Our body has some reflexes. One reflex commonly used by doctors is the so-called patellar reflex. This reflex is an example of how fast a direct connection between a motor and sensory nerve can be. As soon as someone (for example, a doctor) taps the tendon of the quadriceps (muscle at the front of the thigh), the so-called muscle spindle in that muscle is stretched. The sensory nerve passes this signal directly to the motor nerve. The motor nerve then immediately responds by bringing the quadriceps back to its original (resting) position.
Author: Caroline Benjamins (translated by Melanie Smekal)