Inhibitory and Excitatory Signals

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Inhibitory and Excitatory Signals
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Excitatory Potentials

• Excitatory postsynaptic potential (EPSP) occurs
  when membrane potential goes toward threshold
  (becomes more depolarized).
• ACh and Glutamate gated ion channels are
  excitatory.
• Typically, these neurotransmitter-gated channels
  are permeable to sodium (Na) and potassium (K).

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Inhibitory Potentials

• Inhibitory postsynaptic potential (IPSP) occurs
  when membrane potential goes toward threshold
  (becomes more depolarized).
• GABA and Glycine gated ion channels are
  inhibitory.
• Typically, an inhibitory neurotransmitter-gated
  channel is permeable to an anion such as chloride
  (Cl-).

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Synaptic Integration

• An individual synapse, by itself, cannot generate
  an action potential in a receiving neuron.
• Many EPSPs add together to produce enough
  depolarization to cross the threshold and
  generate an action potential
• Two kinds of summation
• Spatial
• Temporal

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Shunting Inhibition

• Dendritic length constant determines how far
  along the dendrite an excitatory current will
  travel.
• Inhibitory synapses located at the soma can
  prevent an EPSP from reaching the axon hillock.
• Inhibitory input occurs only when the inhibitory
  neuron has an action potential and releases
  neurotransmitter to inhibitory ion channels.

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Kinds of Receptors

• All neurotransmitters bind and act at more than
  one kind of receptor.
• Two main kinds of receptors
• Ion channel receptors
• G-protein-coupled receptors

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G-Protein-Coupled Receptors

• Change the excitability of the neuron in two
  ways
• Change calcium ion levels (releasing
  neurotransmitter).
• Activate intra-cellular second messengers
• Signal amplification
• Signaling at a distance
• Cascades of activation
• Long-lasting chemical changes in neuron

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Phosphorylation

• Addition of a phosphate group to the protein of
  an ion channel can change its functioning making
  it more or less likely to open.
• This process is called phosphorylation.
• Removal of the phosphate group by a protein
  phosphatase is called dephosphorylation.
• This process results in modulation of the
  excitability of neurons.

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Importance of Calcium

• Voltage-gated calcium (Ca2) channels permit CA to
  enter the cell.
• As Ca2 rises, it binds with the neuron,
  preventing additional calcium from entering.
• Increased calcium concentrations can cause
  dephosphorylation or permanent inactivation of a
  channel.
• Calcium signals neurotransmitter release.