Stimulus (physiology)

<p>In <a href="/facts/Physiology/fh25y2pQ">physiology</a>, a stimulus is a change in a <a href="/facts/Organism/j8JkL09u">living thing's</a> internal or external <a href="/facts/Environment_(systems)/lmzo8gh1">environment</a>. This change can be <a href="/facts/Sense/cB7rTqYF">detected</a> by an organism or organ using sensitivity, and leads to a physiological reaction. <a href="/facts/Sensory_receptor/EwY1m2bV">Sensory receptors</a> can receive stimuli from outside the body, as in <a href="/facts/Somatosensory_system/0nhRsBnt">touch receptors</a> found in the skin or light receptors in the eye, as well as from inside the body, as in <a href="/facts/Chemoreceptors/KC6IDxzf">chemoreceptors</a> and <a href="/facts/Mechanoreceptors/rj6j4Nt3">mechanoreceptors</a>. When a stimulus is detected by a sensory receptor, it can elicit a <a href="/facts/Reflex_action/codE8Eff">reflex</a> via <a href="/facts/Transduction_(physiology)/r9ce5wG9">stimulus transduction</a>. An internal stimulus is often the first component of a <a href="/facts/Homeostasis/rloTGAHa">homeostatic control system</a>. External stimuli are capable of producing systemic responses throughout the body, as in the <a href="/facts/Fight-or-flight_response/hRrBawJP">fight-or-flight response</a>. In order for a stimulus to be detected with high probability, its level of strength must exceed the <a href="/facts/Absolute_threshold/3PMAc0vt">absolute threshold</a>; if a signal does reach threshold, the information is transmitted to the <a href="/facts/Central_nervous_system/k8I6To97">central nervous system</a> (CNS), where it is integrated and a decision on how to react is made. Although stimuli commonly cause the body to respond, it is the CNS that finally determines whether a signal causes a reaction or not.
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Stimulus (physiology) open-in-new

Stimulus (physiology)