Chemical Synapses

• Chemical synapses are uni directional with a pre-synaptic neuron sending chemicals over to the post-synaptic neuron.
• These are neurotransmitters, and they cross a bit of space called the synaptic gap.
• There are a lot of different neuro transmitters, and it's not entirely clear how all behave.
• However, we typically model this as current being sent to the post-synaptic neuron.
• Depending on the type of neurotransmitter (and in some case type of post-synaptic neuron) the activation of the post-synaptic neuron increases or decreases.
• If the synapse is static, it always sends the same amount of activation.
• The activation isn't typically sent all at once, but is spread over time.
• Different types of models have an alpha transfer (a bump up that declines) or exponentially declining transfer.
• In Nest you can typically pick the type of transfer, and you can set parameters (for example for time of transfer).
• Note that the activation is typically not transferred during the post-synaptic neuron's refractory period. It's just lost.