The perception of time

Abstract

Any biological organism and especially all human beings depend in their existence on the ability to sense and the environment. To sense the environment means to be able to react to stimuli from the outside of the organism, either physical or chemical stimuli, and to transform these stimuli into electrical signals which can be further processed and interpreted by the brain. For this purpose the organism is equipped with a variety of sensory organs or systems which are specialized in certain modalities. A sensory system can be based on a specific cell-membrane based receptor mechanism or can be unspecified. Although historically also used for complete cells the terminus receptor today more often is used for a cell-membrane incorporated protein-molecule which reacts to the given stimulus by a conformational change and by this triggers further biochemical and electrical events within a cell. These finally induce action potentials, or change frequencies of action potentials, which are transmitted to the central nervous system and processed there. Finally after additional treatment, the stimulus is mentally recognized. The construction of a typical receptor based system is outlined in figure 1. Here the components are classified due to their functional aspects together with the biochemical basis of such functions. Unspecified sensory systems have no receptor, but often the complete cell-membrane fulfils the same task.