Neuronal Circuitry

Spatial summation
The postsynaptic neuron adds together the simultaneous firings of its presynaptic neurons until threshold. The axon hillock of the postsynaptic neuron then generates the action potential.

Temporal summation
The postsynaptic neuron receives rapid and frequent action potentials from few presynaptic neurons. Excited neurons have a greater effect on the postsynaptic neuron, causing the axon hillock to generate an action potential.

Neurotransmitters
Neurotransmitters that depolarize the postsynaptic neuron cause excitatory postsynaptic potentials (EPSPs). Neurotransmitters that inhibit the neuron from firing cause inhibitory postsynaptic potentials (IPSPs).

Acetylcholine, norepinephrine and glutamate are mostly excitatory. Dopamine, gamma-aminobutyric acid (GABA), glycine and serotonin are mostly inhibitory.

Neuronal circuitry

1. Convergence: a neuron takes in multiple inputs. 
2. Divergence: a neuron outputs to multiple cells. 
3. Negative feedback: neuron A stimulates neuron B that inhibits the outputs of neuron A. 
4. Lateral inhibition: a neuron stimulates its postsynaptic neurons, which send inhibitory signals and only a few excitatory signals. This limits neural impulses to a narrow path. 
5. Reverberation: a positive feedback circuit to sustain firing along a neural pathway.