Lesson 1 of 15
What are the parts of a nervous response?
Cram notes for topic 3.8, The nervous system, in WJEC A level Biology Unit 3.
A detects a and converts its energy into impulses. A carries impulses to the (brain and spinal cord), which coordinates a response. A carries impulses to an , a muscle or gland, which brings about the response.
The diagram below summarises the pathway.
- , , .
- coordinates.
- , , response.
Lesson 2 of 15
What does a transverse section of the spinal cord show?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 2 of 7 WJEC exam series (2017 to 2025), 12 marks in total. This is a revision priority, not a prediction of your exam.
The diagram below shows the main areas of a T.S. of spinal cord.
We recommend revising this because it has appeared regularly in past papers. Asked in 2 of 7 WJEC exam series (2017 to 2025), 12 marks in total. This is a revision priority, not a prediction of your exam.
- in the middle, surrounded by butterfly-shaped (, , ).
- outside, made of ; around the cord.
- carries in; their are in the .
- carries out; their are in the ventral horn.
- The roots join to form a mixed .
Lesson 3 of 15
How does a reflex arc give a rapid, protective response?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 19 marks in total. This is a revision priority, not a prediction of your exam.
A is a rapid, automatic, involuntary response that protects the body. The arc is , , , , .
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 19 marks in total. This is a revision priority, not a prediction of your exam.
- Rapid: only two or three , so few .
- Automatic: the pathway passes through the spinal cord, not the conscious brain.
- The knee-jerk has no , so only one .
Lesson 4 of 15
How does the nerve net of Hydra compare with more complex nervous systems?
Hydra and other have a : short, branched, non- spread through the body wall, with no brain. Impulses spread in all directions and pass slowly, so responses are slow and involve the whole body. Mammals have a , three types of , and one-way impulses, giving fast, precise responses.
Lesson 5 of 15
What is the structure of a motor neurone?
The diagram below shows a .
- with and (rough ER).
- carry impulses towards the ; the carries them away.
- form a lipid , with between them.
- terminals end in on the .
Lesson 6 of 15
How is the resting potential of a neurone maintained?
At rest the inside of the is about −70 mV compared with the outside. The actively transports 3 Na⁺ out for every 2 K⁺ in, using . The membrane is more permeable to K⁺, so K⁺ diffuses out, and large negative ions stay inside.
Lesson 7 of 15
What happens during an action potential?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 6 of 7 WJEC exam series (2017 to 2025), 28 marks in total. This is a revision priority, not a prediction of your exam.
The graph below shows one .
We recommend revising this because it has appeared regularly in past papers. Asked in 6 of 7 WJEC exam series (2017 to 2025), 28 marks in total. This is a revision priority, not a prediction of your exam.
- A opens some sodium ion channels. At (about −55 mV), many open.
- : Na⁺ floods into the ; the inside reaches about +40 mV.
- : sodium channels close, potassium channels open and K⁺ diffuses out.
- : K⁺ channels close slowly, so the potential dips to about −80 mV before the is restored.
Lesson 8 of 15
How does the strength of a stimulus affect the impulses?
are : below there is none, and above they are always the same size. A stronger gives a higher of . The keeps separate, limits their and makes impulses travel one way. In the no is possible; in the only a stronger can trigger one.
Lesson 9 of 15
How do you analyse oscilloscope traces?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 6 marks in total. This is a revision priority, not a prediction of your exam.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 6 marks in total. This is a revision priority, not a prediction of your exam.
- Amplitude = peak − , for example 40 − (−70) = 110 mV.
- Time for one = 1 ÷ ; 200 per second gives 0.005 s = 5 ms.
- Speed = distance ÷ time; convert to metres and seconds first.
Lesson 10 of 15
How does an impulse travel along an axon?
At an , Na⁺ that has entered diffuses sideways inside the . These depolarise the next region to , generating a new . The refractory region behind stops the impulse moving backwards.
Lesson 11 of 15
What affects the speed of conduction of an impulse?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 12 marks in total. This is a revision priority, not a prediction of your exam.
The diagram below shows .
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 12 marks in total. This is a revision priority, not a prediction of your exam.
- insulates the , so happens only at the .
- The jumps from node to node, so less membrane is depolarised and conduction is faster.
- Fewer ions cross the membrane, so less is needed to restore the gradients.
- Wider conduct faster, as in the giant of squid.
- Higher temperature, up to about 40 °C, speeds up of ions.
- slows conduction and increases oxygen use.
Lesson 12 of 15
What is the structure and role of a synapse?
A has a with and of , a presynaptic membrane with calcium ion channels, a cleft about 20 nm wide and a postsynaptic membrane with proteins. make impulses one-way, allow , filter weak and link together.
Lesson 13 of 15
What happens during synaptic transmission?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 5 of 7 WJEC exam series (2017 to 2025), 22 marks in total. This is a revision priority, not a prediction of your exam.
The diagram below numbers the steps of synaptic transmission.
We recommend revising this because it has appeared regularly in past papers. Asked in 5 of 7 WJEC exam series (2017 to 2025), 22 marks in total. This is a revision priority, not a prediction of your exam.
- arrives; calcium ion channels open and Ca²⁺ diffuse in.
- fuse with the presynaptic membrane and release by .
- diffuses across the cleft and binds to ; sodium channels open and the membrane depolarises.
- breaks down ; the products are recycled using .
: several impulses in quick at one . : impulses from several at the same time.
Lesson 14 of 15
How do drugs and other chemicals affect synaptic transmission?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 22 marks in total. This is a revision priority, not a prediction of your exam.
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 22 marks in total. This is a revision priority, not a prediction of your exam.
- block sodium ion channels, so no reaches the brain.
- Calcium channel blockers stop being released.
- Nicotine mimics and stimulates the postsynaptic .
- inhibit , so the postsynaptic membrane stays depolarised.
- such as cocaine block of in the brain.
Lesson 15 of 15
How do the ideas in the nervous system fit together?
- Say 'sodium ions', not 'sodium', and say they enter the , not the membrane.
- do not get bigger with a stronger ; they get more frequent.
- Sensory are in the .
- stop being broken down.
Worksheets
Written by BioWelsh in the style of the WJEC A level Biology examination. Not an official WJEC paper.
Check your understanding.
45 questions. Practise in a focused view, with your answers kept while this page is open.
Related learning
- ATP
The and the resynthesis of use .
- Homeostasis & the kidney
, coordinators and work together in , and detect blood .
- Respiration
use to supply for the .
- Membranes & transport
through channel proteins, and underlie impulses and synaptic transmission.
- Neurobiology & behaviour
Option C develops the brain, and behaviour.
Specification & sources
- https://www.wjec.co.uk/media/mxbh1zaf/wjec-gce-biology-spec-from-2015-e-101025.pdf
- https://openstax.org/books/biology-2e/pages/35-1-neurons-and-glial-cells
- https://openstax.org/books/biology-2e/pages/35-2-how-neurons-communicate
- https://openstax.org/books/biology-2e/pages/35-3-the-central-nervous-system
- https://openstax.org/books/biology-2e/pages/35-4-the-peripheral-nervous-system
- https://openstax.org/books/biology-2e/pages/36-1-sensory-processes
- https://openstax.org/books/biology-2e/pages/28-2-phylum-cnidaria
- WJEC GCE A Level Biology Unit 3 mark schemes, Summer 2017 (Q2), 2018 (Q1), 2019 (Q1), 2022 (Q4), 2023 (Q7), 2024 (Q4) and 2025 (Q5), Unit 5 Summer 2023 variant 2 (Q2), with examiner reports: depth and exam wording
- `u3.nervous-system__photo-hydra.jpg` · Marta Boroń · CC BY 2.0 · https://commons.wikimedia.org/wiki/File:Hydra_oligactis_(35814192232).jpg
- `u3.nervous-system__photo-motor-neurone.jpg` · Berkshire Community College Bioscience Image Library · CC0 · https://commons.wikimedia.org/wiki/File:Nervous_Tissue_Spinal_Cord_Motor_Neuron_(41850850342).jpg
- `u3.nervous-system__photo-nervous-system.jpg` · The Emirr · CC BY 3.0 · https://commons.wikimedia.org/wiki/File:TE-Nervous_system_diagram.svg
- `u3.nervous-system__photo-spinal-cord-section.jpg` · OpenStax · CC BY 4.0 · https://commons.wikimedia.org/wiki/File:1313_Spinal_Cord_Cross_Section.jpg
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- https://creativecommons.org/licenses/by/3.0/
- https://creativecommons.org/licenses/by/2.0/
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