It has been believed generally that there are only four basic taste sensations: sweet, sour, salty, and bitter. Some other taste sensations that are frequently mentioned are alkaline, metallic, and umami, which detects monosodium glutamate (MSG), a flavor enhancer often used in Chinese cooking. Different tastes are experienced by combining the four basic taste sensations. Some individuals claim that with the senses of smell and taste working together, an individual can experience 10,000 different combinations.
The tongue is covered in taste buds that send neural signals to the brain. (From Bear, M.F., Connors, B.W., and Parasido, M.A. Neuroscience: Exploring the Brain. 2nd Ed. Philadelphia: Lippincott, Williams & Wilkins, 2001.)