The sensitive plant, Mimosa pudica, lacks nervous and muscle tissue but exhibits touch-sensitive leaf movements. Rapid leaf folding is triggered by a process called thigmonasty. Specialized cells, called pulvini, are concentrated at the base of leaflets and actively pump potassium ions in response to touch. This ion movement results in a rapid loss of turgor pressure, causing cell collapse and reversible leaf folding. The response is thought to be a defense mechanism against herbivores. While lacking a nervous system, the plant employs these specialized cells and ion movements to detect touch and initiate rapid leaf movements in response to mechanical stimulation.