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Homeostasis regulates internal conditions within useful limits despite external changes. Receptors detect a stimulus, a coordination centre processes information and effectors produce a response. Negative feedback reduces a deviation from a target. Examples include temperature and blood glucose, but the target is not necessarily one exact fixed value in all circumstances. A feedback explanation should identify the detected change, coordinating action and resulting corrective effect.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Explain the receptor–coordinator–effector pathway
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: What does negative feedback do?
Reduces a deviation. It helps stabilise internal conditions.
After watching 2: Which neurone carries impulses to an effector?
Motor neurone. Motor output activates the response.
What you'll be able to do
Homeostasis regulates internal conditions within useful limits despite external changes. Receptors detect a stimulus, a coordination centre processes information and effectors produce a response. Negative feedback reduces a deviation from a target. Examples include temperature and blood glucose, but the target is not necessarily one exact fixed value in all circumstances. A feedback explanation should identify the detected change, coordinating action and resulting corrective effect.
A sensory neurone carries an impulse from a receptor toward the central nervous system, relay neurones connect within it, and a motor neurone carries output to an effector such as muscle. At synapses, chemicals cross a small gap and trigger the next cell. A reflex is rapid and automatic and can protect against damage. The brain can receive information about the event, so automatic does not mean the nervous system never informs the brain.
The retina detects light, while the iris changes pupil size to regulate entry. For near focus, ciliary muscles contract, suspensory ligaments slacken and the lens becomes thicker. For distant focus the reverse changes occur. The pupil is an opening, not a muscle. Brain regions have different roles, but studying the brain is difficult because it is complex and damage can be serious. Evaluate evidence from scans and injury studies with those limitations.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: What changes in the lens for near focus?
A thicker lens focuses nearby objects.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.