Senses

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senses, also called sensory reception or sense perception, means by which animals detect and respond to stimuli in their internal and external environments. The senses of animals are most usefully described in terms of the kind of physical energy, or modality, involved. There are four main modalities: the light senses (photoreception; i.e., vision), the mechanical senses (mechanoreception; i.e., touch, balance, and hearing), the chemical senses (chemoreception; i.e., taste and smell), and the electric sense (electroreception) of certain fish. In addition to these external senses there are also internal senses that use the same modalities. For example, there are proprioceptors, which are mechanical sensors that measure the lengths of muscles and positions of joints, and there are interoceptors that monitor blood pressure. Similarly, there are chemoreceptors that monitor blood CO₂ (carbon dioxide) and pH levels, as well as a variety of receptors that respond at the cellular level to the presence of hormones and metabolites.