ABSTRACT
Chemical senses are used by living organisms to gather chemical information from the external and internal environment. Chemical reception can be demonstrated in the simplest of organisms, such as microbes. One such organism is the ciliated protozoan Paramecium tetraurelia. Tetraurelia exhibits Chemotaxis, that is, modulation of behavior that results from sensing the chemical composition of its immediate environment. aste sensations are conveyed by two different cranial nerves, VII and IX. The neural pathways of the gustatory system are uncrossed, an exception to the pattern exhibited by all other sensory pathways. In the medulla, neurons carrying taste messages synapse with the cell bodies of second-order neurons. The fibers of the second-order neurons synapse in the thalamus in the ventral posterior medial nucleus. A plausible explanation of how the stimulus of gustation might be transduced into a neural stimulus is the assumption that the oral cavity contains receptors that are sensitive to the chemical configuration of certain molecules.
