The central nervous system (brain and spinal cord) is the command centre: sensory neurons carry impulses in from receptors, motor neurons carry them out to effectors. Reflexes go through the spinal cord without waiting for the brain.
Step on a pin and your foot is off the floor before you've said 'ouch'. Your brain wasn't the one who decided.
Every response follows the same pathway. This lesson: building the pathway yourself, and which part of the nervous system decides.
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: who moves your foot?
ExploreTry it on the board and compare what happens with your prediction.
Explore: build the pathway
Pick a stimulus, then choose its receptor, command centre and effector, and send the signal.
Try it yourselfYour edits are saved in this browser.
Build three pathways correctly, including the drawing pin.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: the nervous system
In your book: draw the reflex arc for the drawing pin, labelling the receptor, sensory neuron, spinal cord, motor neuron and effector.
Match each part of the nervous system to its place in the pathway.
Sensory neuron
Brain and spinal cord (CNS)
Motor neuron
Receptor
Elaborate TypicalUse the same idea in a new context.
Elaborate: reflex or not?
Reflex (automatic, no decision) or a decided response?
Blinking when something flies at your eye
Answering a question in class
Pupils narrowing in bright light
Choosing a snack
Knee jerking when tapped below the kneecap
Catching a ballPractice makes it fast, but the brain still judges where the ball will go.
Elaborate WiderUse the same idea in a new context.
Elaborate: damage to the pathway
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
The central nervous system (brain and spinal cord) is the command centre.
Sensory neurons carry impulses from receptors to the CNS; motor neurons carry them to effectors (muscles or glands).
A reflex is automatic and fast: the impulse goes through the spinal cord without waiting for the brain.
For teachers
Students build stimulus–response pathways, name the CNS as the command centre with sensory and motor neurons, and explain why reflexes are fast (AC9S9U01, node 2, a hinge node). About 20 minutes.
I can build a stimulus–response pathway, choosing the receptor, command centre and effector.
I can name sensory and motor neurons and the CNS.
I can explain why a reflex is faster than a decided response.
Before class
A concept tutorial for introducing or revising the idea; it does not replace the ruler-drop practical. Set the width with ?width=minimum, typical (default) or wider.
The hinge misconception is that the brain decides every response. The drawing pin is a required pathway.
Board notes: the menus mix receptors, command centres and effectors from all four stimuli; a wrong choice names the first step that is wrong.
Running the lesson
Engage: count how many chose 'the brain'.
Explore: watch for students choosing the brain for the pin; let the board's message do the work.
Explain: the reflex question is the checkpoint.
The hard part (on purpose)
Tracing the path through the spinal cord for a reflex. When a student says the brain decides everything, ask whether you feel the pain before or after your foot moves.
When students get stuck
A student chooses the brain as the command centre for the drawing pin. Ask: Do you feel the pain before or after your foot moves? Fix: After: the spinal cord moved the foot, then the brain found out.
A student says the salivary glands can't be an effector. Ask: What does an effector do? Fix: It carries out the response; glands do that by releasing a substance.
Stretch and support
Stretch: Why might it be useful that the brain can override some reflexes (holding a hot plate you can't drop)?
Support: Give a reflex-arc diagram with blanks: receptor, sensory neuron, spinal cord, motor neuron, effector.
Where it leads
Next: nerves versus hormones (node 4), then feedback (node 5).
In class: ruler-drop reaction times with and without distraction; knee-jerk reflex.
What each step is for
Engage: who moves your foot?: Students who believe the brain makes every decision will choose it for the pin; the reflex arc goes through the spinal cord.
Explore: build the pathway: Choosing each part, with feedback on the first wrong one, forces students to decide what detects, what decides and what acts.
Explain: the nervous system: Mapping sensory neuron, CNS and motor neuron onto the pathway connects the boxes to the body.
Elaborate: reflex or not?: Sorting reflexes from decided responses uses the 'does it need the brain to decide?' test.
Elaborate: damage to the pathway: Predicting the effect of a break at one point shows the pathway is a chain.
Now you can
Build a stimulus–response pathway, choosing the receptor, command centre and effector.
Name sensory and motor neurons and the CNS.
Explain why a reflex is faster than a decided response.