Senses and receptors: how we sense the world
Special and general senses, the kinds of receptors, taste buds and the five basic tastes, why smell matters for flavour, and why fingertips feel finer detail. With a fair test: does smell help taste?
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Scientists sort the senses into special senses, which have their own organs (vision, hearing, smell, taste and balance), and general senses spread through the body, such as touch, pain, temperature and the sense of where your body parts are (proprioception).[1]
Every sense uses receptors: cells or nerve endings that react to one kind of stimulus. Photoreceptors react to light, mechanoreceptors to pressure and vibration, thermoreceptors to heat and cold, chemoreceptors to chemicals and nociceptors to things that could harm you.[1]
You are born with about 10,000 taste buds, on the tongue, the roof of the mouth and the throat. Taste cells respond to five basic tastes: sweet, sour, bitter, salty and umami (savoury, found in broth and some cheeses). Cells for each taste are spread across the tongue, not kept in separate zones.[2]
Smell uses nerve cells high inside the nose, each with one kind of smell receptor. When you chew, smells travel up a channel from the back of your throat to your nose. Flavour is taste, smell, texture, heat and cold together, which is why food tastes bland when you have a cold.[3][2]
Touch is not equally fine everywhere. On a fingertip you can feel two points as separate when they are only about 2–3 mm apart, but on your arm they must be about 35–40 mm apart. Fingertip skin has about 100 times more receptors per square centimetre than the skin on your back.[4]
Your ears hear sounds from about 20 to 20,000 vibrations per second (20–20,000 Hz). Deep inside each ear, balance organs sense the position of your head and when it turns.[1]
Try it: Does smell help taste?
You need
- Small peeled pieces of apple and pear, all the same size, cut by the teacher (only if school rules and allergies allow)
- A clean plate and napkin for each taster
- A glass of water for each taster
- Results table
Safety
Check food allergies and school food rules with parents first; anyone may sit out or swap to the tester role. Wash hands, use clean plates, one taster per plate and no sharing. The teacher does all the cutting. Keep eyes closed only while sitting still.
What to do
- Question: can you tell apple from pear just as well with your nose pinched? Write a prediction.
- Work in pairs: a taster and a tester. The taster closes their eyes.
- Nose pinched: the tester gives 6 pieces in a random order (3 apple, 3 pear). The taster chews each and says 'apple' or 'pear'. Sip water between pieces. Record right or wrong.
- Nose open: repeat with another 6 pieces in a new random order.
- Fair test: same size pieces, same fruit, same number of tries, eyes closed both times. Only the nose changes. Count the right answers in each condition and compare with the class.
What happens, and why?
Apple and pear are both sweet, so the taste buds alone give similar messages. Much of what makes them different is their smell. When you chew, the smell travels from the back of the throat up to the nose; pinching your nose blocks that route, so the flavour is weaker and guessing is harder.[3][2]
Play: Which receptor?
Which kind of receptor mainly detects each stimulus?
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Quiz
Other ages: Ages 6–7 · Ages 15–16