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C2.2.1—Neurons

Neurons are specialized cells with dendrites, cell bodies, axons and terminals arranged to receive, conduct and pass on nerve impulses.

Syllabus
First assessment 2025
Objective
C2.2.1
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper3
Typical marks1

Common command terms

  • Label
  • Draw
  • State
  • Distinguish
  • Identify

Recent exam appearances

November 2024Paper3 ["HL"] · TZ07(c)(ii)[ 1 ]C2.2.1—Neurons
November 2024Paper3 ["HL"] · TZ07(c)(i)[ 1 ]C2.2.1—Neurons
May 2017Paper3 ["HL"] · TZ16(b)[ 2 ]C2.2.1—Neurons
May 2015Paper1 ["HL"] · TZ121[ 1 ]C2.2.1—Neurons
November 2014Paper1 ["HL"] · TZ027[ 1 ]C2.2.1—Neurons
Practice this objective

Coverage 2012–2024 · Updated 15 Jul 2026

Neurons Carry Information through Electrical and Chemical Signals

A neuron is a specialized cell of the nervous system that conducts electrical impulses along elongated nerve fibres.

The cell body contains cytoplasm and the nucleus. Multiple shorter dendrites usually conduct impulses toward the cell body, while one long axon conducts impulses away toward other neurons or effector cells.

Identify the nucleus and cytoplasm in the cell body, then distinguish the long single axon from the multiple shorter dendrites. Fibre length and branching vary with neuron function.

A motor neuron's long axon can carry an impulse from the central nervous system to a distant muscle, while its dendrites receive inputs from other neurons.

An axon and dendrites are cellular projections, not separate cells. Neuron shape varies, so use fibre number, length and direction of impulse rather than assuming every drawing has the same layout.

Neurons exam focus

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through experimental design, commonly using Label / Draw / State.

Command terms

Label / Draw / State / Distinguish / Identify

What earns marks

Build the answer around this relationship: Dendrites receive signals and conduct them toward the cell body.

Representative question

Question 1

[Maximum number: 5]

Draw a labelled diagram of a motor neuron.

SL Transfer: Explain Core Neural Signalling

Neurons carry electrical impulses in the nervous system; motor, sensory, and relay neurons differ in axon, dendrite, and cell body arrangement. Sodium-potassium pumps use ATP to move 3 Na+ out and 2 K+ in; ion gradients make the resting axon polarized at about -70 mV. A nerve impulse is a propagated action potential along a nerve fibre; stimulus-triggered sodium influx reverses membrane polarity. Larger axon diameter lowers resistance and increases impulse speed; myelin sheaths and nodes of Ranvier enable faster saltatory conduction. Synapses connect neurons to neurons, muscles, or glands; chemical synapses transmit one way across a narrow synaptic cleft. Action potentials open voltage-gated Ca2+ channels in presynaptic terminals; Ca2+ causes vesicle fusion and neurotransmitter exocytosis into the cleft. Neurotransmitters diffuse and bind receptors on the postsynaptic membrane; EPSPs depolarize the membrane and make threshold more likely.

Concept essentials

  • Dendrites receive signals and conduct them toward the cell body.
  • Axons conduct nerve impulses away from the cell body toward terminals.
  • Sensory, relay and motor neurons form the main neuron types in reflex arcs.
  • A spinal reflex arc links receptor, sensory neuron, relay neuron, motor neuron and effector.