NE

Nervous System

  • Nervous System Cell

    • Neuron
    • Nerve cell
    • Structure fits function
    • Many entry points for signal
    • One path out
    • Transmits signal

  • Fun Facts about Neurons

    • Most specialized cell in animals
    • Longest cell
    • Blue whale neuron
      • 10–30 meters long
    • Giraffe axon
      • 5 meters long
    • Human neuron
      • 1–2 meters long

  • Transmission of a Signal

    • Start the signal
    • Trigger the signal
    • Propagate the signal
    • Re-set the system

  • Transmission of a nerve signal

    • Neuron has a similar system
    • Protein channels are set up
    • Once the first one is opened, the rest open in succession
      • All or nothing response
    • A “wave” action travels along the neuron
    • Have to reset channel, so the neuron can react again

  • Cells Surrounded by Charged Ions

    • Cells live in a sea of charged ions
    • Anions (negative)
      • More concentrated within a cell
      • Cl-, charged amino acids
    • Cations (positive)
      • More concentrated in the extracellular fluid
      • Na+

  • Cells have Voltage

    • Opposite charges on opposite sides of the cell membrane
    • Membrane is polarized
      • Negative inside; positive outside
      • Charge gradient
      • Stored energy

  • How Does a Nerve Impulse Travel

    • Stimulus: nerve is stimulated
    • Reaches threshold potential
      • Opens Na+ channels in cell membrane
      • Na+ ions diffuse into cell
    • Charges reverse at that point on neuron
      • Positive inside; negative outside
      • Cell becomes depolarized
    • Wave: nerve impulse travels down neurons
    • Change in charge opens next Na+ gates down the line
      • “Voltage-gated” channels
    • Na+ ions continue to diffuse into the cell
    • “Wave” move down neuron
      • Action potential
    • Reset: 2nd wave travels down neuron
    • K+ channels open
      • K+ channels open up more slowly than Na+ channels
    • K+ ions diffuse out of the cell
    • Charges reverse back at that point
      • Negative inside; positive outside
    • Combined waves travel down neuron
    • Wave of opening ion channels moves down neuron
    • Signal moves in one direction
      • Flow of K+ out of cells stops activation of Na+ channels in the wrong direction
    • Action potential propagates
    • Wave
      • Nerve impulse or action potential
    • Brain to fingertips in milliseconds

  • Voltage-gated channels

    • Ion channels open and close in response to changes in charge across membrane
    • Na+ channels open quickly in response to depolarization and close slowly
    • K+ channels open slowly in response to depolarization and close slowly

  • How does the nerve reset itself

    • After firing, a neuron has to reset itself
    • Na+ needs to move back out
    • K+ needs to move back in
    • Both are moving against concentration gradients
      • Need a pump
    • Sodium-Potassium Pump
    • Active transport protein in membrane
      • Requires ATP
    • 3 Na+ pumped out
    • 2 K+ pumped in
    • Resets charge across membrane

  • Action Potential Graph

  • Myelin Sheath

    • Axon coated with Schwann cells
    • Insulates axon
    • Speeds up signal
      • Signal hops from node to node
      • Saltatory conduction
    • 150 m/sec vs. 5 m/sec

  • Chemical synapse

    • Events at synapse
    • Action potential depolarizes membrane
    • Opens Ca+ channels
    • Neurotransmitter vesicles fuse with membrane
    • Release neurotransmitter to synapse
    • Neurotransmitter binds with protein receptor
      • Ion-gated channels open
    • Neurotransmitter degraded or reabsorbed

  • Nerve impulse in next neuron

    • Posy-synaptic neuron
    • Triggers nerve impulse in next nerve cell
      • Chemical signal opens ion-gated channels
      • Na+ diffuses into cell
      • K+ diffuses out of cell
      • Switch back to voltage-gated channels

  • Neurotransmitters

    • Acetylcholine
    • Transmit signal to skeletal muscle
    • Epinephrine (adrenaline) and norepinephrine
    • Fight or flight response
    • Dopamine
    • Widespread in brain
    • Affects sleep, mood, attention, and learning
    • Lack of dopamine in brain, associated with Parkinson’s disease
    • Excessive dopamine is linked with schizophrenia
    • Serotonin
    • Widespread in brain
    • Affects sleep, mood, attention, and learning
    • Weak point of nervous system
    • Any substance that affects neurotransmitters or mimics them affects nerve function
      • Gases
      • Nitrous oxide
      • Carbon monoxide
      • Mood altering drugs
      • Stimulants

Amphetamines

Caffeine

Nicotine

  • Depressants

Quaalude

Barbiturates

  • Hallucinogenic drugs
    • LSD
    • Peyote
    • SSRI
    • Prozac
    • Zoloft
    • Paxil
    • Poisons
    • Acetylcholinesterase
    • Enzyme which breaks down acetylcholine neurotransmitter
      • Acetylcholinesterase inhibitors are neurotoxins
      • Snake venom
      • Sarin
      • insecticides