negative feedback loops

• • Negative feedback loops promote stability in an organism's internal environment
• • Stage 1: detecting the change (stimulus) from the stable state)
• • Stage 2: counteracting the change (response) to return to the stable state
• • The negative feedback mechanisms that maintain homeostasis can be controlled by the nervous system, endocrine system or a combination of both, depending on which particular condition in the internal environment is involved
• • Steps of the negative feedback loop:
  • The system is normal/stable state

  1. Stimulus– change occurs
  2. Change is detected by an appropriate receptor
  3. The receptor sends a signal to the control centre (e.g hypothalamus)
  4. The control centre sends a signal to an appropriate effector (muscles or endocrine glands)
  5. The effector initiates a response
• • normal/stable state restored
• • Once receptors detect acceptable levels, the control centre directs the effector to cease its actions
• • 2 negative feedback loops operate to counter movement in either direction ( increase or decrease) away from the normal state (narrow range) 
• • ALWAYS DRAW negative feedback loops as 2 loops that show what happens if there is a decrease or an increase from the normal/stable state, UNLESS specified in the Q
• • Be sure to include what is involved in each key step of stimulus, receptor, control centre, effector, and response for the return to the normal/stable state