Senses
Your eyes, ears, nose, tongue and skin each turn a different kind of energy or chemical into nerve signals. Focus a 3D eye on near and far lamps, find your own blind spot, follow sound into the cochlea and meet the scientists who worked out how each sense works. This course is general information about how the body works. It is not medical advice.
About this course
In the 1660s Edme Mariotte, a French priest and a founding member of the Paris Academy of Sciences, showed that every eye has a place in its field of view where an object simply vanishes. He linked it to the spot where the optic nerve enters the eyeball, and the blind spot is still sometimes called Mariotte's spot. His observations started a lively debate, because it was hard to accept that everyone has a gap in their vision that nobody notices. The senses course keeps asking how we know what we know about seeing, hearing, smelling, tasting and touching.
The five sense units begin with the eye, where light crosses the cornea, the pupil and the lens before landing on the retina. Ears covers hearing and balance: three tiny bones in the middle ear pass sound on to the inner ear, and human hearing runs from about 20 to 20,000 vibrations per second. Smell and taste notes that you are born with about 10,000 taste buds, yet much of what you call taste reaches you through your nose. Touch, temperature and pain includes the Merkel cell, which picks up slow vibrations of about 5 to 15 per second. When the senses are fooled takes up a 1976 experiment, where people who heard "ba" while watching lips say "ga" reported hearing "da". It also tells how Robert Addams stared at the Falls of Foyers in 1834 and saw the rock face drift upward. The last unit adds that in 1851 Hermann von Helmholtz published a way to look through the pupil at the living retina. The 3D eye lets you move a distance slider and find your own blind spot.
Before you start
Every sense ends in a nerve signal, so Brain and nerves is useful background. The eye unit uses focusing and the ear unit uses frequencies in hertz, which Light and Waves and sound explain, though neither is required.
When you finish
You can put the cornea, pupil, lens and retina in the order light meets them, find your own blind spot, and explain what changes with presbyopia. You can describe how the middle ear bones carry sound, why food tastes bland with a stuffy nose, which receptors sense vibration and stretch, and why the McGurk effect makes people hear da.
- 1The eye and how it focusesLight crosses the cornea, the pupil and the lens before it lands on the retina, where two kinds of cells turn it into nerve signals.
- 2Ears: hearing and balanceThree tiny bones in the middle ear pass sound on to the inner ear, and human hearing covers sounds from about 20 to 20,000 vibrations per second.
- 3Smell and tasteYou are born with about 10,000 taste buds, but much of what you call the taste of food actually reaches you through your nose.
- 4Touch, temperature and painRun a fingertip over a rough surface and the skin vibrates; a receptor called a Merkel cell picks up slow vibrations of about 5 to 15 per second.
- 5When the senses are fooledIn a 1976 experiment, people who heard the syllable "ba" while watching lips say "ga" reported hearing "da".
- 6How the senses were studiedIn 1851 Hermann von Helmholtz published a way to look through the pupil at the living retina, something no one had been able to do before.
This is educational material about how the body is built and works. It is not medical advice and is not for diagnosing or treating anyone.
Sources for this course (15)
- OpenStax Anatomy and Physiology 2e, 14.1 Sensory Perception (receptors, taste, smell, hearing, balance, vision, somatosensation; openstax.org/books/anatomy-and-physiology-2e/pages/14-1-sensory-perception)
- NIH National Eye Institute "How the eyes work", "Nearsightedness (myopia)", "Farsightedness (hyperopia)", "Presbyopia" (nei.nih.gov)
- NIH NIDCD "How do we hear?", "Balance disorders", "Smell disorders", "Taste disorders" (nidcd.nih.gov)
- NobelPrize.org press releases 2004 (Axel and Buck, odorant receptors) and 2021 (Julius and Patapoutian, temperature and touch)
- facts pages 1911 (Gullstrand)
- 1961 (Békésy)
- JAMA Ophthalmology 1999 "Gullstrand, Einstein, and the Nobel Prize" (1967 and 1981 vision prizes)
- PubMed 17574069 (Mariotte and the blind spot)
- PubMed 30295065 (Helmholtz ophthalmoscope, 1851)
- PubMed 19640953 (Ikeda, umami, 1908)
- McGurk and MacDonald, Nature 264, 746 (1976)
- Addams 1834 waterfall illusion (Illusions Index; PMC5016818)
- Müller-Lyer 1889 (Wiley Encyclopedia of Cross-Cultural Psychology)
- blind spot filling-in: American Academy of Ophthalmology "Blind Spot" (aao.org) and Li et al. 2014 (PMC4103407)
- motion aftereffect as adaptation: Bach, Visual Phenomena (michaelbach.de/ot/mot-adapt)
Checked: 2026-10-17