Animals with nervous systems are born with instincts. An instinct is a part of the behaviour of an organism. It is inherited (innate), not learned. However, the term does not include the operation of sense organs, and does not include the normal working of the autonomic nervous system. Instincts are to do with visible muscular action in response to releasers. Releasers are triggers which set off chains of instinctive behaviour. Although instincts are not learned, in some cases their performance can be improved by experience and practice.