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

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