Free nerve ending

A free nerve ending (FNE) or bare nerve ending, is an unspecialized, afferent nerve fiber sending its signal to a sensory neuron. Afferent in this case means bringing information from the body's periphery toward the brain. They function as cutaneous nociceptors and are essentially used by vertebrates to detect pain.

Free nerve ending
Illustration of free nerve endings
Latinterminatio neuralis libera
Anatomical terms of neuroanatomy


Free nerve endings are unencapsulated and have no complex sensory structures. They are the most common type of nerve ending, and are most frequently found in the skin. They mostly resemble the fine roots of a plant. They penetrate the dermis and end in the stratum granulosum. FNEs infiltrate the middle layers of the dermis and surround hair follicles.


Free nerve endings have different rates of adaptation, stimulus modalities, and fiber types.

Rate of adaptation

Different types of FNE can be rapidly adapting, intermediate adapting, or slowly adapting. A delta type II fibers are fast-adapting while A delta type I and C fibers are slowly adapting.[1][2]


Free nerve endings can detect temperature, mechanical stimuli (touch, pressure, stretch) or danger (nociception). Thus, different free nerve endings work as thermoreceptors, cutaneous mechanoreceptors and nociceptors. In other words, they express polymodality.

Fiber types

The majority of Aδ (A delta) fibers (group III) and C (group IV) fibers end as free nerve endings.


  1. Rolf-Detlef Treede, Richard A.Meyer, Srinivasa N.Raja, James N.Campbell. Evidence for two different heat transduction mechanisms in nociceptive primary afferents innervating monkey skin. J Physiol 1995;483:747-758
  2. Churyukanov M, Plaghki L, Legrain V, Mouraux A (2012). "Thermal detection thresholds of Aδ- and C-fibre afferents activated by brief CO2 laser pulses applied onto the human hairy skin". PLoS ONE. 7 (4): e35817. doi:10.1371/journal.pone.0035817. PMC 3338467. PMID 22558230.
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  • Gray's s233
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