- C Fibers are small, unmyelinated
nerves with slow conduction velocities that carry
dull, aching burning pain impulses.
- Thinly myelinated A afferent
fibers carry fast, sharp, shooting pain
sensations and are most integral to the
propagation of mechanical pressure stimuli from
muscles, joints, and bone.
- Compared with these fibers, C
afferent fibers have a higher threshold for
mechanical stimuli and a smaller field of
reception.
- Both these classes of nociceptive
fibers ultimately synapse with neurons in the
dorsal horn of the spinal cord.
- The dorsal horn contains several
types of neurons that become hyperexcited by
distinct types of stimuli from primary afferent
nociceptors.
- Class I cells respond to
low-threshold mechanical and thermal
impulses and class III respond only to
stimuli resulting from tissue damage (ie,
they are nociceptive-specific)
- class II neurons have a
wide dynamic range.
- Nociceptive stimuli that
activate these neurons are transmitted to
the brain via the spinothalamic,
spinoreticular, or spinomesencephalic
tracts (STT, SRT, SMT, respectively).
courtesy of Roxane Pain Institute used
with permission http://pain.roxane.com/sitemap.html
|