• 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