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C2.2.14 (HL)—Summation

Summation combines excitatory and inhibitory postsynaptic effects, determining whether the postsynaptic neuron reaches threshold and fires, linking cellular mechanisms to rapid communication in nervous systems.

Syllabus
First assessment 2025
Objective
C2.2.14
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2018
Most common paperPaper3
Typical marks2

Common command terms

  • Explain

Recent exam appearances

May 2018Paper3 ["HL"] · TZ27(c)[ 2 ]C2.2.14 (HL)—Summation
Practice this objective

Coverage 2018–2018 · Updated 15 Jul 2026

Concept essentials

  • Summation combines postsynaptic effects from multiple presynaptic neurons.
  • Excitatory inputs increase the chance of reaching threshold.
  • Inhibitory inputs can cancel or reduce excitatory effects.
  • Action potential generation depends on the net postsynaptic effect.
ConceptIB Biology HL