><li>Integration </li></ul><ul><li>Motor output </li></ul>
  4. 4. Sensory Input <ul><li>Our bodies have millions of sensory receptors </li></ul><ul><li>They detect changes </li></ul><ul><li>Changes are called “stimulus” </li></ul><ul><li>This is where all stimuli is collected </li></ul><ul><li>Called the “afferent pathway” </li></ul>
  5. 5. Integration <ul><li>Your brain makes decisions about what to do with the stimulus </li></ul><ul><li>It processes the info gathered </li></ul><ul><li>It establishes a set point </li></ul>
  6. 6. Motor Output <ul><li>Causes a response to the stimulus </li></ul><ul><li>Activates effector organs </li></ul><ul><li>Sends signal down “efferent pathway” </li></ul>
  7. 7. Nervous System Divisions <ul><li>Central Nervous System (CNS) </li></ul><ul><li>CNS includes brain & spinal cord </li></ul><ul><li>Peripheral Nervous System (PNS)’ </li></ul><ul><li>PNS broken down into afferent & efferent divisions </li></ul><ul><li>Sensory division = Afferent division </li></ul><ul><li>Motor division = efferent division </li></ul><ul><li>Both CNS and PNS work together </li></ul><ul><li>You can’t have one without the other </li></ul>
  8. 8. Nervous System Histology <ul><li>Nervous tissue is highly cellular </li></ul><ul><li>Less than 20% of cns is extra-cellular space </li></ul><ul><li>Cells densely packed together </li></ul><ul><li>Tissue is made up of two principal types of cells (nerve cells and supporting cells) </li></ul>
  9. 9. Supporting Cells in CNS <ul><li>Glial cells (neuroglia) </li></ul><ul><li>Glial cells have branching processes and central cell body, like neurons </li></ul><ul><li>Smaller than neurons </li></ul><ul><li>Outnumber neurons in CNS 9 to 1 </li></ul><ul><li>They make up half the mass of the brain </li></ul>
  10. 10. Common Glial Cells in CNS <ul><li>Astrocytes </li></ul><ul><li>Control chemical enironment around neurons </li></ul><ul><li>“ mop up” leaked potassium ions & recycle them </li></ul><ul><li>Recapture/recycle neurotransmitters </li></ul><ul><li>Microglia </li></ul><ul><li>Monitor health of neurons </li></ul><ul><li>Protect against microorganisms </li></ul><ul><li>Can turn into macrophages which destroy foreign intruders </li></ul><ul><li>Fact: immune system cells are denied access to CNS </li></ul><ul><li>Oligodendrocytes </li></ul><ul><li>Make up myelin sheaths </li></ul>
  11. 11. Supporting Cells in PNS <ul><li>Satellite Cells </li></ul><ul><li>Surround neuron cell bodies </li></ul><ul><li>Play a role in controlling the chemical environment of the neurons </li></ul><ul><li>Schwann Cells </li></ul><ul><li>Surrounds & forms myelin sheaths around larger nerve fibers in PNS </li></ul><ul><li>Functionally similar to oligodendrocytes </li></ul>
  12. 12. Neurons <ul><li>Structural units of the nervous system </li></ul><ul><li>Highly specialized cells </li></ul><ul><li>Have extreme longevity with good nutrition (100 years plus) </li></ul><ul><li>Neurons are amitotic - no ability for mitosis. Cannot be replaced if destroyed </li></ul><ul><li>Have a high metabolic rate - need high amounts of oxygen & glucose. </li></ul><ul><li>Cannot survive more than a few minutes without oxygen </li></ul>
  13. 13. Neuron Anatomy <ul><li>The most common neuron is multipolar </li></ul><ul><li>They are made up of four basic parts: </li></ul><ul><li>Dendrites - receive signals from previous neurons </li></ul><ul><li>Cell body - controls/sustains neuron </li></ul><ul><li>Axon - allows nerve signals to travel along neuron </li></ul><ul><li>Terminal bodies - release neurotransmitters at tips </li></ul><ul><li>Myelin sheaths cover axon in many neurons. Protects, insulates, and speeds up conduction. </li></ul><ul><li>Myelinated neurons include “nodes of Ranvier” </li></ul><ul><li>Function … speeds up signal transmission </li></ul><ul><li>Myelinated neurons faster conductors than unmyelinated </li></ul>
  14. 14. Multipolar Neuron
  15. 15. Drugs & Neurotransmitters <ul><li>Inside of hypothalamus is our “pleasure center” </li></ul><ul><li>Motivates much of human behavior </li></ul><ul><li>Responsible for anything that gives us pleasure/joy </li></ul><ul><li>Our ability to feel good involves neurotransmitters </li></ul><ul><li>Drug use re-programs how these neurotransmitters work </li></ul>
  16. 16. Speed (Methamphetamine) <ul><li>Artificially stimulates brain to provide pleasure flush </li></ul><ul><li>When outside chemicals are introduced, brain produces less neurotransmitters </li></ul><ul><li>“ why bother?!?!?” </li></ul>
  17. 17. Cocaine <ul><li>Comes in snorted form (white powder) </li></ul><ul><li>Stimulates pleasure center then squeezes it dry </li></ul><ul><li>Hooks to dopamine transporter protein </li></ul><ul><li>So, it blocks reabsorption of dopamine </li></ul><ul><li>… ..the neurotransmitter remains in synapse and stimulates receptor cells over and over again </li></ul><ul><li>Increased heart rate, blood pressure, sexual appetite </li></ul>
  18. 18. <ul><li>As dopamine is blocked, it accumulates in synapse </li></ul><ul><li>It’s washed away </li></ul><ul><li>Brain dopamine supply becomes inadequate to maintain normal moods </li></ul><ul><li>The sending cells cannot make dopamine fast enough to make up for the loss and pleasure circuits go dry </li></ul><ul><li>Cannot experience pleasure without the drug </li></ul><ul><li>Catch-22: cocaine needed to experience pleasure, but more use = more depletion of neurotransmitter supply </li></ul><ul><li>Weight loss, trouble sleeping, mood swings, death </li></ul><ul><li>Incredibly difficult to treat </li></ul>
  19. 19. Crack <ul><li>Cheaper than cocaine </li></ul><ul><li>More potent </li></ul><ul><li>Smokable form of cocaine </li></ul><ul><li>Produces higher high and a deeper crash!! </li></ul><ul><li>Intensely addictive </li></ul>
  20. 20. Heroin <ul><li>Is a depressant </li></ul><ul><li>Far more expensive than cocaine </li></ul><ul><li>Demands higher doses to achieve the same effect </li></ul><ul><li>When addicted and going without, body goes into incapacitated nausea and convulsions </li></ul><ul><li>With an overdose, lungs fill with fluid and user drowns. </li></ul>
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