DNp01 (giant fiber)
systemDescending and motor neuronsspeciesD. melanogaster3D view2 of 626 cellssources7
DNp01, the giant fiber, is a large descending neuron of the fruit fly that triggers escape. A giant fiber on each side carries looming signals from the brain to the thoracic nerve cord, where it drives the leg and wing muscles of a rapid takeoff.
| Also known as | Giant fiber · Giant fibre · GF · Giant fiber neuron |
|---|---|
| Region | Posterior brain; axon descends to the thoracic ganglion of the ventral nerve cord |
| System | Descending and motor neurons |
| In the display bundle | 2 of the 626 reconstructed neurons in the site’s MaleCNS display bundle, which shows 626 of the model’s 166,700 neurons: DNp01 2 |
What it is
In the descending neuron nomenclature, “DN” marks a descending neuron, “p” a cell body on the posterior surface of the brain and “01” its number: the giant fiber is DNp01 (Namiki et al., 2018). The giant fiber system is the neural circuit that mediates the fly’s escape response to visual stimuli (Allen et al., 2006).
Where it sits
The giant fiber innervates the LC4 optic glomerulus in the brain (Namiki et al., 2018), and its axon descends through the neck to the thoracic ganglion. There its signal is relayed to leg and wing muscle motor neurons (Allen et al., 2006; Tanouye and Wyman, 1980), including the jump muscle motor neuron (Klapoetke et al., 2017).
What it does
Faced with a looming stimulus, a fly makes either a long escape sequence that leads to stable flight or a short one that sacrifices stability for speed. The timing of a giant fiber spike relative to parallel escape circuits determines which one occurs: the giant fiber has a higher activation threshold but can override ongoing behavior to force the short takeoff (von Reyn et al., 2014).
The giant fiber sums two visual features of the approaching object: its angular expansion velocity, from LC4, and its angular size, from LPLC2 (von Reyn et al., 2017; Ache et al., 2019).