AQA Biology 4.5.2.1 · Combined 4.5.2

Reflex actions

Your hand leaves the hot tray before you know it’s hot. Build the arc that does it, one structure at a time.

Combined Science · Foundation tier

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Oven tray.

You brush the edge of a hot oven tray with the back of your hand.

If you had to guess, did you move first, or feel the pain first?

Reflex arc

Build the reflex arc.

Reflex actions are automatic and rapid; they do not involve the conscious part of the brain. The hand-withdrawal reflex passes through the spinal cord. Pick the next structure each time, synapses included.

Heat on the skin of the hand. What comes next?

Why so fast

Reflex or decision.

A response you decide on goes up to the conscious brain and back down. A reflex does not. Compare the two routes.

Pick a route.

Reflexes are important because they protect the body from harm, for example from burns or from something flying at your eye. Tap each reflex.

Measuring how fast you react when you do decide: Reaction time.

Think again · faster nerves?

“Reflexes are faster because those nerves are faster.”

Your call

Choose

Why is a reflex faster than a response you decide on?

Sort

Reflex or not?

Place each one.

Tap a card, then tap the box it belongs in. Tap a placed card to take it back.

Command words in this lesson

Describe: The reflex arc, structure by structure, in order.
Explain: Why a reflex is faster than a voluntary response.
Suggest: Why a reflex protects the body.

Key fact

A reflex is automatic and rapid. Receptor, sensory neurone, synapse, relay neurone, synapse, motor neurone, effector, with no conscious brain involved.

Key note · AQA 4.5.2.1 (Combined 4.5.2)

Reflex actions

Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.
Arc: stimulus, receptor, sensory neurone, synapse, relay neurone, synapse, motor neurone, effector, response.
At each synapse a chemical is released, diffuses across and starts a new impulse.
Faster: shorter pathway, fewer synapses, no conscious brain. Reflexes protect the body from harm.

Photograph this card. Tomorrow, cover it and say each line first.

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Not sure where the synapses go in the arc?

Figures are schematic.