Receptor types by stimulus
6 rows| Type | Detects | Examples |
|---|---|---|
| Mechanoreceptor | Physical deformation | Touch, pressure, hearing, balance, stretch, blood pressure |
| Chemoreceptor | Dissolved molecules | Taste, smell, blood O₂/CO₂/pH |
| Thermoreceptor | Temperature | Warm and cold free nerve endings; snake pit organs |
| Photoreceptor | Light | Rods and cones; eyespots; ommatidia |
| Electroreceptor | Electric fields | Ampullae of Lorenzini in sharks |
| Nociceptor | Tissue damage | Pain — free nerve endings, tonic (slow-adapting) |
Skin mechanoreceptors
5 rows| Receptor | Depth | Adapts | Senses |
|---|---|---|---|
| Meissner corpuscle | Shallow | Fast | Light touch, fine texture |
| Merkel cell | Shallow | Slow | Sustained touch, edges, shape |
| Pacinian corpuscle | Deep | Very fast | Deep pressure, vibration |
| Ruffini ending | Deep | Slow | Skin stretch, sustained pressure |
| Free nerve ending | Shallow | Slow (tonic) | Pain and temperature |
Rods vs cones
5 rows| Feature | Rods | Cones |
|---|---|---|
| Number per eye | ~100–120 million | ~3 million |
| Light needed | Very little — night vision | Bright light |
| Color | No | Yes — three spectral types |
| Acuity | Low | High |
| Location | Periphery | Concentrated in the fovea |
Balance organs
2 rows| Organ | Detects | How |
|---|---|---|
| Utricle & saccule | Gravity, linear acceleration | Otoliths shift on a gelatinous membrane |
| Semicircular canals (3) | Rotational/angular acceleration | Fluid deflects the cupula in the ampulla |
Exam traps
8 pairsQuestions get built out of near-misses. If you can state each difference in one sentence, you will not lose those points.
Tonic receptorvsPhasic receptor
Tonic = keeps firing (pain, proprioception — things you must not tune out). Phasic = fires only at the change (smell, light touch). Mnemonic: pha_s_ic = _s_tops.
Utricle/sacculevsSemicircular canals
Otolith organs = straight-line motion and gravity. Semicircular canals = spinning. Three canals for three planes of rotation.
RodsvsCones
Rods = dim light, no color, periphery. Cones = bright light, color, fovea. "Cones for Color."
Light effect on photoreceptorsvsLight effect on typical receptors
Photoreceptors HYPERPOLARIZE in light and release LESS glutamate. Nearly every other receptor depolarizes when stimulated. This is the most common trick question in the chapter.
Base of basilar membranevsApex of basilar membrane
Base = narrow and stiff = HIGH frequency. Apex = wide and floppy = LOW frequency.
Salty/sour tastevsSweet/bitter/umami taste
Salty and sour act directly on ion channels. Sweet, bitter, and umami use G-protein-coupled receptors with gustducin.
Smell pathwayvsAll other sensory pathways
Smell goes straight to olfactory/limbic cortex without a thalamic relay. Every other major sense relays through the thalamus first.
FoveavsOptic disc
Fovea = all cones, sharpest vision. Optic disc = no photoreceptors at all, the blind spot.