Thirst and Hunger: General Sensations

Abstract

The feeling of thirst we experience when we have not drunk enough fluids, and our feelings of hunger when we have not eaten recently, cannot be ascribed to a particular sense organ or part of the body. For this reason they are called “general sensations”. Other examples of general sensations are tiredness, shortness of breath, and sexual appetite. From the viewpoint of sensory physiology, a characteristic they all share is that they can be elicited by one or more adequate stimuli originating within the body itself, rather than in its environment. These stimuli are detected by receptors, some of which are still unknown, and thus produce the associated general sensations (Fig. 10-1A). For example, we shall explain below that a “concentrating” of the body fluid due to lack of water is sensed by osmoreceptors, the result being a sensation or feeling of thirst (Fig. 10-1B). One can also imagine that during the course of the day waste materials accumulate in the blood, and that these are responsible for a feeling of tiredness (cf. Sec. 9.2 in Fundamentals of Neurophysiology), or that certain hormones elicit feelings of sexual desire, or favor the occurrence of such feelings, when their concentration in the body is high enough.