Final answer:
An effector is a muscle or motor nerve that carries out a response to a stimulus. It is an important part of the motor pathway in the nervous system.
Step-by-step explanation:
An effector is a muscle or motor nerve that is responsible for carrying out a response to a stimulus. It is usually involved in motor functions and is part of the efferent (or motor) pathway of the nervous system.
For example, when a person touches something hot, the sensory neurons in the skin detect the heat and send a signal to the central nervous system (CNS). The CNS then sends a signal to the motor neurons, which in turn activate the muscles of the hand to quickly retract it from the hot object. Here, the muscles act as effectors by contracting in response to the signal from the motor neurons.
Therefore, the statement is true. An effector is usually a muscle or motor nerve.