Explain how the structure of a neuron (nerve cell) is adapted for the rapid transmission of electrical impulses over long distances.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The axon is long, allowing impulses to travel over great distances without interruption.
The axon is wrapped in a myelin sheath produced by Schwann cells, which electrically insulates the axon and enables saltatory conduction, greatly increasing the speed of impulse transmission.
Numerous mitochondria are concentrated at the synaptic terminals and along the axon to supply ATP for active transport of ions, which maintains the resting potential and re‑uptake of neurotransmitters.
Dendrites are highly branched, increasing the surface area to receive signals from many other neurons simultaneously.
The axon is wrapped in a myelin sheath produced by Schwann cells, which electrically insulates the axon and enables saltatory conduction, greatly increasing the speed of impulse transmission.
Numerous mitochondria are concentrated at the synaptic terminals and along the axon to supply ATP for active transport of ions, which maintains the resting potential and re‑uptake of neurotransmitters.
Dendrites are highly branched, increasing the surface area to receive signals from many other neurons simultaneously.
Examiner tips
- Use the exact terms – axon, myelin sheath, Schwann cells, saltatory conduction, mitochondria, dendrites.
- Show the link between structure and function – e.g. insulation = faster conduction.
- Include all four points to reach full marks.
- Keep the answer concise and to the point.
Common mistakes
- Confusing Schwann cells with oligodendrocytes (the latter are in CNS).
- Omitting the role of mitochondria in ATP supply.
- Using vague phrases like "long axon" without explaining the functional benefit.
Mark scheme (4 marks)
- The axon is elongated/very long, allowing impulses to be conducted over long distances without interruption.
- The myelin sheath (formed by Schwann cells) electrically insulates the axon, increasing the speed of impulse transmission by saltatory conduction.
- Numerous mitochondria are concentrated at the synaptic terminals / along the axon to supply ATP for active transport of ions (maintaining resting potential / reuptake of neurotransmitters).
- Dendrites are highly branched, increasing the surface area to receive signals from many other neurons simultaneously.
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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