Free nerve ending

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Free nerve ending
Latin terminatio neuralis libera
Code TH H3.11.06.0.00002
Illustration of free nerve endings

A free nerve ending (FNE) is an unspecialized, afferent nerve ending, meaning it brings information from the body's periphery toward the brain. They function as cutaneous receptors and are essentially used by vertebrates to detect pain.

Structure

Free nerve endings are unencapsulated and have no complex sensory structures, such as those found in Meissner's or Pacinian corpuscles. 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 epidermis and end in the stratum granulosum. FNE infiltrate the middle layers of the epidermis and surround hair follicles.

Types

Free nerve ending have different rate of adaptation, stimulus modalities and fiber types.

Rate of adaption

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

Modality

Free nerve endings can detect temperature, mechanical stimuli (touch, pressure, stretch) or pain (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.

References

  1. ^ 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. 

External links

  • MacIver M, Tanelian D (1993). "Free nerve ending terminal morphology is fiber-type-specific for A delta and C fibers innervating rabbit corneal epithelium". J Neurophysiol 69 (5): 1779–83. PMID 8509835. 
  • Hada R (1990). "[Difference in responses of free nerve endings and Ruffini-type endings innervating the cat mandibular periosteum to square wave pressure stimuli, ramp mechanical stimuli and triangular vibrations]". Shikwa Gakuho 90 (2): 161–80. PMID 2135092. 
  • Cleland C, Hayward L, Rymer W (1990). "Neural mechanisms underlying the clasp-knife reflex in the cat. II. Stretch-sensitive muscular-free nerve endings". J Neurophysiol 64 (4): 1319–30. PMID 2258749. 
  • Somatosensory System from Dr. Daley of North Carolina Wesleyan College.







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