How fast is a fly’s reaction time?
A fly’s fastest escape jump starts a few hundredths of a second after danger looms. A person needs about a quarter of a second just to react.
When something looms toward a fly, the signal runs from its eyes to its leg muscles in tens of milliseconds. A millisecond is a thousandth of a second. In the WiredMind lesson, the jump neurons fire about 30 ms after the swatter appears. That figure comes from a simple model, not from a recording of a fly, but it is the right order of size. A person takes around 250 ms just to react to a flash of light.
The speed comes from the wiring. The path is short: looming neurons, then the giant fiber, then the jump neurons. The giant fiber is unusually thick, which makes its signal travel fast. And in a real fly it hands the signal on through electrical synapses, direct channels between cells with almost no delay.
See it in a lesson
Key terms
- Giant fiber
- A very thick nerve cell that runs from the brain down into the nerve cord. It carries the fly’s fastest escape signal. A fly has two, one on each side.
- Electrical synapse
- A direct channel between two neurons that passes a signal with almost no delay. The map behind the lessons records chemical synapses only.
- Motor neuron
- A neuron that carries a command out to a muscle and makes it contract.
- Action potential (spike)
- A brief electrical pulse that an active neuron sends along its length, also called a spike or an action potential. In the lessons, each flash of light marks one.