Signaling between cells in physical contact.

The signal finally triggers a specific cellular activity, such as gene expression or enzyme activation. Types of Signaling: Autocrine: A cell targets itself.

The receptor triggers a relay of intracellular molecules, often called a signaling cascade (e.g., using G-proteins or kinases).

A signaling molecule (ligand) binds to a specific receptor on the cell surface or inside the cell.

Nearby cells are targeted (e.g., neurotransmitters).

Cell signaling is the complex process by which cells perceive and respond to their environment. It is essential for homeostasis, growth, and immune responses.