Tonic

Tonic, in physiology, refers to the consistent, baseline level of activity maintained by certain muscles or nerves. It helps maintain posture and readiness by providing a steady, ongoing signal. For example, in muscle function, tonic activity ensures muscles stay slightly contracted even when not actively moving, supporting stability. This contrasts with phasic activity, which involves quick, transient movements. Tonic responses are crucial for sustained control and balance in the body, allowing us to stand, sit, and maintain positions without constant active effort.