Since simulation of the action of the human nervous system is our goal, our first step on this path is understanding how nature has solved the problem of human movement.
Simple Muscle Control
In its simplest form, we can imagine that neurons originating in the motor cortex of the human brain relay signals which contract or relax each muscle in the human body. Nature, however, first created animals with simple reflexes and then added higher systems like the motor cortex. This evolved system allows for multiple levels of motor control which simplifies the task of the highest levels of control in the motor cortex to perform more complex movements with finer control.
Simple reflexes in the nervous system simplify the task of coordinating the movement of all the muscles found in the body, as well as allow fast responses to acute events without involving the entire muscle control apparatus. Below, is an illustration of the reflex system that allows voluntary contraction of a single muscle to cause relaxation of the antagonist muscle.
This simple reflex path also serves to correct the length of a muscle when a sudden unexpected deformation occurs. This is the reflex circuit your doctor tests when he taps under your knee cap with a hammer, or when you hold out your hand and someone asks you to catch an unexpectedly heavy object.
More complex reflexes exist to provide motor control requiring contribution from multiple sense locations and affecting multiple muscles. For example, this allows the body to remain balanced as a limb is extended away from the body.
To replicate these neural control systems we have adopted a similar hierarchy in which simple reflex circuits allow complementary muscles to respond to acute events and more complex coordinated and directed movement is controlled from the high level motor control system. The end result is a highly flexible platform which will respond to physical interactions in a natural and lifelike way.