Taste is the ability to respond to dissolved molecules and ions called tastants. Humans detect taste with taste receptor cells. These are clustered in taste buds. Each taste bud has a pore that opens out to the surface of the tongue enabling molecules and ions taken into the mouth to reach the receptor cells inside. There are five primary taste sensations:
Properties of the taste system.
•A single taste bud contains 50–100 taste cells representing all 5 taste sensations (so the classic textbook pictures showing separate taste areas on the tongue are wrong). •Each taste cell has receptors on its apical surface. These are transmembrane proteins which oadmit the ions that give rise to the sensations of salty and sour; obind to the molecules that give rise to the sensations of sweet, bitter, and umami. •A single taste cell seems to be restricted to expressing only a single type of receptor (except for bitter receptors). •Taste receptor cells are connected, through an ATP-releasing synapse, to a sensory neuron leading back to the brain. •However, a single sensory neuron can be connected to several taste cells in each of several different taste buds. •The sensation of taste — like all sensations — resides in the brain [evidence]. •And in mice, at least, the sensory neurons for four of the tastes (not sour) transmit their information to four discrete areas of the brain. Salty
In mice, perhaps humans, the receptors for table salt (NaCl) is an ion channel that allows sodium ions (Na+) to enter directly into the cell. This depolarizes it allowing calcium ions (Ca2+) to enter [Link] triggering the release of ATP at the synapse to the attached sensory neuron and generating an action potential in it. In lab animals, and perhaps in humans, the hormone aldosterone increases the number of these salt receptors. This makes good biological sense: •The main function of aldosterone is to maintain normal...