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C2.2.4—Variation in impulse speed

Impulse speed increases with axon diameter and myelination because insulation and wider axons reduce resistance to action-potential propagation, linking cellular mechanisms to rapid communication in nervous systems.

Syllabus
First assessment 2025
Objective
C2.2.4
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1A
Typical marks1

Common command terms

  • Describe
  • Determine
  • Calculate
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  • Outline

Recent exam appearances

November 2025Paper1B ["HL"] · TZ13(c)(ii)[ 1 ]C2.2.4—Variation in impulse speed
November 2025Paper1B ["HL"] · TZ13(c)(i)[ 1 ]C2.2.4—Variation in impulse speed
November 2025Paper2 ["HL"] · TZ33(a)[ 2 ]C2.2.4—Variation in impulse speed
November 2025Paper1A ["HL"] · TZ318[ 1 ]C2.2.4—Variation in impulse speed
May 2025Paper1A ["HL"] · TZ317[ 1 ]C2.2.4—Variation in impulse speed
Practice this objective

Coverage 2025–2025 · Updated 15 Jul 2026

Concept essentials

  • Larger axon diameter is associated with faster impulse transmission.
  • Myelin sheath is lipid-rich insulation around axons.
  • Nodes of Ranvier allow ion exchange at gaps in the myelin sheath.
  • Myelination increases conduction speed by supporting saltatory conduction.
ConceptIB Biology HL