Diagram of the neural system’s response and processing of external signals (using the olfactory neural system of Drosophila as an example). Black text represents names of neuron, while brown uppercase letters represent structures in the Drosophila brain. OSN, olfactory sensory neuron; LN, local neuron; PN, projection neuron; AL, antennal lobe; LH, lateral horn; MB, mushroom body.