Smakscellene

Smakscellene (taste cells) are specialized sensory cells that detect chemical compounds dissolved in saliva and convey information about taste to the nervous system. They reside mainly within taste buds, small clusters located on the tongue's surface in the fungiform, circumvallate, and foliate papillae, and also on the soft palate, pharynx, and epiglottis. A taste bud contains several gustatory receptor cells, along with supporting and basal cells.

Taste receptor cells are categorized into three main types. Type II receptor cells detect sweet, bitter, and umami via GPCRs (T1R and T2R families) and release ATP as a transmitter; Type III presynaptic cells detect sour and form conventional synapses with gustatory afferent fibers. Type I glial-like supporting cells provide structural support and help maintain the extracellular environment.

Signal transduction: Sweet, umami, and bitter receptors recruit G-protein signaling (gustducin), activate PLCβ2, IP3, release Ca2+, leading to release of ATP as neurotransmitter to afferent nerve endings. Saltiness is produced by sodium ions entering through amiloride-sensitive ENaC channels, depolarizing taste cells; sourness involves proton-sensitive mechanisms, including various ion channels, with PKD2L1 implicated in some studies.

Innervation and central processing: Taste signals are carried by the chorda tympani (CN VII) for the anterior tongue, the glossopharyngeal nerve (CN IX) for the posterior tongue, and the vagus nerve (CN X) for the palate and epiglottis. Signals reach the nucleus of the solitary tract, then the ventroposterior medial nucleus of the thalamus, and finally the gustatory cortex in the insula and frontal operculum.

Regeneration and clinical relevance: Taste cells renew continuously, with an estimated turnover of about 10–14 days from basal progenitors. Taste disorders can result from illness, medications, or damage to cranial nerves, reducing taste (hypogeusia) or causing complete loss (ageusia). Taste is also influenced by smell and overall oral health.