A negative feedback control system has the following elements:

An illustration depicts the basic constituents of a negative feedback control system. The system comprises of the following: Signal from the sensor, which measures controlled variable, is passed on to the comparator. Set point is preset in the comparator, which recognizes deviations from normal set point value. Error signal is passed on to the effector from the comparator. It can be either stimulatory or inhibitory. Effector attempts to restore set point value and passes on inhibitory signal to controlled variable. This is negative feedback, where effector opposes stimulus. Controlled variable is an important variable maintained within narrow normal limits, and further passes on signal to the sensor, thus completing the loop.

 

  1. A set point value, which is at the center of the normal range and is treated by the control system as the target value.

  2. Sensors that monitor the controlled variable.

  3. A comparator, which interprets input from the sensors to determine when deviations from the set point have occurred. The comparator initiates a counter response.

  4. Effectors are the mechanisms that restore the set point.

     

    Using the control of blood pressure as an example:
    1. The controlled variable is mean arterial blood pressure (MAP).

    2. The normal set point for MAP is approximately 95 mm Hg.

    3. Pressure sensors are located in the carotid sinus and relay information to a comparator located in the central nervous system.

    4. If MAP suddenly changes, the activity of effectors (e.g., cardiac contractility, vascular tone, and urinary fluid excretion) is altered to restore normal blood pressure.]