Topic 14.2 · Core
Sense Organs and Receptors
A nervous response has to begin somewhere, and that somewhere is a sense organ. This page covers what a sense organ actually is before the chapter narrows in on the one Cambridge studies in detail — the eye.
What a sense organ is
A sense organ is a group of receptor cells that respond to specific stimuli.The word “specific” is doing real work in that definition: a given sense organ, or receptor group, only ever responds to its own particular stimulus, never to stimuli in general. A structure built to detect light doesn’t also detect sound just because it’s classed as a sense organ — specificity is part of what the definition requires, not an incidental detail.
The required stimulus categories
For this syllabus point, the stimuli a sense organ can be built around are:
- light
- sound
- touch
- temperature
- chemicals
Receptors detect these stimuli; producing the actual response is a separate job that belongs to an effector, further along the pathway. Keeping receptor and effector apart matters more than it might first seem — they are different structures doing different jobs at opposite ends of a nervous pathway, and an answer that blurs the two together is describing a step that doesn’t actually exist.
Why the eye gets its own page
Cambridge singles out one sense organ for detailed study: the eye, which detects light and forms the starting point of a nervous pathway to the brain. Because the eye carries so much required structural and mechanistic detail — the named parts, the pupil reflex, accommodation, and the distinction between rods and cones — it has a full page of its own rather than being folded into this general overview. See the eye for the complete treatment.
Everything a receptor detects still has to be carried somewhere and coordinated. That’s the job of the nervous system, which this page’s definition connects directly into: a stimulus reaches a receptor here, and from there travels along the pathway covered on the reflex arc page.