Taste is a sense which allows us to distinguish between different types of food or drink. Using this sense, we can detect the extent to which something is sweet, salty, bitter, and sour. All other tastes come from different combinations of these four primary sensations. Recently, a fifth taste has been discovered called umami which is associated with foods containing glutamate. There are taste receptors distributed on the tongue which set in motion a cascade of downstream biochemical events which allow us to discern the aforementioned tastes when we eat and drink.
There are two primary cranial nerves which innervate the tongue. They include the cranial nerve VII (facial nerve) and cranial nerve IX (glossopharyngeal nerve). Cranial nerve VII is believed to innervate approximately two thirds of the anterior part of the tongue, whereas cranial nerve IX is believed to innervate approximately one third of the posterior portion of the tongue. Cranial nerve X (vagus nerve) further contributes to sending taste related impulses from the back of the mouth. Collectively, these nerves serve as the conduit upon which the initial stimulation of specific taste receptors send cascades of biochemical events to the brain so that we can discern specific taste sensations.