Taste begins with sensation in the form of electrical impulses. Sensations, however -- responses to stimuli like pressure, light or chemical composition -- become perceptions like touch, vision or taste only when they reach the brain.
Different stimuli activate different sensory receptors. Chemical stimuli activate the chemoreceptors responsible for gustatory and olfactory perceptions. Because taste and smell are both reactions to the chemical makeup of solutions, the two senses are closely related. If you've ever had a cold during Thanksgiving dinner, you know that all of the subtlety of taste is lost without smell.
In some species, however, the two chemical senses are practically one. Invertebrates like worms do not have distinctions between gustatory and olfactory receptors. They instead differentiate between volatile and nonvolatile chemicals.
In humans, the chemoreceptors that detect taste are called gustatory receptor cells. About 50 receptor cells, plus basal and supporting cells, make up one taste bud. Taste buds themselves are contained in goblet-shaped papillae -- the small bumps that dot your tongue. Some papillae help create friction between the tongue and food.
Every gustatory receptor cell has a spindly protrusion called a gustatory hair. This taste hair reaches the outside environment through an opening called a taste pore. Molecules mix with saliva, enter the taste pore and interact with the gustatory hairs. This stimulates the sensation of taste.
Once a stimulus activates the gustatory impulse, receptor cells synapse with neurons and pass on electrical impulses to the gustatory area of the cerebral cortex. The brain interprets the sensations as taste.
In the next section, we'll learn about the primary tastes and how taste gives us clues about what we eat.