- noun a substance such as a hormone, neurotransmitter or drug that binds to a cell’s receptors to trigger a response
- noun a muscle which causes part of the body to move and another muscle to relax when it contracts.
- noun a substance which produces an observable physiological effect by acting through specific receptors.
- noun a muscle whose action is balanced by that of another associated muscle
- noun a hormone, neurotransmitter or drug that triggers a response by binding to specific cell receptors