Neurons

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Neurons Neuroanatomy

• What are the characteristics of neurons important
  for Cognitive Neuroscience?
• What is the brain structure important for
  CogNeuro?

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Classes of neurons

• Unipolar - One process extends from body, which
  can contain both dendrites and axon terminals
• Bipolar - One axon and one dendrite process.
• Multipolar - Many dendrite processes.
• Pseudounipolar - Bipolar cells where the dendrite
  and axon processes have merged.
• Well be primarily interested in multipolar cells.

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Neural membrane

• There are specialized structures in the neural
  membrane that allow various elements to cross in
  and out of the cell
• Ion channels Proteins that cross the cell wall,
  creating pores that allow ions (Na, K, Cl-) to
  pass.
• Specific to particular ions more K channels
• Nongated and gated
• Ion pumps Actively transport ions across the
  membrane, creating an electric gradient across
  the membrane (3 Na out 2 K in)

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Cellular currents

• There are two types of electrical currents that
  can pass through a neuron
• Active currents are ones that are caused by
  explicit chemical activity (opening and closing
  of ion channels) ex - at the synapse and across
  the surface of the axon
• Passive currents are ones that simply pass
  through the cytoplasm, typically as a response to
  active currents ex - within the cell body as a
  result of synaptic activity within the axon as a
  result of action potentials.

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Action Potential

• The signal a neuron generates down its axon is
  called an action potential.
• All action potentials are the same magnitude
  (strength), so they are either on or off.
• An action potential is only generated if the
  depolarization of the cell membrane crosses a
  threshold.
• We determine how excited a neuron is by its
  firing rate - how many action potentials per
  second it generates.

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Depolarization of the AP

• As opposed to the nongated ion channels discussed
  so far, action potentials are driven by gated
  channels that open in response to high voltage
  levels (the threshold).
• In particular, gated Na channels are opened by
  membrane depolarization, which allows Na into
  the cell. This causes further depolarization,
  which opens more channels..

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Repolarization of the AP

• Depolarization also causes voltage-gated K
  channels to open, but slightly after the Na
  channels. This drives K out of the cell,
  reestablishing the resting potential of the cell
  this is called repolarization.
• Because of the delay, K flows out after Na
  stops flowing in, so there is a brief period of
  hyperpolarization

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Neurotransmitter

• Neurons communicate by sending chemical messages
  called neurotransmitters to other neurons.
• These neurotransmitters travel from axon to
  either the dendrite or the cell body across the
  synapse.
• Where a synapse is depends on what the connection
  type is
• Excitatory Axon to dendrite
• Inhibitory Axon to cell body

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