C. elegens Sensory Networks

Tickle a C. elegens on its side with the tip of an eyelash and it will wiggle away from the touch. A stimulus (touch with an eyelash) activates a touch neural network in the worm that results in a physical response (movement away from the stimulus). And the whole process requires exactly and only three neural cells: (1) a sensory neural cell, (2) an interneuron cell and (3) a motor neural cell.. 

As seen in the image below, C.elegens has only 6 touch sensory cells in its body: (a) two ALM - anterior lateral touch (b) two PLM - posterior lateral touch (c) one AVM - anterior ventral touch and (d) one PLM posterior ventral touch.  As seen in the diagram above, each of these is attached to an interneuron cell  which is connected to a motor neuron cell. The motor neuron cell is connected to a muscle cell which produces movent when it receives a signal from the motor neuron.

So far the response to a touch stimulus in straightforward. But C. elegens (as well as humans) are simultaneously affected by chemicals in their bodies which modulate.effects of the sensor neuron and interneuron. That is, the neural system of C. elegens (as well as humans) is neurons in a sea of chemical -- neuromodulaors --  that surround them.These chemical are octopamine, tyramine, dopamine, serotonin,  at least 250 distinct neuropeptides

 Octopamine is the worm version of norepinephine in vertibrates.which signals stress in such things as fight or flight responses. Tyramine (also found in humans) plays a role in behavioral and motor functions. Dopamine (also found in humans) propels an individual's behavior towards or away from ("like" or "dislike") various stimuli. Serotonin (also found in humans) is involve in cognition, reward, learning (yes C. elegens can learn), memory (yes, C. elegens can remember) , and numerous physiological processes largely associated with the gastrointestinal tract.

Additionally, sensory neurons can pass information between each other. Interneurons can do the same. And, interneurons in one neural cell can pass information backwards to sensory neutrons in other neural cells.  

And so it is that neurons in a sea of neuromodulators control not only movement in both C. elegens and humans but all functions in them. The worm wiggles away from danger and humans run away from danger.