A stimulus is any change the body detects, outside it or inside it. Every response follows the same pathway: stimulus, receptor, command centre, effector, response.
You pull your hand off a hot pan before you feel the pain. After lunch, your blood sugar is brought back down without you noticing at all. Both are responses to a stimulus.
Earlier you met body systems. This lesson: how the body detects change and responds.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: what is a stimulus?
ExploreTry it on the board and compare what happens with your prediction.
Explore: follow the signal
Click a stimulus to send it through the pathway. Notice which ones are internal and which are external.
Try it yourselfYour edits are saved in this browser.
Follow at least four stimuli through the pathway, including two internal ones.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: the pathway
In your book: draw the pathway for one internal stimulus, labelling every box.
Internal or external stimulus?
A loud bang
Blood sugar rising
The smell of toast
Body temperature falling
Too little water in the blood
Cold wind on your skinThe wind is outside; your body temperature falling because of it is an internal change.
Match each part of the pathway to what it does.
Stimulus
Receptor
Command centre
Effector
Response
Elaborate TypicalUse the same idea in a new context.
Elaborate: a new pathway
A runner's muscles use oxygen fast, so carbon dioxide in the blood rises. Breathing speeds up. Sort each into its part of the pathway.
Carbon dioxide in the blood rises
Chemical receptors in blood vessels and the brain
Brain stem
Diaphragm and rib muscles
Faster, deeper breathing
Elaborate WiderUse the same idea in a new context.
Elaborate: plants respond too
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
A stimulus is any change the body detects, external (light, heat, sound) or internal (blood sugar, temperature, water).
Stimulus → receptor → command centre → effector → response.
Receptors detect; the brain, spinal cord or a gland decides; muscles and glands are the effectors.
For teachers
Students identify stimuli as internal or external changes and trace them through the stimulus–response pathway (AC9S9U01, node 1, a hinge node). About 20 minutes.
I can explain that a stimulus is a change inside or outside the body.
I can name the parts of the stimulus–response pathway and what each does.
I can trace an internal and an external stimulus through the pathway.
Before class
A concept tutorial for introducing or revising the idea; it does not replace a reaction-time practical (the ruler drop) or the knee-jerk reflex. Set the width with ?width=minimum, typical (default) or wider.
The hinge misconception is that stimuli are only external. Three of the five board stimuli are internal on purpose.
Board notes: each pathway is simplified to one receptor, one command centre and one effector; the blood sugar and water pathways mix glands and hormones into the boxes, which the next lessons separate.
Running the lesson
Engage: count how many chose 'only things outside you'.
Explore: ask which stimuli they would never notice happening.
Explain: the sort is the checkpoint; 'cold wind' prompts the external change / internal effect distinction.
The hard part (on purpose)
Placing each part on the pathway, especially changes inside the body. When a student skips one, ask what detects the change and what carries out the response.
When students get stuck
A student says blood sugar isn't a stimulus because you can't feel it. Ask: Did the body detect it and respond? Fix: Yes: cells in the pancreas detect it. A stimulus is anything the body detects, felt or not.
A student calls the skin the effector. Ask: Does the skin detect the heat or move the hand? Fix: It detects it: receptors. Muscles and glands are effectors.
Stretch and support
Stretch: In the water pathway, the response makes the stimulus go away. Find another pathway on the board where that happens.
Support: Give a five-box strip to fill in for each stimulus clicked.
Where it leads
Next: building pathways yourself and why the command centre matters (node 2), then nerves versus hormones (node 4) and feedback (node 5).
In class: ruler-drop reaction times; knee-jerk reflex; pupil response with a torch.
What each step is for
Engage: what is a stimulus?: Students who think stimuli are only things outside the body (light, sound, touch) will pick the narrow answer; the board includes changes inside.
Explore: follow the signal: Watching five different stimuli travel through the same five boxes makes the pathway a pattern, not a list to memorise.
Explain: the pathway: Naming the part each step plays, and sorting internal from external, are the two pieces of the hinge.
Elaborate: a new pathway: Applying the pathway to an unseen example shows the pattern has transferred.
Elaborate: plants respond too: Plants detect and respond to stimuli without nerves, which separates the pathway idea from the nervous system.
Now you can
Explain that a stimulus is a change inside or outside the body.
Name the parts of the stimulus–response pathway and what each does.
Trace an internal and an external stimulus through the pathway.