The Nervous System

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The Nervous System
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Peripheral Nervous System
Sympathetic system prepares body for stress or
action triggers fight or flight reactions
Parasympathetic system returns body systems to
normal, lowers heart breathing rates, promotes
digestion
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The Neuron A Powerful Computer

• Neurons
• Sensory neurons
• Motor neurons
• Interneurons
• Glial cells

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Reflexes
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The Neuron
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Major Parts of a Neuron
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The Neuron A Powerful Computer

• Neural impulses The brain in action
• Ions
• Action potential
• All-or-none law
• Myelin

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Ion Flow that Produces an Action Potential
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Neural Firing

• A resting neuron is negatively charged
• If a portion is stimulated beyond its threshold,
  it briefly reverses polarity
• This polarity reversal travels down the neuron
• Neurotransmitters are released at the axon
  terminals

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Synapse

• Tiny gap between an axon terminal another
  neuron (or specialized cell).
• Firing neurons release neurotransmitters that
  cross the synapse.

• Synaptic Vesicles
• Hold the neurotransmitter.
• Neural firing drives them to the synapse, where
  they release their chemicals.

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Synapse

• The neurotransmitter binds to the receptor site
  on the target cell
• Ion gates open
• Excess neurotransmitter is reuptaken

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Neurotransmitters

• After crossing the synapse, the neurotransmitter
  is reuptaken or degraded
• There are more than 40 known types
• Different neurotransmitters have different
  effects
• Drugs, neural diseases often affect
  neurotransmitters

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Neurotransmitters

• Acetylcholine important for learning, memory,
  muscle movement
• Serotonin influences mood and regulates food
  intake
• Dopamine important to movement and to frontal
  lobe activity
• GABA important in inhibiting neural activity
• Norepinephrine maintains alertness wakefulness
• Endorphins regulate firing of pain neurons

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Drugs

• Many drugs influence synaptic transmission
• Drugs can be agonistic or antagonistic

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Agonistic Drugs

• Increase synthesis of neurotransmitter, or
• Increase release of neurotransmitter, or
• Activate receptors, imitate neurotransmitter, or
• Inhibit reuptake of neurotransmitter

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Antagonistic Drugs

• Interfere with release of neurotransmitter, or
• Occupy and block neurotransmitter sites, or
• Cause neurotransmitter loss from vesicles.

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Psychology and Neurons

• Tying human behavior to neurons is difficult.
• There may be 100 billion neurons in your body.
• Each neuron has many connections.