reflex action

an unconscious movement that is brought about by relatively simple nervous circuits in the CENTRAL NERVOUS SYSTEM . In its simplest form it involves a single reflex are of one RECEPTOR and SENSORY nerve, which forms a SYNAPSE in the BRAIN or SPINAL CORD with a MOTOR NERVE , which then transmits the impulse to a MUSCLE or GLAND to bring about a response. However some reflex actions are more complicated than this, involving several NEURONS . Examples are the planter reflex of the toes when the sole of the foot is stroked, the knee-jerk reflex and the reflex PUPIL of th EYE , which contracts suddenly when a light is directed on its surface. The presence or absence of reflexes gives an indication of the condition of the nervous system and is a pointer to the presence or absence of disease or damage.