The metathoracic ganglion contains thousands of neurons, and probably many hundreds of these are involved in jumping. However, I am going to concentrate on just 4 neuron types (on one side - there are equivalent neurons on the other), which cover the most important bits of the motor programme.
The cartoon below shows the activity of these four neuron types in relation to the movement of the leg. The four traces are graphs of the membrane potential of the neurons (vertical axis), plotted against time (horizontal axis). The graphs show synaptic potentials (small lumps and bumps) and nerve impulses (the spike-like potentials).
The key points in interpreting these records are:
Science stuff: more on neurons and recording their activity
These records confirm the story I have been telling. The first thing that happens is that flexor excitor motorneurons are activated, causing the initial flexion. Next, the flexor and extensor excitor motorneurons are active together. The flexor muscle holds the tibia flexed using the mechanical system described previously, while tension builds up in the extensor muscle and energy is stored in the cuticle springs. This constitutes the co-contraction phase. During this, the M neuron is inhibited (dashed line). Finally, the M interneuron and the flexor inhibitor produce a burst of spikes. The M interneuron shuts down the flexor excitor motorneurons within the ganglion, so the flexor muscle is no longer activated, while the flexor inhibitor motorneurons speed up the relaxation of the flexor muscle. The end result is that the flexor muscle looses tension very rapidly and the leg extends with an explosive release of energy.