A receptor detects a stimulus. An effector carries out the response. One starts the pathway and the other finishes it.
This lesson is part of Body coordination in SPM Science. Names follow your Science textbook.
How do I tell them apart?
Ask two questions about any named structure. Does it detect a change, or does it act? Does it sit at the start of the pathway, or at the end?
Receptors receive the change. Effectors produce the effect. The link between them is a signal carried by nerves or by the blood.
Worked example: four original situations
Fill in the stimulus, receptor and effector for each.
| Situation | Stimulus | Receptor | Effector | Response |
|---|---|---|---|---|
| Bright light shines in the eye | Bright light | Light-sensitive cells in the eye | Muscle in the iris | Pupil becomes smaller |
| A sharp object pricks the finger | Sharp object | Pain receptors in skin | Muscle in the arm | Hand pulls away |
| A smell of food reaches the nose | Smell | Smell receptors in the nose | Gland in the mouth | Saliva is released |
| A cold wind blows on the skin | Cold | Temperature receptors in skin | Muscles under the skin | Shivering begins |
Take the first row. The light-sensitive cells detect the light, which makes them the receptor. The iris muscle changes the pupil, which makes it the effector. The link between them is a signal, not a third name to add.
The mistake: swapping the two
A common slip is to name the muscle as the receptor because the muscle is the part that moves. The word “receptor” refers to detecting, not to moving.
| Question | Wrong | Right |
|---|---|---|
| Which part detects the light? | The iris muscle | Light-sensitive cells in the eye |
| Which part acts? | The eye | The iris muscle |
If the question says “detect”, answer with a receptor. If it says “respond” or “act”, answer with an effector.
Writing a full explanation
A full answer gives the stimulus, the receptor, the signal and the effector, in that order. Use short sentences and keep the order.
Example: “Bright light is the stimulus. Light-sensitive cells in the eye detect it and send a signal. The iris muscle responds by making the pupil smaller.” The signal route is covered in tracing a simple response pathway.
Check yourself
Name the stimulus, receptor and effector when a student smells hot food and their mouth waters.
Answer
Stimulus: the smell of food. Receptor: smell receptors in the nose. Effector: a gland in the mouth. Response: saliva is released.
Check that the receptor detects and the effector acts. If you named the mouth as a receptor, go back to the rule: receptors detect, effectors act.
What to study next
Move on to interpreting curriculum scenarios without diagnosing symptoms. For a comparison of the two systems, see comparing nervous and hormonal coordination.
For a teacher to test you on new stimuli, see online one-to-one Science tuition.