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