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FastestThings

Nerve Conduction

C fiber

Unmyelinated afferents for slow pain and warmth. The shared textbook range is 0.5–2 metres per second, the bottom of this list.

Also known as Group IV, unmyelinated afferent
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Conduction velocity

0.5–2m/s

Sensory afferent class. Textbook range 0.5–2 m/s. The rank uses the top of the range. The row shows the whole range.

OfficialFundamental Neuroscience for Basic and Clinical Applications (opens source in a new tab)

Mechanism

Why it's so fast

C fibers are slow because they have no myelin, so the impulse has to spread along the membrane of a very thin axon.

  1. No jumping

    Without myelin there are no nodes to leap between. Local currents spread along the bare membrane. The shared diameter is 0.2–1.5 µm, and the shared speed is 0.5–2 m/s.

  2. Second pain

    These afferents carry slow, burning pain and warmth. The sharp signal on a faster axon is a different class. The delay people notice is partly this conduction, not a separate clock.

  3. Last even at the top

    Sorting by the top of the range still places 2 m/s below every myelinated class here. Sorting by 0.5 m/s would not change the order.

The fast pain channel is the Aδ fiber.

Provenance

Every measurement

Claimed, measured and official figures side by side, each with its source. The ranked figure is marked.

  1. 0.5–2m/sRanked figure

    Sensory afferent class. Textbook range 0.5–2 m/s. The rank uses the top of the range. The row shows the whole range.

    The Haines table also prints postganglionic autonomic C fibers at 0.5–2 m/s. This row is the sensory Group IV afferent. Guyton and Hall describe C-fiber speeds from about 0.5 m/s up to 2 m/s, which matches the range and is not a tighter figure.

    Official
    Fundamental Neuroscience for Basic and Clinical Applications (opens source in a new tab)

Reference

Specs

Class
C, Group IV
Diameter
0.2–1.5 µm
Myelin
No
Range
0.5–2 m/s

Context

Background

A C fiber has no myelin. The impulse has to spread along the membrane instead of jumping from node to node, and the axon is a fraction of a micrometre to about 1.5 µm across. That is why this class is the slow end of the sensory table.

The three tables print 0.5–2 m/s. The rank uses 2 m/s, the top of the range, which still places C fibers last. The row shows 0.5–2 m/s. A viral sneeze speed is not on this list.

Spot a wrong number?

Every report is read by a person, and corrections are dated on the page.