Free nerve ending
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A free nerve ending (FNE) is an unspecialized, afferent nerve ending. It is unencapsulated and no complex sensory structures exists, such as those found in Meissner's corpuscle or Pacinian corpuscle. They are the most common type of nerve ending, and are most frequently found in the skin. They penetrate the epidermis and end in the stratum granulosum. They are responsible for detecting temperature, mechanical stimuli (such as pressure), touch and pain (nociception). Some FNEs can also detech stretching.
The majority of Aδ (A delta) (group III) and C (group IV) fibers end as free nerve endings. Aδ fibres are thin, myelinated fibers with a large conduction velocity (2 to 30 m/s) and are associated with acute pain. In a real life situation, this is the sharp pain that triggers reflexes which result in the "pulling away" from the stimuli (ie: yanking hand away from hot stove). A certain proportion of Aδ fibers are also associated with sensations of heat and pressure.
C-fibers are unmyeliniated and as a result, have a slower conduction velocity; lower than 2 m/s. These fibers are associated with chronic or dull pain. C-fibers are associated with sensations of cold, as well as mechanical and chemical stimuli. The density for cold receptors in the skin is greater than the density of warm-receptors (by a factor of 5). It is thought that most or all C fibers are nocireceptors (responding only to noxious stimuli).
Different types of FNE can be fast-adapting, intermediate, or slow-adapting. Aδ fibres are fast-adapting, while C fibers are slow-adapting.
See also
External links
- MacIver MB, Tanelian DL. Free nerve ending terminal morphology is fiber type specific for A delta and C fibers innervating rabbit corneal epithelium. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8509835&dopt=Abstract) J Neurophysiol. 1993 May;69(5):1779-83.
- Gray H. Gray's Anatomy (http://education.yahoo.com/reference/gray/subjects/subject?id=233). Online edition. 2000.
- Nociception: Transduction (http://www-medlib.med.utah.edu/pain_center/education/outlines/noci_transduc.html). From the University of Utah.
- Hada R. 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. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2135092&dopt=Abstract) Shikwa Gakuho. 1990 Feb;90(2):161-80.
- Textbook in Medical Physiology And Pathophysiology: Essentials and clinical problems. (http://www.mfi.ku.dk/ppaulev/chapter3/kap.3.htm) Copenhagen Medical Publishers. 1999 - 2000
- Cleland CL, Hayward L, Rymer WZ. Neural mechanisms underlying the clasp-knife reflex in the cat. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2258749&dopt=Abstract) II. Stretch-sensitive muscular-free nerve endings. J Neurophysiol. 1990 Oct;64(4):1319-30.
- Powerpoint presentation (http://www.bms.abdn.ac.uk/undergraduate/ppt/BI20B2%20FBR%20Lecture%202.ppt) from the University of Aberdeen.
- Somatosensory System (http://faculty.ncwc.edu/ddaley/B232%20Somatosensory%20sys.htm) from Dr Daley of North Carolina Wesleyan College.
- Nerve Terminations (http://cats.med.uvm.edu/cats_teachingmod/neurobiology/histology_lab/nerve_terminations/history.html) - CATS (http://cats.med.uvm.edu/) program of the University of Vermont College of Medicine.Template:Anatomy-stub