Introduction

Irritability (sensitivity) – is the ability to detect and respond to changes in the environment.

Stimulus- is changes in the environment (variation in conditions which can produce a change in activity of part or the whole organism).

Response –is the change in activity by the organism.

Receptor – body part that receive stimuli.

Effector – body part that bring about response.

Co-ordination – the linking of all activities that takes place from detection of a stimulus to the response by the organism.

In order for sensitivity and response to be effected there must be

• receptors to receive the stimuli,
• coordinator to integrate information received,
• transmission systems to conduct the stimuli
• effectors to respond to the stimuli.

Animals, unlike plants, have two different but related systems of co-ordination, the nervous system and the endocrine system.