A delta fiber
|A delta fiber|
A delta fiber not labeled, but fibers terminate at Rexed lamina I, labeled at upper left.
A delta fibers, or Aδ fibers, are a type of sensory fiber. They respond to stimuli such as cold and pressure, and, as nociceptors, stimulation of them is interpreted as fast/first pain information. Because A delta fibers are thinly myelinated, they send impulses faster than unmyelinated C fibers, but more slowly than other, more thickly myelinated "A" class fibers.
They are thin (2 to 5 μm in diameter), myelinated axons with a moderate conduction velocity, or speed of travel of a nerve signal (2 to 30 m/s). These nerve fibers are associated with acute (sharp) pain and therefore constitute the afferent portion of the reflex arc that results in "pulling away" from noxious stimuli (e.g. retracting your hand away from a hot stove). A certain proportion of Aδ fibers are also associated with sensations of temperature (also known as 'cold receptors' in mammals) and pressure. Slowly conducting, unmyelinated C fibers, by contrast, carry slow, burning pain.
Like other sensory fibers, the Aδ fiber is an extension of a pseudounipolar neuron with its cell body located in a dorsal root ganglion or trigeminal ganglion. Within the spinal cord, afferent nociceptor fibers synapse at or near the spinal cord level where they enter.
- Basbaum et al. 2009. Cellular and Molecular Mechanisms of Pain. Cell 139. DOI 10.1016/j.cell.2009.09.028 - Available at http://ac.els-cdn.com/S0092867409012434/1-s2.0-S0092867409012434-main.pdf?_tid=1ad886f0258c3fb66e249ad7a37df3e2&acdnat=1337524198_340d33507bdc41242daa6a3a72b2cf0a