Cell Signaling
Cell signaling refers to the complex system of communication by which cells detect, process, and respond to chemical signals from their environment or neighbouring cells. Signaling pathways typically involve a ligand binding to a receptor, triggering an intracellular cascade of molecular events that alter gene expression, metabolism, or cell behaviour. It governs fundamental processes such as growth, differentiation, immune responses, and apoptosis.
Major Types of Cell Signaling
| Type | Distance | Mechanism | Example |
|---|---|---|---|
| Autocrine | Same cell | Cell signals to itself | Growth factors in cancer |
| Paracrine | Adjacent cells | Local diffusion of signal | Neurotransmitter release at synapse |
| Endocrine | Distant (systemic) | Hormones via bloodstream | Insulin from pancreas to liver |
| Juxtacrine | Direct contact | Membrane-bound ligand to receptor | Notch-Delta signaling |
| Synaptic | Neuron to target | Neurotransmitter across synapse | Acetylcholine at NMJ |
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Related Terms
Apoptosis
Apoptosis is a form of programmed, genetically regulated cell death that occurs in multicellular organisms as a normal and controlled part of development and homeostasis. It is characterised by cell shrinkage, chromatin condensation, membrane blebbing, and fragmentation into apoptotic bodies that are cleared by phagocytes without triggering inflammation. Dysregulation of apoptosis is implicated in cancer (insufficient apoptosis) and neurodegenerative diseases (excessive apoptosis).
Membrane Potential
Membrane potential is the electric potential difference across a cell's plasma membrane, arising from the unequal distribution of ions (Na⁺, K⁺, Cl⁻, Ca²⁺) between the intracellular and extracellular environments. In neurons and muscle cells, the resting membrane potential is approximately −70 mV (inside negative), maintained by the Na⁺/K⁺-ATPase pump and selective ion channels. Changes in membrane potential — action potentials — underlie nerve impulse transmission and muscle contraction.
Cell Cycle
The cell cycle is the ordered sequence of events by which a cell grows, replicates its DNA, and divides into two daughter cells. It consists of interphase (G1, S, and G2 phases) and the mitotic phase (mitosis and cytokinesis). Precise regulation of the cell cycle through checkpoints is essential for normal development; dysregulation leads to cancer and other diseases.
From Latin "cella" (small room) + Latin "signum" (mark, signal). The systematic study of cell signaling emerged in the 1950s–1970s with the discovery of cyclic AMP as a second messenger by Earl Sutherland, who won the 1971 Nobel Prize in Physiology.