cellular signalling

Cells, whether unicellular organisms or cells within multicellular organisms, respond to signals within their environment. Such signals include mechanical stimuli (light, sound) and chemicals. The origin of chemical stimuli may be the cell itself (autocrine), adjacent cells (paracrine), the plasma membrane of adjacent cells (contact inhibition), or distant cells (endocrine). Cytokines mediate paracrine stimulation, and hormones mediate endocrine stimulation.

Cellular responses to signalling molecules include alterations in gene expression (transcription), alteration of electrophysiological charge, and alteration of metabolic activity of the cell.