Taste and smell !

Mechanism
For completeness

Taste buds detect five basic tastes; the nose adds thousands of smells. Together they make flavour.

Updated 2026-11-01

Also called: Gustation, Olfaction

See it in 3D: Tongue · Olfactory nerve (I) · Cribriform plate · Facial nerve (VII) · Glossopharyngeal nerve (IX) · Vagus nerve · Insula · Nasal cavity

What it is

Taste receptor cells in taste buds detect sweet, umami, bitter, salty and sour; three cranial nerves carry the signals to the brainstem and thalamus. Olfactory neurons in the roof of the nose each express one odorant receptor type and send axons through the cribriform plate to the olfactory bulb. Most of what people call taste is actually smell.

How it works, step by step

Tastants dissolve in saliva and reach receptor cells at the taste pore.
Sweet, umami and bitter molecules bind GPCRs; a second-messenger cascade releases Ca²⁺ and ATP, activating afferent fibres.
Salt enters through epithelial Na⁺ channels and sour (H⁺) through proton channels, depolarizing their receptor cells directly.
Odorants dissolve in nasal mucus and bind odorant receptors on cilia of olfactory neurons.
A G protein (Golf) raises cAMP, opening cyclic-nucleotide-gated cation channels; Ca²⁺-activated Cl⁻ outflow amplifies depolarization.
Axons cross the cribriform plate and converge on glomeruli of the olfactory bulb, one glomerulus per receptor type, building an odour map.
Mitral cells project to the piriform cortex, amygdala and entorhinal cortex; the orbitofrontal cortex combines smell and taste into flavour.

Approximate numbers

Parameter	Value	Note
Taste buds	≈2000–5000	varies widely between people
Taste receptor cell lifespan	≈1–2 weeks	constantly renewed
Functional odorant receptor genes	≈350–400	combinations code many thousands of odours

Approximate values for a healthy adult at rest; each laboratory sets its own ranges.

Clinical notes

Loss of smell was a frequent early symptom of COVID-19, from damage to supporting cells of the olfactory epithelium.
Facial nerve lesions proximal to the chorda tympani cause loss of taste on the anterior tongue on that side.
Losing smell removes a safety signal (smoke, gas leaks, spoiled food).

Test yourself

Think of the answer, then tap the question to see it.

Why does food seem tasteless when the nose is blocked by a cold?

Most flavour comes from smell of odorants reaching the nose from the back of the mouth; with the nose blocked, only the five basic tastes remain.

How is salty taste transduced differently from bitter taste?

Na⁺ enters through ENaC channels and depolarizes the cell directly; bitter compounds bind GPCRs (T2R) and act through a second-messenger cascade.

Why can a frontal head injury cause permanent loss of smell?

Olfactory axons cross the thin cribriform plate; a shearing injury or fracture tears them as they pass.

What is unusual about the olfactory pathway compared with other senses?

It reaches the primary olfactory (piriform) cortex directly from the olfactory bulb without an obligatory thalamic relay, with direct links to amygdala and entorhinal cortex.

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See it in 3D

The structures of Durgical's 3D anatomy where it happens.

In Biochemistry

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Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: 14.1 Sensory Perception (OpenStax (Rice University), 2022); Neuroanatomy, Cranial Nerve 1 (Olfactory) (StatPearls (NCBI Bookshelf), 2024); Neuroanatomy, Cranial Nerve 9 (Glossopharyngeal) (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 54). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.