What you need to know
- 8.10The mammalian nervous system has a central and a peripheral part.
- 8.13Coordination uses both nervous and hormonal control.
Named brain regions are 8B 3. The peripheral split is the next lesson. Hormone mechanisms such as peptide versus steroid are Topic 7 and are not repeated as required detail here.
By the end, you should be able to…
- Define the central nervous systemThe brain and spinal cord. as brain plus spinal cord.
- Compare speed, route and duration of nervous and hormonal signals.
- Give one response that uses both.
Build your understanding
Central means brain and cord
The central nervous systemThe brain and spinal cord. is the brain and the spinal cord. It receives sensory input, integrates it, and sends motor output. The peripheral nervous systemAll the nerves outside the brain and spinal cord. is everything else: the nerves that connect receptors and effectors to that centre. 8.10 is this division. It is not a list of lobe names yet.
Grey and white matter, and the withdrawal reflex, are the cord in action. The brain adds voluntary movement, balance, homeostatic centres and hormone release. Those jobs are named by region in 8B 3. Here, know which organs count as central.
Nerves are fast and local
A nervous signal is an impulse in a named pathway. It arrives in milliseconds and stops when the transmitter is broken down. The effector is the muscle or gland at the end of that pathway. A bright light constricts one pupil through a nerve pathway. It does not wait for a hormone to travel round the blood.
A hormone is a chemical released into the blood. It reaches every tissue, but only cells with the right receptor respond. The start is slower to organise and the effect often lasts longer, because the hormone must be broken down or excreted. adrenalineA hormone from the adrenal glands that prepares the body for action, for example by raising heart rate. in a sudden fright is the usual comparison: the hormone supports a response that nerves also start. You can describe that pattern without a full endocrine map.
One behaviour, two systems
Exercise needs both. Nerves withdraw a foot from a stone immediately and drive breathing muscles. Hormones and the longer nervous adjustments keep heart rateThe number of heartbeats per minute. and fuel supply up. If you write only one system, the answer is incomplete for 8.13.
Do not say hormones are always slower in every first step. The useful contrast is route and duration: impulses in neurones versus chemicals in the blood.
NOT: central does not mean the brain alone, and autonomic is not the same as hormonal.
- Central = brain and spinal cord
- Peripheral nerves connect receptors and effectors
- Nervous signals are fast and local
- Hormones travel in the blood
Two traps this diagram blocks
- Do not define the central nervous system as the brain only.
- Do not say a hormone is always the faster route.
From the diagram alone
Question
Compare the route and the duration of a nervous signal with those of a hormone. [3]
Show a model answer
A nervous impulse travels along a neurone to one effector and stops when the transmitter is removed, so it is local and brief. A hormone travels in the blood and often acts for longer, but only on cells with the right receptor.
| Feature | Nervous | Hormonal |
|---|---|---|
| Message | Impulse, then a transmitter at a synapse | Hormone in the blood |
| Route | Specific neurones | Whole circulation, specific receptors |
| Speed and length | Fast, usually short-lived | Slower to arrive, often longer-lasting |
Make your reasoning visible
Name the organs
Central: brain and spinal cord. If you only write “the brain”, the cord is missing.
Route, then speed
A comparison needs the blood versus the neurone, not only the word fast.
Avoid this misconception
The claim: The peripheral nerves are part of the central nervous systemThe brain and spinal cord. because they are connected to it.
The correction: Connected does not mean central. Central is brain and spinal cord only. The nerves are peripheral.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
What structures make up the central nervous system?
Show suggested answer
The brain and the spinal cord.
Practice question
Retrieval and explanation · suggested answer
Give two differences between nervous and hormonal coordination.
Show suggested answer
Nervous messages travel along neurones and are fast and short-lived. Hormones travel in the blood, reach many organs, and often act for longer. Any two paired differences.
Practice question
Retrieval and explanation · suggested answer
Why can both systems be involved in a sudden fright?
Show suggested answer
Nerves give an immediate motor response. A hormone such as adrenaline, released into the blood, prolongs and widens the response. The nerve path is still specific.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
A signal reaches only the iris of the left eye within a fraction of a second and then stops. A second signal still affects liver and muscle several minutes later. Which system fits each, and what would you need to see before you called the second signal a hormone rather than a long train of impulses?
Show a hint
Specific and brief versus widespread and sustained.
Explore the reasoning
The iris response fits a nerve pathway: fast, local, and it stops. The later widespread effect fits a hormone in the blood. You would want evidence that a chemical travelled in the blood and that only cells with receptors responded, not just that some neurones kept firing. The question does not name the chemical.
Recall this lesson
Lesson recall questions
Question 1 of 5: Explain, in causal order, why damage confined to a spinal nerve can remove sensation from one region without destroying the brain.
CNS and PNS
Practice question
Retrieval and explanation · suggested answer
Explain, in causal order, why damage confined to a spinal nerve can remove sensation from one region without destroying the brain.
Lesson: 8B 1: The Central Nervous System
Build the sequence from memory first. Then reveal the model order.
Tap the steps in the order you recall. Tap a placed step to send it back.
- 01Next step
- 02Waiting
- 03Waiting
Tap to place
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
MRI is one way the living brain is pictured
8B · The Central Nervous SystemNIBIB describes MRI as using magnets and radio waves to picture soft tissues, including the brain and spinal cord, without ionising radiation. It also names fMRI as a…Specification 8.10Read & use the scienceClose article
Why this matters
NIBIB describes MRI as using magnets and radio waves to picture soft tissues, including the brain and spinal cord, without ionising radiation. It also names fMRI as a way to watch brain activation during a task. That is context for why the central nervous system can be studied in a living person. The scan names are 8B 3. This page only needs the organs that count as central. 8.10 and 8.13: brain plus cord, and nervous versus hormonal coordination.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.10 Central and peripheral nervous systems.
Use the science
Why is an MRI picture not itself the definition of the central nervous system?
Explore a possible response
The definition is anatomical: brain and spinal cord. A scan is a way to look at those organs. Peripheral nerves are still outside the definition even if a picture shows one of them.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering
The hypothalamus links two kinds of control
8B · The Central Nervous SystemAn Endotext review describes the hypothalamus as a small brain region that connects neural information with pituitary hormone control and wider homeostatic responses. That makes it a useful…Specification 8.13Read & use the scienceClose article
Why this matters
An Endotext review describes the hypothalamus as a small brain region that connects neural information with pituitary hormone control and wider homeostatic responses. That makes it a useful real example of 8.13: nervous signalling can be rapid and targeted while hormones travel through blood and often act over longer times. The two systems interact rather than operating as rival control rooms. Locating the hypothalamus on a brain diagram is only the start; a researcher must ask what signal arrives, which cells release a hormone and what target responds. A scan of its position would not by itself show all those steps.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.13 Nervous and hormonal coordination in animals.
Use the science
Why can a neural input to the hypothalamus produce a response in an organ that is not directly connected to that neurone?
Explore a possible response
The hypothalamus can alter hormone release through the pituitary. The hormone then travels in blood to a distant target with the appropriate receptor.
Explore the source
- Functional anatomy of the hypothalamus and pituitaryEndotext, NCBI Bookshelf