A reflex action is a type of innate behavior and an involuntary and rapid response to a stimulus, or cue.
One example of a human reflex action is the knee-jerk reflex. To test this reflex, a doctor taps the tendon below your kneecap with a rubber hammer. The tap activates nearby neurons, causing your lower leg to kick involuntarily. This automatic response depends on circuits of neurons that run between the knee and the spinal cord (without involving the brain).
Some reflexes are present in human babies abut are lost or placed under conscious control as the baby grows older. For instance, a newborn baby will suck at anything that touches the roof of its mouth. This reflex helps the baby get food by ensuring it will such at its mother’s breast or a bottle placed in its mouth.