excerpt
http://www.the-scientist.com/?articles.view/articleNo/35301/title/The-Science-of-Stretch/
Fibroblasts also play a major role in the response to acute injury,
particularly when they transform into myofibroblasts. Before the
availability of surgery and surgical sutures, gaping wounds needed a
powerful mechanism in order to pull shut and heal. Myofibroblasts
serve this function by secreting large amounts of collagen and
expressing a-smooth muscle actin protein, which make the cells
contractile.6 Then, by exerting tension on the collagen matrix, these
cells pull the edges of the wound together. Myofibroblasts normally
die once this job is done and a stable scar has formed. However,
during chronic inflammation, myofibroblasts can drive an excessive
deposition of collagen, and the increased tissue tension can result in
the development of tissue contractures that restrict full range of
motion. This response is also thought to play a role in the
development of some types of tissue fibroses and cancer. Indeed,
fibrotic, or scarred tissues, become stiffer, and cancer cells have
been shown to spread more easily on fibrotic matrices.7
WHEN CONNECTIVE TISSUE STRETCHES
Although much of the work in this area to date has been performed in
cell culture, rather than in whole tissue, some of this basic research
is beginning to inform clinical research and practice, especially in
the area of chronic musculoskeletal pain, including low-back pain. One
of the reasons that low-back pain is so difficult to manage is that
large numbers of patients have no detectable abnormalities of the
spine and associated tissues, and the source of their pain is unknown.
Some groups have begun to investigate the possibility that the pain is
arising from the nonspecialized connective tissues on either side of
the spine.
Indeed, researchers at the University of Heidelberg found in 2008 that
connective tissues contain sensory nerve endings that can transmit
pain when these tissues are stretched in the presence of
inflammation.8 Until then, it had not been clear whether connective
tissue had its own sensory nerve supply capable of generating
sensations. Subsequently, ultrasound studies in my laboratory
demonstrated that the connective tissues that surround the muscles of
the back are, on average, thicker in people with chronic low back
pain.9 Normally, these connective tissues are composed of alternating
layers of tightly woven dense fibers that can bear substantial loads,
and loose areolar tissue, which contains large quantities of water and
allows the adjacent dense layers to glide past one another. In
addition to having thicker connective tissue overall, people with
low-back pain show a decreased gliding motion of dense layers,
suggesting that a fibrotic process could cause the decreased mobility.
The mysterious �acupuncture meridians,� defined as lines or tracks
connecting acupuncture points, also may be related to connective
tissue, as they seem to be preferentially located along
connective-tissue planes between muscles, or between muscle and bone.
We have found that more than 80 percent of acupuncture points in the
arm are located along connective-tissue planes.13 This makes sense,
since loose connective tissue houses blood vessels and nerves,
suggesting that mechanical stimulation of connective tissue generated
by needle manipulation could transmit a mechanical signal to sensory
nerves, as well as intrinsic sensory afferents directly innervating
connective tissue.