Synaptic transmission


Electrical Synapses

  • Synapses connect neurons to form large circuits, there are 10^15 neurons
  • They can undergo two types of changes:
  •                    Short term - Used for signalling
  •                    Long term - Used for learning and memory

Electrical synapses

  • This is a type of synapse where the current flows from one neuron to another through a gap junction.
  • The membranes are only 3.5 nanometers apart.
  • They are comprised of two hemi-channels called connexons.
  •            Connexons have six subunits called connexins.
  •            A connexin has four membrane spanning domains.
  • They allow for faithful transmission/high speed transmission and bidirectional signalling, but they have limited flexibility as they are faithful conveyors of signal.
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Chemical synapses

  • Otto Loewi showed the importance of chemical synapses by taking synaptic fluid from a frog vagua nerve and putting it into a recipient heart; the fluid caused the heart rate to slow.

The Nicotinic acetylcholine receptor

  • It has 2 alpha, 1 beta and 1 gamma subunit.
  • A twisting response upon acetylcholine binding opens the channel.
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Post synaptic responses

  • A postsynaptic depolarisaion is called an excitatory postsynaptic potential (EPSP).
  • In muscle, the same thing is called an end plate potential
  • We know that the two major players are Na and K through studying the reversal potential.
  •                    You can determine this by recording the post synaptic potential against a control                         membrane potential
  •                    You start at -70mV and evoke a response and then increase the potential                                   stepwise; the point at which no ion flow occurs is the reversal potential.
  • In inhibitory synapses, the result of stimulation is hyperpolarisation, which called an inhibitory postsynaptic potential (IPSP).
  • There may also be an influx of Cl-.
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