A "ligand-gated" channel is a type of protein found in cell membranes that opens or closes in response to the binding of a specific molecule, known as a ligand. When the ligand attaches to the channel, it causes a change in the channel's shape, allowing ions or other substances to flow into or out of the cell. This process is crucial for various cellular functions, including signaling and communication between cells. These channels play a vital role in the nervous system, where they help transmit signals between neurons. For example, when a neurotransmitter binds to a ligand-gated channel on a neuron, it can trigger an electrical impulse, leading to the propagation of a signal. This mechanism is essential for processes such as muscle contraction and sensory perception.