Synapses and Neural Pathways

How do we measure communication between neurons?
1. Electrically: neurophysiology
  1. Branch of physiology that deals with the flow of ions
  2. Electroencephalogram (EEG)
    1. Advantages
      1. Non-invasive
      2. High temporal resolution
    2. Disadvantages
      1. Low spatial resolution
      2. Only record from cortex
  3. Multiple unit recording
    1. Records brain rhythms
    2. Synchronous firing produces measurable waves of activity
    3. Advantages
      1. Average spatial resolution
      2. Average temporal resolution
    4. Disadvantages
      1. Only records groups of neurons
      2. Invasive - mostly used on animals
  4. Single unit extracellular
    1. Advantages
      1. Very high spatial resolution (multiple single neurons)
      2. High temporal resolution (action potentials)
    2. Disadvantages
      1. Invasive
      2. No knowledge of intracellular events
  5. Intracellular
    1. Advantages
      1. Very high spatial resolution
      2. Examine sub-cellular processes
    2. Disadvantages
      1. Fragile electrodes
      2. One cell at a time
      3. Only in anaesthetised animals
2. Chemically: microdialysis
  1. Invasive procedure
  2. Slow - sample every few minutes
Communication between neurons
1. Frequency is important, not size
  1. If the stimulus is weak, only a few action potentials will be fired.
2. Spike timing
  1. Rhythms occur when a lot of neurons fire action potentials at the same time.
  2. Timing of an action potential relative to a rhythm can change the information it carries
3. Neurotransmitters work on post-synaptic receptors on dendrites
  1. Ionotropic receptors
    1. Transmit info quickly
    2. Simple mechanism
  2. Metabotropic receptors
    1. Slow-acting and long lasting
    2. Complex mechanism
4. Two types of neurotransmitter
  1. Excitatory
    1. Causes depolarisation
    2. Glutamate
  2. Inhibitory
    1. Causes hyperpolarisation; stops action potentials from being generated
    2. GABA
  3. Excitation/inhibition caused by open ion channels
    1. Four types
5. Autoreceptors
  1. Bind to neurotransmitters released by the neuron on which they are situated
  2. Can be anywhere on cell membrane; usually inhibitory; help self-regulate neurons

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Synapses and Neural Pathways

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