Unconditioned and conditioned reflexes

Higher nervous activity is the work of the cerebral cortex and ensures behaviour adapted to the outside world in humans and animals. Its reflex basis was revealed by the Russian scientists I. M. Sechenov (“Reflexes of the Brain”, 1863) and I. P. Pavlov; Pavlov distinguished unconditioned and conditioned reflexes. Unconditioned reflexes are inborn, inherited, almost unchanged through life and the same in all members of a species; the cortex is not required, and the arc passes through the brain stem and spinal cord. They include feeding (salivation, an infant’s sucking), defensive (sneezing, coughing, blinking, pulling a hand away), orienting (turning to an unfamiliar sound) and reproductive reflexes. A newborn’s first breath is also an inborn reflex: carbon dioxide rises in the blood and stimulates the breathing centre in the medulla. A complex chain of inborn behaviour is called instinct. Unconditioned reflexes help keep the internal environment constant but are not enough when conditions change; so conditioned reflexes form during life as well.