GCSE · Biology · AQA · Spec 8461

The human nervous system

Picking up a pencil, a frog snapping up a fly, sweating when you're hot: every one of them runs along the same one-way route.

Follow one message: your body gets too hot

Stage 1 of 7: Stimulus. paused

Stimulus · 1/7drag the impulse →

Your body temperature rises. That rise is the stimulus: a change, and this one is happening inside your body.

Drag the impulse along the route. Each link has to pass the message on before the next one can act.

Where each part belongs

CNS, PNS, or both?

The nervous system has two main sections: the central nervous system (CNS) and the peripheral nervous system (PNS). Tick where each part belongs. Careful: one part belongs in both, and one isn't part of the nervous system at all.

A Central nervous system (CNS)
B Peripheral nervous system (PNS)

The brain
The spinal cord
Relay neurones
Sensory receptors
Neurones (nerve cells)
A sweat gland

What actually counts as a stimulus?

Is a stimulus always something outside you?

Two things happen to you: your body temperature rises, and the lights in the room are dimmed.

Which of these is closest to what you think a stimulus is?

A stimulus is something outside my body, like the lights being dimmed.A stimulus is what my body does about it, like sweating.A stimulus is any change in the environment, inside or outside my body.A stimulus is the part of my body that picks up the change.

How sure are you?

I'm sureI think soI'm guessing

A stimulus is something outside my body, like the lights being dimmed.

This is a common misconception

Half right. The dimmed lights are a stimulus: a change in light intensity, from outside you. But the rise in body temperature happens inside you, and receptors detect that too. So it's a stimulus as well, an internal one.

A stimulus is what my body does about it, like sweating.

This is a common misconception

That's the response, the very end of the chain. The stimulus is at the start: the change itself, such as the rise in temperature. Sweating is what the effector does once the message has got through.

A stimulus is any change in the environment, inside or outside my body.

This matches the evidence

Exactly. The rise in body temperature is an internal stimulus and the change in light intensity is an external one. What makes both of them stimuli is that each is a change that receptors can detect.

A stimulus is the part of my body that picks up the change.

This is a common misconception

That's the receptor, the detector. The stimulus is the change being detected. When the light changes, the change in light intensity is the stimulus, and the light receptors in the retina are what detect it.

A stimulus is a change in the environment, inside or outside the body. Receptors detect it; they are not the stimulus themselves.

Now use the route

Same route, new situations

Pick an item, then choose its job in the pathway.

Still to sort

Stimulus (0)

The change that starts it all

Where the line is: The stimulus is the change itself; the receptor is what detects it.

Receptor (0)

Detects the change

Coordinator (CNS) (0)

Processes the message and coordinates a response

Effector (0)

A muscle or gland that carries out the response

Where the line is: The effector is the muscle or gland; the response is what it does.

Response (0)

What actually happens in the end

8 of 8 still to sort.

You see a pencil and pick it up. A frog sees a fly and catches it. Give every part its job.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

How a change becomes a response: one message, one route

What you need to know

The nervous system lets us sense and respond quickly to changes inside and outside the body.
CNS = the brain and the spinal cord. PNS = every other part of the nervous system.
A stimulus is a change in the environment, inside or outside the body. Receptors detect stimuli.
Sensory neurones carry impulses to the CNS; relay neurones in the CNS pass the message to the brain; motor neurones carry impulses from the CNS to effectors.
An effector is a muscle or a gland, and it carries out the response.

The big picture

Your nervous system lets you sense changes, inside your body and outside it, and respond to them quickly. It has two main sections: the central nervous system (CNS), which is the brain and spinal cord, and the peripheral nervous system (PNS), which is every other part of it. A message travels along one route: from a receptor that detects a change, through the CNS where the response is coordinated, out to an effector, a muscle or a gland, that carries the response out.

Key points

1The brain processes messages and coordinates responses.

2The spinal cord is a dense column of nerve cells that connects the PNS to the brain.

3Neurones (nerve cells) transmit electrical impulses and are found in both the CNS and the PNS.

4A rise in body temperature is an internal stimulus; a change in light intensity is an external one.

5Receptors can be single cells (temperature receptors in the skin) or groups of cells in a sense organ (light receptors in the retina).

6Pathway: stimulus → receptor → sensory neurone → relay neurones (CNS) → motor neurone → effector → response.

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Worked example

Problem

A goalkeeper sees a ball flying towards the goal and catches it. Describe how the nervous system brings about this response.

⚠ Watch out

Swapping neighbours in the chain. The stimulus is the change; the receptor is what detects it. The effector is the muscle or gland; the response is what it does.

🧠

Memory hook

Sense it, sort it, do it. The receptor SENSES the change, the CNS SORTS out what to do, the effector DOES it. And the neurones in between go in, across, out: sensory brings the message IN, relay passes it ACROSS the CNS, motor takes it OUT.

✓

Check yourself

Between the sensory neurone and the motor neurone, which neurones does the message pass through, and in which part of the nervous system are they?

Flashcards

(14)

What does the nervous system let us do?

Sense changes inside and outside the body, and respond to them quickly.

What makes up the central nervous system (CNS)?

The brain and the spinal cord.

What is the peripheral nervous system (PNS)?

Every part of the nervous system outside the CNS.

What does the brain do?

Processes messages and coordinates responses.

What is the spinal cord, and what does it connect?

A dense column of nerve cells that connects the PNS to the brain.

What do neurones do, and where are they found?

They transmit electrical impulses between parts of the body. They are found in both the CNS and the PNS.

What is a stimulus?

A change in the environment, either inside or outside the body.

Give one internal stimulus and one external stimulus.

Internal: a rise in body temperature. External: a change in light intensity.

Receptors can be single cells or groups of cells. Give an example of each.

Single cells: temperature receptors in the skin. Groups of cells in a sense organ: light receptors in the retina of the eye.

What does a sensory neurone do?

Carries electrical impulses from receptors to the CNS.

Where are relay neurones, and what do they do?

In the CNS. They pass the message on to the brain.

What does a motor neurone do?

Carries electrical impulses from the CNS, through the PNS, to an effector.

What is an effector? Name the two kinds.

The part that carries out the response: a muscle or a gland.

How does a sweat gland respond when body temperature rises?

It increases sweating, which helps to cool the body.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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The human nervous system

Follow one message: your body gets too hot

CNS, PNS, or both?

Which way does each neurone carry the message?

Is a stimulus always something outside you?

Same route, new situations

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