Descending neurons
systemDescending and motor neuronsspeciesD. melanogaster3D view29 of 626 cellssources5
Descending neurons carry signals from the fruit fly’s brain through the neck to the ventral nerve cord, where the circuits for the legs and wings are. Complete connectomes count about 1,300 of them.
| Also known as | DNs · Descending interneurons |
|---|---|
| Region | Brain to ventral nerve cord, through the neck connective |
| System | Descending and motor neurons |
| In the display bundle | 29 of the 626 reconstructed neurons in the site’s MaleCNS display bundle, which shows 626 of the model’s 166,700 neurons: DNa02 2, DNa11 1, DNb02 1, DNb03 1, DNd03 1, DNg03 1, DNg05_b 1, DNg07 1, DNg12_a 1, DNg23 1, DNg100 2, DNg106 1, DNg109 1, DNge019 1, DNge041 1, DNge093 1, DNge115 1, DNge121 1, DNge125 1, DNp01 2, DNp32 1, DNp33 1, DNp46 1, DNp66 1, DNpe015 1, DNpe039 1 |
What they are
In most animals the brain controls the body through descending neurons that traverse the neck, and their activity activates, maintains or modulates locomotion and other behaviors (Namiki et al., 2018). A light-microscopy survey estimated about 350 on each side of the fly brain (Namiki et al., 2018); electron-microscopy reconstructions later found 1,315 to 1,347 across three datasets, almost twice the earlier estimate (Stürner et al., 2025).
Names
Names follow a scheme introduced in 2018: “DN”, then a letter for the position of the cell body (a, anterior dorsal; b, anterior ventral; c, pars intercerebralis; d, outside the anterior cluster; g, gnathal ganglion; p, posterior surface of the brain; x, outside the brain), then a number (Namiki et al., 2018). Cell types in the MaleCNS follow and extend this scheme.
Organization
Their targets in the nerve cord form a layered system that reflects two largely independent means of locomotion, walking and flight (Namiki et al., 2018). In the male nerve cord connectome, direct connections from descending neurons onto motor neurons are infrequent (Cheong et al., 2026). Command-like descending neurons directly recruit networks of other descending neurons to orchestrate behaviors that involve many body parts (Braun et al., 2024).
Behavior
Optogenetic activation of individual descending neuron types in freely moving flies drove stereotyped behaviors for most types; several types evoked similar behaviors, and the result often depended on what the fly was doing beforehand (Cande et al., 2018). Well-studied examples include the giant fiber, DNp01, which triggers escape takeoff, and DNa02, which shortens the strides on the inside of a turn.