AQA · GCSE · Combined Science

Course version: 8464 · Version from Sept 2018

The human nervous system: Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important.

Q: How do I revise The human nervous system: Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important. for GCSE?

Read the notes on The human nervous system: Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important., then test yourself without looking. Answering questions and checking what you missed builds recall faster than re-reading.

Q: Is this The human nervous system: Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important. guide aligned to the AQA specification?

Yes. This guide is linked to the The human nervous system: Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important. topic in the AQA GCSE specification.

A reflex arc begins when a receptor detects a stimulus and a sensory neurone carries the impulse to the central nervous system.

3 key terms

Study notes

From the checked teaching notes for this specification point.

The idea

What earns the marks

The sensory neurone carries impulses from receptors to the central nervous system and has a cell body positioned alongside the spinal cord.
The relay neurone is located inside the spinal cord or brain and connects the sensory neurone to the motor neurone.
The motor neurone carries impulses from the central nervous system to an effector, such as a muscle or gland.
At a synapse, a neurotransmitter is released from the presynaptic neurone, diffuses across the synaptic gap and binds to receptors on the postsynaptic neurone.
Reflex actions are rapid and automatic because the pathway does not pass through the conscious areas of the brain.
Reflex actions are important because they protect the body from damage, for example withdrawing a hand from a hot object or blinking in response to a bright light.

Common mistakes and how to put them right

Saying that the relay neurone carries impulses from the receptor to the spinal cord.
Put it right: The sensory neurone does that; the relay neurone connects sensory and motor neurones inside the central nervous system.
Describing the synapse as a direct electrical connection.
Put it right: The impulse crosses the synapse by diffusion of a neurotransmitter, which takes a small amount of time.
Claiming that reflex actions are slow because they involve the brain.
Put it right: Reflex actions are rapid because the impulse is coordinated by the spinal cord and does not require conscious processing by the brain.

Exam tips

Label a reflex arc diagram using the terms receptor, sensory neurone, relay neurone, motor neurone, synapse and effector.
When explaining the synapse, state that a neurotransmitter diffuses across the gap and binds to receptors on the next neurone.
Link the speed and automatic nature of reflexes to their protective function, using a named example such as withdrawing a hand from a hot surface.

Try the lesson

The start of the The human nervous system: Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important. lesson, made from checked teaching notes for this specification point.

Have a go first

Which structure carries electrical impulses from a receptor to the coordinator?

Tip: press 1 to 4 to choose

Listen

A reflex arc begins when a receptor detects a stimulus and a sensory neurone carries the impulse to the central nervous system. The sensory neurone has a cell body beside the spinal cord and a long dendron, allowing rapid transmission. At a synapse, the impulse triggers release of a neurotransmitter that diffuses across the gap and stimulates the next neurone. A relay neurone inside the spinal cord links the sensory and motor neurones, and the motor neurone carries the impulse to an effector, such as a muscle, which contracts. Reflex actions are automatic and do not involve conscious thought, so they are rapid and protect the body from harm. A strong answer earns marks for these points. The sensory neurone carries impulses from receptors to the central nervous system and has a cell body positioned alongside the spinal cord. The relay neurone is located inside the spinal cord or brain and connects the sensory neurone to the motor neurone. The motor neurone carries impulses from the central nervous system to an effector, such as a muscle or gland. At a synapse, a neurotransmitter is released from the presynaptic neurone, diffuses across the synaptic gap and binds to receptors on the postsynaptic neurone. A common slip: Saying that the relay neurone carries impulses from the receptor to the spinal cord. Instead, the sensory neurone does that; the relay neurone connects sensory and motor neurones inside the central nervous system. Exam tip: Label a reflex arc diagram using the terms receptor, sensory neurone, relay neurone, motor neurone, synapse and effector.

See it

A flowchart running from top to bottom. The first box says the receptor detects a stimulus and points to the second box, where the sensory neurone carries the impulse to the central nervous system. This points to a third box describing the synapse: neurotransmitter released, diffuses across the gap, stimulates the next neurone. This points to a fourth box where the relay neurone inside the spinal cord links sensory and motor neurones. This points to a fifth box where the motor neurone carries the impulse to an effector, and finally to a sixth box where the effector, such as a muscle, contracts. — It shows the sequence of a reflex arc from receptor to effector, including the synapse and relay neurone.

Put it in order

Put these steps in the order they happen.

1. Sensory neurone carries the impulse to the central nervous system
2. Synapse: neurotransmitter released, diffuses across the gap, stimulates the next neurone
3. Relay neurone inside the spinal cord links sensory and motor neurones
4. Motor neurone carries the impulse to an effector
5. Effector, such as a muscle, contracts
6. Receptor detects a stimulus

Key words

Say what each word means before you turn the card.

Sensory neurone

Try answering aloud or in your head before turning the card.

Relay neurone

Try answering aloud or in your head before turning the card.

Motor neurone

Try answering aloud or in your head before turning the card.

See every definition

Sensory neurone: Carries impulses from receptors to the central nervous system and has a cell body positioned alongside the spinal cord.
Relay neurone: Located inside the spinal cord or brain and connects the sensory neurone to the motor neurone.
Motor neurone: Carries impulses from the central nervous system to an effector, such as a muscle or gland.

Label the diagram

Some boxes have lost their names. Pick the right name for each number.

The diagram again, with 3 boxes numbered instead of named. A flowchart running from top to bottom. The first box says the receptor detects a stimulus and points to the second box, where the sensory neurone carries the impulse to the central nervous system. This points to a third box describing the synapse: neurotransmitter released, diffuses across the gap, stimulates the next neurone. This points to a fourth box where the relay neurone inside the spinal cord links sensory and motor neurones. This points to a fifth box where the motor neurone carries the impulse to an effector, and finally to a sixth box where the effector, such as a muscle, contracts.

1Box 1
2Box 2
3Box 3

0 of 3 labelled

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Study notes

The idea

What earns the marks

Common mistakes and how to put them right

Exam tips

Try the lesson

Have a go first

Listen

See it

Put it in order

Key words

Label the diagram

Test your understanding of The human nervous system: Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important.

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