The areas of the tongue sensitive to tastes. The classical theory about the physiology of taste recognizes the existence of four fundamental tastes - sweet, salty, sour and bitter - each being perceived by specific areas of the tongue by means of gustatory receptors, also known as taste buds.
Theories of Aging. Theories of Aging. Erik Erikson, who took a special interest in this final stage of life, concluded that the primary psychosocial task of late adulthood (65 and beyond) is to maintain ego integrity (holding on to one's sense of wholeness), while avoiding despair (fearing there is too little time to begin a new life course).
The Wear and Tear Theory of Aging. The wear and tear theory of aging believes that the effects of aging are caused by damage done to cells and body systems over time. Essentially, these systems wear out due to use. Once they wear out, they can no longer function correctly.