cell signaling

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 (ligands) may be the cell itself (autocrine), adjacent cells (paracrine), the plasma membrane of adjacent cells (contact inhibition), or distant cells (endocrine).

Received signals are transduced into cellular effects by a variety of signal → receptor → enzyme → cellular impact pathways. Extracellular signals impinge upon specialized membranous receptors. Sensory transduction involves the conversion of mechanical or chemical stimuli to cellular signals or neurophysiological signals. Intracellular signals enable communication within cells, while intercellular signals enable communication between cells.

Neurotransmission incorporates interaction between neurotransmitters and specific receptor proteins. 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. Since signaling processes regulate fundamental cellular responses, disturbance of these processes can lead to the development of various human diseases involving disruptions of immunity, abnormal proliferation (cancers), or metabolic disturbance (endocrine disorders).