A feedback loop is a closed loop whose output is used to regulate the input, or, in other words, is "fed back" to whatever is controlling the input.
- A positive feedback loop encourages changes in the output. For example, if an increase in X causes an increase in Y, when Y increases, the feedback loop will cause X to also increase to further the change.
- A negative feedback loop resists changes in the output in order to maintain a setpoint. For example, if an increase in X causes an increase in Y and the setpoint of Y is zero, when Y increases, the feedback loop will cause X to decrease to restore Y to the setpoint, and if Y decreases, it will cause X to increase.
Components of a feedback loop:
- Stimulus
- A stimulus of something is an event or force which triggers a response from it.
- The stimuli of this system are forces which affect the body's internal temperature. We are specifically exploring the temperature of the environment and the production of heat internally by muscle activity.
- Sensor or Receptor
- In the body, a sensor monitors a particular body condition and signals its current state to the brain. In the case of temperature, there are two types of sensors, one for heat and one for cold, and the brain reads both to get a more accurage idea of the current temperature.
- In this system, the sensors are thermoreceptors, found in the dermis (skin), skeletal muscles, liver, and hypothalamus. There are two different types, one that signals cold temperatures and one that signals hot temperatures, and the brain reads both to more accurately assess the body's internal temperature.
- Control Center
- The control center monitors the current conditions, determines the appropriate response, and commands the effector(s) to perform it.
- In this system, the control center is the hypothalamus, an area of the brain, which reads the thermoreceptors and commands the effectors (listed below) to respond appropriately.
- Effector or Response
- An effector, upon receiving a signal from the brain, carries out the action it is designed to do in order to affect the change desired by the feedback loop.
- In this system, the effectors are pores, which allow sweating in response to hot temperatures, and muscles, which shiver in response to low temperatures.
The negative feedback loop that regulates the body's internal temperature is modeled below.
