What is stimuli?

Hint: A stimuli is a detectable change in the physical or chemical structure of an organism’s internal or external environment. It is a term used in physiology and describes the ability of an organism to detect external stimuli and reaction is made.

Complete answer:
The changes that are made in an organism by the external stimuli is called sensitivity. Information is received from outside of the body like in sensory receptors work as touch receptors found in skin and light receptors inside the eyes. When a sensory receptor comes in contact with the stimuli it elicits a reflex by a stimulus transduction. External stimuli are capable of producing responses throughout the body.
Stimuli must have strength of level that exceeds the absolute threshold value in order to be detected by the stimuli. If the stimuli have less strength than absolute threshold value then the information is transmitted to the central nervous system of the body and a decision is made on how to react to the stimuli. Stimuli generally cause the body to respond but it is the central nervous system that finally determines whether a signal causes a reaction or not. There are various types of responses that occur through various types of stimuli like homeostatic imbalance, blood pressure, touch and pain, vision, smell, taste, sound, etc.

Note: There are various other types of responses that occur due to stimuli like cellular response and systemic response in our body. Systematic response includes the responses that occur in our body systems and cellular responses occur within the cell.