Editing Somatic nervous system (section)

===Reflex arcs===
A [[reflex arc]] is a [[neural circuit]] that creates a more or less automatic link between a sensory input and a specific motor output.  Reflex circuits vary in complexity—the simplest spinal reflexes are mediated by a two-element chain, of which in the human body there is only one, also called a monosynaptic reflex (there is only one synapse between the two neurones taking part in the arc: sensory and motor). The singular example of a monosynaptic reflex is the [[patellar reflex]]. The next simplest reflex arc is a three-element chain, beginning with sensory neurons, which activate [[interneuron]]s inside of the spinal cord, which then activate motor neurons.  Some reflex responses, such as withdrawing the hand after touching a hot surface, are protective, but others, such as the patellar reflex ("knee jerk") activated by tapping the patellar tendon, contribute to ordinary behavior.