Nerves and reflexes Cambridge IGCSE Co-ordinated Sciences (Double Award) revision
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In plain words
Touch something hot and your hand is gone before you've even felt the pain. That's a reflex: a message takes a short cut through your spinal cord and comes straight back to the muscle, without waiting for your brain. Nerves carry messages as electrical signals, very fast.
Three things to know
- The central nervous system (CNS) is the brain and spinal cord. Nerves carry electrical impulses between it and the rest of the body.
- A reflex arc: stimulus → receptor → sensory neurone → relay neurone (in the CNS) → motor neurone → effector (a muscle or gland) → response. Reflexes are fast and automatic, which protects the body.
- A synapse is the tiny gap between two neurones. The impulse can't jump it, so a chemical (a neurotransmitter) is released, diffuses across and starts a new impulse on the other side.
Tips and tricks
- Learn the reflex arc as a chain and write it with arrows. Each link is a mark.
- Sensory neurones carry impulses to the CNS; motor neurones carry them away, to the effector.
It lands in your notebook with its questions as flashcards.
Nerves and reflexes: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What makes up the central nervous system?
Everything else is the peripheral nervous system.
Which neurone carries impulses from a receptor to the CNS?
Sensory neurones bring information in.
What is an effector?
It is what does something in response.
How does a signal cross a synapse?
The chemical is a neurotransmitter.
Why are reflex actions useful?
There is no delay while the brain decides what to do.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 9 marks. Write your answers on paper, then check them.
Nerves and reflexes
Cambridge IGCSE Co-ordinated Sciences (Double Award) 0654 · 9 marks · papermunch.org
Name ______________________________ Date ______________
Describe the path of a reflex arc when a person touches a hot object.[4]
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Receptors in the skin detect the heat (stimulus). An impulse travels along a sensory neurone to the spinal cord, across a relay neurone, and out along a motor neurone to a muscle (the effector), which contracts and pulls the hand away.
State two features of a reflex action.[2]
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It is rapid, and it is automatic (not under conscious control).
Describe how an impulse passes across a synapse.[3]
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A neurotransmitter is released from the end of the first neurone. It diffuses across the gap and binds to receptors on the next neurone, starting a new impulse there.
Answers: Nerves and reflexes
- 1. Receptors in the skin detect the heat (stimulus). An impulse travels along a sensory neurone to the spinal cord, across a relay neurone, and out along a motor neurone to a muscle (the effector), which contracts and pulls the hand away.
- 2. It is rapid, and it is automatic (not under conscious control).
- 3. A neurotransmitter is released from the end of the first neurone. It diffuses across the gap and binds to receptors on the next neurone, starting a new impulse there.